Implications
for Long-Term Ecos
July, 2005
Robert W. Gray
R.W. Gray Consulting, Ltd.
Bruce A. Blackwell
B.A. Blackwell & Associates Ltd.
1.0
Executive
Summary
The events of the
2003 fire season demonstrate some of the social, economic, and environmental
problems associated with long-term fire exclusion on fire-adapted ecos
The Board’s objectives in this report are to:
1. Provide an
environmental context for fuel dynamics (i.e., the historic range of
variability for fuel characteristics by ecos
2. Describe a range of natural resource management practices that are contributing to fuel characteristic departure from the historic condition.
3. Provide recommendations to natural resource managers that focus on amending potentially deleterious fuel-generating practices.
All terrestrial ecosystems have evolved over time with certain patterns of disturbance, i.e., frequency, intensity, extent, etc. When the primary disturbance agent is fire this pattern is referred to as the Historic Natural Fire Regime. Fuel characteristics, loading by size, depth, continuity, moisture dynamics, chemical content, greatly influence fire behaviour, fire effects, and subsequently, ecosystem structure, function, and composition. Within each HNFR, fuel characteristics fall within a predictable pattern referred to as the Historic Range of Variability. The central tenet of the HRV concept is the fact that the historic range of conditions, be they structures or processes, provide a scientifically proven baseline from which managers can predict complex ecological reactions to certain activities. For example, wildfire effects falling within the historic range of variability for a select fire regime can be predicted provided there is enough empirical evidence for that particular fire regime and the effects would be considered to be beneficial to the ecosystem as a whole. Fire effects falling outside the historic range would be much more difficult to predict and would likely result in deleterious impacts to ecosystems affected. A great many of the wildfires occurring in the western US and southern BC in recent years produced fire effects well outside the historic range for those fire regimes. Potentially long-term impacts include highly altered soil texture, soil nutrient status, soil microbial diversity, and plant community diversity.
Traditionally, fuel management in BC has had a singular focus on forest fuels generated from industrial activities (B.C. Reg. 38/2005) – our assessment process in fact focuses solely on these activities. However, this has not considered fuel hazards associated with other forest use, forest insect and disease outbreaks, and fire exclusion. Also, the potential long-term environmental consequences of fire, specifically attributed to unnatural burn severity, are not principle to the assessment process. Unnatural burn severity can result from a change in fuel characteristics and the type of wildfire (crown versus surface) that the fuels will support.
The focus of the Firestorm 2003 Provincial Overview (Filmon 2003) was on management of fire risk within the Wildland-Urban Interface. Limited science on fuel hazard identification and mitigation, and application of standards for interface fuel treatments over complex and diverse landscapes are significant challenges for government. Intensive forestry within defined interface areas may be contrary to the goal of fire-risk reduction. New zonation and/or land use designation may be required within moderate and high-risk interface communities to address this issue.
Multiple benefits
accrue from the reduction of wildfire hazard in moderate- and high-risk forests
of BC including improved suppression capability, ecosystem function, forest
health, and protection of biodiversity. Prescribed fire has been identified by many
stakeholders in the province as a beneficial tool for resolving fuels and
wildfire threat (Filmon 2003). However, several issues have limited the
widespread application of the practice of prescribed fire including the failure
of prescribed burns to meet stated objectives and the need to perform repeated
burns in many cases before fuel loading is at a low hazardous level. Fire prone
ecosystems that could benefit from the scientific application of prescribed
fire run the range of fire regimes; from non-lethal, low severity understory
burning to lethal, high severity stand replacement burning. In order for the
province to rapidly build capacity there is a need to investigate and adapt all
appropriate fire behaviour and fire effects prediction decision aids, including
those developed in the
From a biodiversity perspective, static management (preservation) in reserve zones (e.g. riparian, ungulate winter range, old growth management areas, environmentally sensitive areas, etc.) that does not address fuel hazards may jeopardize the long-term sustainability of these ecosystems. To protect these ecosystems it is important to: 1) accommodate fire-related and other ecological processes that maintain aquatic habitats and biodiversity, and not simply control fires and fuels; 2) prioritize fuel treatments according to risk, opportunities for fire control, and protection of biodiversity; and, 3) develop consistent standards for disturbance management actions that are supported by all agencies
This report provides
an overview of some, but not all of the complex problems that government
currently faces in addressing the fuels, forest health and associated wildfire
risk problem in
1.1.1 Synopsis of Key Recommendations
Recommendation 1. Develop a standardized system for the assessment and inventory of forest fuels in areas of moderate and high wildfire risk. The assessment of forest fuel hazards should be broadened beyond the scope of industrial activities to include fuels associated with other human activities (e.g. development), large-scale disturbance by forest insect and diseases, and fire exclusion.
Recommendation 2. Develop fuel management targets for all forest ecosystems where there is moderate to high wildfire risk. These targets should be used to guide appropriate fuelbed characteristics and fire management response and should be consistent with ecosystem process and function.
Recommendation 3. In forest ecosystems where there is a moderate to high wildfire risk, research should be focused on biomass accumulation and decomposition rates to determine the persistence of a fuel hazard.
Recommendation 4: Fuel reduction activities need to be regulated by strong environmental standards that target acceptable fire behavior and burn severity.
Recommendation 5: The government should regulate the treatment of fuel hazards within the Wildland Urban Interface.
Recommendation 6: Incentives are required to encourage fuel mitigation activities in areas of moderate and high wildfire risk. Incentives may include provisions for larger treatment units to increase economies of scale, improving opportunities for utilization of small diameter biomass, and adjustments to the stumpage appraisal system.
Recommendation 7: More clearly defined standards for burn plan content are required. Content should include a clear presentation of the fire environment and fire behavior to meet social, economic and environmental objectives (appropriate fire effects). The achievement of objectives should be monitored and subject to audit.
Recommendation 8: Expand the prescribed fire program utilizing both public and private resources. : Support improvement and development of tools to improve prescribed fire planning and prediction.
Recommendation 9: The province should coordinate and develop a strategic fire management plan considering the patterns of harvest and values at risk within the current mountain pine beetle outbreak. This approach should be refined and adapted to the area of projected outbreak to 2020.
Recommendation 10: Active fuel management should be considered within static reserves located in moderate to high wildfire risk ecosystems. Activities should be linked to scientifically credible measures that ensure maintenance of ecosystem structure, composition, function and process. Strong rationale for treatment, treatment guidelines and standards, and long-term monitoring of ecological effects and treatment effectiveness are required.
Acknowledgements
The authors would
like to thank Brad Hawkes, John Parminter, Cliff White, Steve Arno, Richy
Harrod,
Table of Contents
1.1.1 Synopsis
of Key Recommendations
3.0 Forest
fuel and fire management impacts
3.1 Unnatural build-up of forest fuels
3.2 Departure from Historic Range of Variability
3.3 Potential environmental consequences
3.3.1 Ecosystem
health effects
3.4 Fire in the Wildland Urban Interface (WUI)
5.0 Policy
and practices issues
5.1.1 Fuel
assessment in the Southern Interior Forest Region
Area of juvenile spacing fuels
Area of natural disturbance-related fuels
Southern Interior fuel assessment conclusions
5.3 Forest management activities and their relationship to fuels
5.4 Fuel reduction and forest management in interface areas
5.6 Forest health and its relationship to fuels
5.7 Biodiversity management and its relationship to fuels
5.7.2 Parks
and Protected Areas
Appendix 1: Historic Natural Fire Regimes
Appendix 2: Fire Regime Class for the Southern Interior
of B.C.
Appendix 3: Extent of Insect Activity in the Southern
Interior, 1983-2003
List of Tables
Table 2. Condition Class descriptions (from Hardy et
al. 2001;Hann and Bunnell 2001)
Table 3. The temperature at which important soil
components are volatilized (Agee 1993).
List of Figures
Figure 8. The
three fuel layers that influence fire behaviour and fire effects.
Figure 9. A
wildfire involving all three fuel layers: ground, surface, and aerial (R. Gray
photo).
Figure 12. Summary of total area spaced on Crown land
from 1983/84 to 2001/02.
Figure 23. Surface fuel size class distribution pre- and
post-thin in a commercial thinning unit.
Figure 30. Stream channel damage after the Okanagan
Mountain Park Fire. (Photo courtesy Tim Smith).
2.0 Introduction
During summers like 2003 in
Fire itself is not the real
culprit; most of our terrestrial ecos
Wildfires are the product
of a fairly simple chemical reaction involving oxygen, fuel, and an external
heat source. Once a wildfire starts, weather, topography, and fuels shape its
behaviour on the landscape. While weather and topography are important
contributors to fire behaviour they are beyond our control. The fuel component
of this chemical reaction is the only variable that we, as humans, can
influence. This special report investigates the role that forest fuels play in
fire behaviour and fire impacts in terms of the effect of fire on the long-term
health of ecosystems. Other issues, such as the economic and social costs
associated with increasing fuel load (e.g. prolonged wildfire suppression,
higher costs due extensive mop-up, the need for additional resources, and more
hazardous working conditions for suppression crews, etc.), are not addressed in
this report[1]. The
report pays particular attention to the southern interior of the province; the
area most affected by our fuel and fire management practices, and where the
consequences of those practices are most profound.
3.0
Forest fuel and fire management impacts
3.1 Unnatural build-up of forest fuels
All terrestrial ecos
Accumulation and
decomposition rates are dynamic and vary by ecos
Table 1.
Published decay and accumulation rates for biomass within three western Montana
Habitat Types (data from Harvey et al. 1981).
|
Habitat Type |
Decay rate (m³/ha/yr) |
Accumulation rate (m³/ha/yr) |
|
Douglas-fir/ninebark |
2.1 |
2.8 |
|
Subalpine
fir/queen’s cup-beadlily |
1.9 |
4.4 |
|
Western
hemlock/queen’s cup-beadlily |
3.7 |
4.0 |
Figure 1. Average
annual disparity between fuel accumulation and decomposition rates for a dry
ponderosa pine site (Sackett et al. 1996). Similar ecos
The carbon stored in ecosystems contains energy stored in its molecular
bonds, and energy is released in the form of heat (Cottrell 1989, Pyne 1984).
The higher the quantity of carbon stored on a site the more potential energy
there is to be released. This stored carbon, in the form of litter and duff,
branches, logs and stumps, shrubs, herbs and grasses, and tree crowns, is
potential fuel for a fire.
Our dry interior forests and grasslands historically experienced fires
frequently, resulting in low between-fire fuel accumulations. Historic fires
consumed fuels, releasing important nutrients, without causing extremes in
energy release. Ecosystem productivity and sustainability was actually enhanced
and protected by frequent fire (Baird et al. 1999). In the absence of
fire, fuels have accumulated well beyond the historic levels that these
ecosystems evolved under (Filmon 2003, Gray et al. 2004). Individual
ecosystems (organisms, processes, structures) are adapted to certain critical
threshold levels of energy release over time. Too much energy release occurring
too frequently can result in significant impacts on biological sustainability
and productivity (Agee 1993). Under current fuel conditions, critical
thresholds of energy release can be exceeded during a fire and cause severe
impacts on long-term ecosystem health.
3.2
Departure from Historic Range of Variability
For resource managers, it
is important to know the range of critical ecological processes and conditions
that have characterized particular ecos
The HRV concept is most
valuable when used as a reference against which to compare current conditions
or trends. Where current ecosystem properties or trajectories are not very
different from what would be expected under the historical disturbance regime,
the system is probably functioning normally and human intervention is not
required. However, if current ecological conditions are dramatically different
from historical patterns and trends, then careful assessment of the changes is
warranted, and restoration of some or all of the historical ecosystem
components and processes should be considered (Romme et al. 2003). This
includes the restoration of appropriate ecosystem level fuel characteristics.
Different fire regimes are characterized by different average fire
behaviour. Fire severity is the fire behaviour output of greatest interest; it
is the immediate measure of fire effects and fire lethality. The frequency of
fire, and the between fire fuel accumulation rate, dictates fire severity and
ecos
Figure 2. Example of an infrequent, but high-severity fire
regime. While fire severity was very high on this incident its relatively
infrequent occurrence enables the ecos
In 2003 a fire science research team developed models describing the
Historic Natural Fire Regimes (HNFR) for the southern interior of B.C. plus the
extent of fire regime departure from historic conditions (Blackwell et al.
2003). The HNFR model describes eight fire regimes (see Appendix 1)
(Heinselmann 1981, Agee 1993, Morgan et al. 1996, Brown 2000, Morgan et al. 2001, Schmidt et al. 2002) in a 10 million hectare area bounded by the U.S. border
to the south, Coast Mountain Range to the west, Alberta border to the east, and
the city of 100 Mile House to the north.
The HNFR disturbance classification is distinctly different from the
Natural Disturbance Type (NDT) classification (Ministry of Forests and Ministry
of Environment, Lands, and Parks. 1995) currently being applied to forest
management planning in B.C. The NDT framework is based solely on disturbance
return intervals, which are derived from biogeoclimatic subzones and variants,
and reflect regional climate. When considering fire as a disturbance agent the
NDT classification is limited and does not adequately reflect the effects of topography
(slope and aspect) and variations in fire behaviour which influence fire
severity. This system assumes a static temporal condition existed between
historic conditions and current conditions. Dry forest types are classified as
NDT4; however, in their current condition the fire regime has departed to a
condition closer resembling a very infrequent but catastrophic fire regime
(i.e. stand replacement). The HNFR applied in the 2003 study attempted to
improve our understanding of fire disturbance at the landscape scale and should
be viewed as a higher resolution refinement of the existing NDT system.
The Historic
Regional fire regimes are defined by several parameters including
dominant vegetation (fuel), local climate (weather), landscape characteristics
(topography), and anthropogenic ignition patterns (Wright and Bailey 1982, Agee
1993, Agee 1998, Brown 2000). Landscape characteristics, as reflected by slope
and aspect, greatly influence fire behaviour, particularly in the mountainous
areas of western
The fire regime departure model, named the Fire Regime Condition Class
(FRCC) (Appendix 2), uses a numeric rating to describe the approximate number
of missed fire intervals plus the potential environmental impacts associated
with this condition. The effect of HNFR on forest and range ecosystems produces
a variable, but predictable, range of species and vegetation structures (Brown
2000) including fuelbed characteristics. Shifts in species composition and
vegetation structure have accompanied the interruption of the HNFR across many
parts of the west (Gray et al. 2002, Gray et al.
2004). As a result there has been a significant departure from the species and
structural elements adapted to the HNFR. Were fire to return to these
ecosystems in their departed state, extensive environmental damage could occur.
Not all ecosystems are departed from their historic state, however, and many
fall within a range of departure.
The condition class concept (Hann and Bunnell 2001, Hardy et al.
2001, Schmidt et al. 2002) was developed as a tool for assessing an ecos
Table 2.
Condition Class descriptions (from Hardy et al. 2001;Hann and Bunnell
2001)
|
Condition Class |
Departure from HRV |
Attributes |
Example management
options |
|
Class 1 |
Low |
·
Fire regimes are
within or near a historical range ·
The risk of losing key
ecosystem components is low ·
Fire frequencies have
departed from historical frequencies by no more than one return interval ·
Vegetation attributes
(species composition and structure) are intact and functioning within an
historical range ·
Disturbance agents, native
species habitats, and hydrologic functions are within the historical range
of variability ·
Smoke production
potential is low in volume |
Where appropriate, these areas can be
maintained within the historical fire regime by treatments such as management
ignited prescribed fire or prescribed natural fire |
|
Class 2 |
Moderate |
·
Fire regimes have been
moderately altered from their historical range ·
The risk of losing key
ecosystem components has increased to moderate ·
Fire frequencies have
departed (either increased or decreased) from historical frequencies by more
than one return interval. This results in moderate changes to one or more of
the following: fire size, frequency, intensity, severity, or landscape
patterns ·
Disturbance agents,
native species habitats, and hydrologic functions are outside the historical
range of variability ·
Smoke production
potential has increased moderately in volume and duration |
Where appropriate, these areas may need moderate
levels of restoration treatments, such as management ignited prescribed fire
and hand or mechanical treatments, to be restored to the historical fire
regime |
|
Class 3 |
High |
·
Fire regimes have been
significantly altered from their historical range ·
Fire frequencies have
departed from historical frequencies by multiple return intervals. This
results in dramatic changes to one or more of the following: fire size,
frequency, intensity, severity, or landscape patterns ·
Vegetation attributes have
been significantly altered from their historical range ·
Disturbance agents,
native species habitats, and hydrologic functions are substantially outside
the historical range of variability ·
Smoke production
potential has increased with risks of high volume production of long
duration |
Where appropriate, these areas may need
high levels of restoration treatments, such as hand or mechanical
treatments. These treatments may be necessary before fire is used to restore
the historical fire regime |
3.3 Potential environmental consequences
3.3.1 Ecosystem health effects
The critical thresholds of
energy release, measured at the individual ecosystem component level and in
space in time, dictate how adapted, or resilient, a particular ecosystem is to
fire. Two ecosystem components that allow us to measure fire resilience are
soils and vegetation.
Soils
Soils, and the processes
that occur in the soil, form the foundation for forest sustainability (Neary et
al. 2000). Physical, chemical, and biological processes in the soil are
critical for meeting plant demands for water and nutrients. Root dynamics and
physiology, biogeochemical cycling, microbial, hydrologic and thermal processes
that regulate nutrient storage and flux, and the soil’s ability to hold water
and nutrients, contribute to terrestrial ecosystem sustainability. These
belowground processes, functions, and organisms are necessary to maintain
aboveground ecosystem structure and function (Neary et al. 1999). Fire
can either aid in the long-term productivity of soils or it can severely impact
them. The important points to consider in this discussion relate to the
identification of conditions where soil productivity and recovery are
potentially damaged by fire. These conditions are a function of burn severity (itself
a function of fuel load, fuel bulk density, fuel moisture, and soil moisture),
symbiosis with other disturbances (i.e., heavy rainfall events), and frequency
of fire disturbance.
Soil texture, structure, bulk density, and nutrients are all affected by
fire. Soil texture is rarely changed by fire, although severe heating of
clay-rich soils can result in the aggregation of soil particles. This situation
can occur when soil temperatures exceed 200°C (Agee 1993). Soil structure, the
arrangement of particles in the soil, which also includes the influence of soil
organisms, can be adversely affected by even moderate burn severity (Agee 1993,
Pietikainen and Fritze 1993).
The creation of hydrophobic
soil layers and resultant soil erosion issues are also included in the category
of soil structure. Soil bulk density is an inverse measure of the porosity of
the soil. As bulk density increases, porosity decreases. Porosity is critical
from the perspective of water percolation, infiltration, and holding capacity
(Hungerford et al. 1991). Reduced porosity (increased bulk density) is
often the result of heat damage to insects and other macro-organisms that
tunnel in the soil breaking up bulk density (Agee 1993).
Damage to plant rooting will
also have an impact on porosity. Fire results in the volatilization of
nutrients, which may be lost from the ecos
Table 3. The
temperature at which important soil components are volatilized (Agee 1993).
|
Soil Constituent or Property |
Temperature (°C) |
|
Carbon |
100 |
|
Water |
100 |
|
Hydrophobicity |
175 |
|
Nitrogen |
175 |
|
Organic Phosphorus |
350 |
|
Sulfur |
375 |
|
Clay Aggregates |
500 |
|
Potassium |
550 |
|
Inorganic Phosphorus |
770 |
|
Sodium, Magnesium, Calcium |
>800 |
Maintaining long-term soil productivity
requires the presence of future soil capital, soil organic material, and more
importantly, fire effects characteristic of the natural fire regime. Most fires
that fit this model are likely to enhance soil development and fertility over
the long term by the periodic release of nutrients. However, extremely severe
fires or large, severely burned areas within fires, brought on by either rare
natural events or human activity, are likely to be highly detrimental to forest
soils (Brown et al. 2003).
Based on a cursory
examination of the effects of fire on soils it becomes readily apparent that
the factors affecting burn severity contribute the most to soil productivity
impacts. For example, a very dry fuelbed consisting of deep duff and large logs
would result in extremely high heat output and long residence time with
duration, not heat, being the most critical factor (Neary et al. 2000).
This situation could lead to the following soil property changes: (1) soil
texture change due to fused clay particles; (2) soil structure change, (i.e.,
increased bulk density due to aggregated cla
Figure
3. High
burn severity adjacent to a large log. The fire at this location had long
duration at high temperature, with characteristic signs of high burn severity
including fractured or splintered rocks, white ash, and pink-coloured soil (R.
Gray photo).
Vegetation
The role of vegetation in
maintaining ecosystem resilience to fire is measured in individual plant fire
ecology and the physical and physiological relationship of plants to soils.
Plants have many adaptive traits that enable them to survive fire. The location
of dormant buds, seed storage and dispersal mechanism, and plant phenology are
all part of plant fire ecology (Agee 1993, Miller 2000). For any particular
plant to survive and persist, its adaptive traits must be compatible with the
characteristics of the fire and the timing of its occurrence.
Fire return intervals
influence the distribution of life forms and regeneration modes present on a
site (Ryan 2000). Fires can vary in intensity, duration, severity, and
frequency. Fire severity and intensity have a large influence on composition
and structure of the initial post-fire plant community. The severity of fire,
which depends on the amount and type of biomass present and weather conditions
at the time of the fire, exerts a strong influence on plant survivorship and
regeneration (Figure
4). Fire intensity mostly influences the survival of
aboveground vegetation, while burn severity accounts for the downward heat flux
(Brown 2000). The relative resistance of plant species to damage from fire
depends on the degree and duration of soil heating, the depth of perennating
plant parts, heat resistance, and colonization potential (Wright and Bailey
1982, Hungerford et al. 1991, Agee 1993, Miller 2000). Fires of long
residence time that cover large areas with uniform effects are likely to have
the greatest long-term impacts on plant communities.
Figure
4. Postfire
vegetation recovery varies with fire severity. In this concept of severity
rating, the y-axis represents heat pulse above the fire (fire severity), and the
x-axis represents the heat pulse down into the soil (burn severity) (Ryan
2000).
Plant structure, roots,
rhizomes, and stolons, are anchored in the soil and thus help bind the soil substrate.
Certain plant species, such as ceanothus, lupines, and alder species, have
symbiotic relationships with fungi that convert atmospheric nitrogen to a
soil-based form usable by plants. The annual accumulation of dead material
produced by plants and deposited on the forest floor (also referred to as the
litter, fermentation and humus layers) is the ecosystem’s reservoir of future
nutrients. Belowground plant parts serve as habitat for important soil
invertebrates. Following a high severity fire these physical and physiological
traits can be significantly impacted leading to soil integrity impacts. In this
way the health and resilience of the plant community is directly tied to the
health and resilience of the soil base.
From a management
perspective neither of the latter two events can be mitigated but the factors
contributing to burn severity, especially fuelbed characteristics, can be.
The organic matter situated
atop mineral soil is critical to the long-ter
Figure
5.
A 100-year simulation of duff accretion and periodic fire-caused consumption in
a dry interior Douglas-fir forest. The fire regime is characterized by a mean
fire interval of 10 years but is modeled on a range of intervals and burning
conditions. To put this graphic into context, this same ecos
Contemporary management of
the organic horizons of soils fails to recognize and incorporate the dynamics
of accumulation and decomposition as affected by historic fire regimes, the
departure from that condition, and the potentially significant consequences
should a severe fire occur. This is especially apparent with the more frequent
fire regimes of the southern interior. Current soil management standards and
guidelines (Ministry of Environment, Lands, and Parks and Ministry of Forests
1995) suggest that every effort should be made to not disrupt existing forest
floor accumulations despite the fact that these accumulations may be in excess
of historic levels.
The second paradigm to be reviewed has to do with historically and
ecologically appropriate levels of CWD and their implications for long-term
site productivity (Brown et al. 2003). Coarse woody debris pla
Figure 6. Large, downed pine log burning during an early spring prescribed burn (left) and the remains of the log the following morning (right). Large, old pre-settlement pine logs, while coveted by biologists as CWD, can contain large quantities of resin impregnated in the wood. When these logs burn they tend to burn very hot and are typically completely combusted (R. Gray photos).
3.3.2 Forest health effects
The diverse landscape of
Abiotic disturbances, such as windthrow and fire, may also lead to
mortality both directly and indirectly. Windthrown trees of susceptible species
are the preferred host material for Douglas-fir beetle, spruce beetle, and, to
a lesser extent, western balsam bark beetle. Abiotic damage, particularly
drought, has caused extensive damage in mostly dry low-mid elevation stands. In
1999[3]
and 2004[4]
over 10, 000 ha and 11, 300 ha respectively, suffered drought damage mostly in
lower elevation Douglas-fir ponderosa pine ecosystems in the Kamloops and
Okanagan Shuswap Districts.
The temporal and spatial
scale of insect and or disease activity has resulted in significant, and often
overlooked, fuel hazards in the southern interior. In areas of mixed-species
stands (e.g. Figure
7) an insect or disease pest may kill a specific
species, age-class, or diameter class of the stand but not significantly impact
the dominant stand component, as may also be the case with mountain pine beetle
occurring in pure lodgepole pine stands. Over time the dead trees fall and
build up on the forest floor. Once again the scale of fuels and area affected
are key to the level of hazard. In many parts of the southern interior this
gradual stand thinning has been an ongoing process for the last twenty years
with few stands unaffected by at least one pest. The result is a significantly
larger extent of fuel hazard than is currently accepted.
Figure
7.
Mixed stand of Douglas-fir, lodgepole pine, western redcedar, western white
pine, subalpine fir, and western hemlock. The lodgepole and white pine have
been attacked by mountain pine beetle, the white pine is chronically infected
with white pine blister rust, the Douglas-fir is affected by bark beetles and
western spruce budworm. In canopy gaps created by pine mortality Douglas-fir
has germinated but is growing beneath a canopy of Douglas-fir supporting cyclic
infestations of budworm. The cumulative result of this varied insect activity
is a high surface fuel load of large material suspended off the ground, a very
low crown base height due to a substantial ladder fuel layer, and moderate to
high canopy closure and adequate aerial fuels to support crown fire (R. Gray
photo).
Both the stand structure
and surface fuel characteristics in these areas of small-scale outbreaks constitute
a significant forest health and sustainability threat. However, the extent of
the threat in the southern interior is unknown.
The spatial and temporal
scale of the current mountain pine beetle epidemic in B.C. is likely
significantly departed from previous recorded epidemics. The relationship of
the epidemic to fuels and regional fire regimes is also likely well outside the
HRV. Historic natural fire regimes associated with lodgepole pine-dominated
forests range from infrequent in the dry, cold Chilcotin (Applied Ecosystem
Management Ltd. 2002), to very frequent in the warm, dry Cariboo (Iverson et
al. 2002), to spatially and temporally mixed in the Interior Cedar-Hemlock
(ICH) and Montane Spruce (MS) of the east Kootenays (Gray and Daniels [in press]).
Some of these studies suggest that the stand-level proportion of lodgepole pine
has increased over the last century (Iverson et al. 2002); while at the
same time the age-class distribution of lodgepole pine has been skewed (Hawkes et
al. 2003, Taylor and Carroll 2003). The significant input of beetle-caused
surface fuel throughout the range of lodgepole pine in the province in the near
future, coupled with what we now know about lodgepole pine stand dynamics,
indicates a departure in fuel characteristics.
Modeling results from
Hawkes et al. (2003) suggest that the area of susceptible lodgepole pine
at the turn of the century was substantially smaller than the area susceptible
today, and that naturally occurring fires likely had a large impact on the
spatial age-class distribution of lodgepole. This would suggest that,
historically, the regional context of fuels would include a highly
heterogeneous mix of patch sizes, loads, and ages of material. This is
corroborated by a number of historic fire regime studies within the current
area of infestation. A highly variable mix of burned areas of various ages of
recovery would be interspersed with areas of different fuel characteristics.
This significant level of heterogeneity of fire effects is beneficial to
ecosystem sustainability, diversity, and resilience.
Current efforts to salvage
as much lodgepole pine as possible do not incorporate regional-scale fuel
hazard reduction strategies and could, in the future, result in large wildfires
with large areas of uniform fire effects. Recovery of the heterogeneous
landscape characteristics prevalent before the current epidemic would be
further hampered.
3.4 Fire in the Wildland Urban Interface (WUI)
The Wildland-Urban
Interface (WUI) is commonly described as the zone where structures and other
human development meet and intermingle with undeveloped wildland fuels. This
zone poses tremendous risks to life, property, and infrastructure in associated
communities and is one of the most dangerous and complicated situations
firefighters and wildland fire managers face (Society of American Foresters
2004). The WUI is not as recent a management phenomenon for natural resource
managers to deal with in
Subsequent to the wildfires
of 2003 the WUI has grown in political, social, and economic importance (Filmon
2003). A great deal of research has gone into dealing with wildfire threat to
homes and communities within the interface, including: wildfire threat mapping
(Hawkes et al. 1996); appropriate building materials and landscaping design
(
Fortunately, this situation
has improved due to the study of recent wildfires that have impacted fuel
treatment areas, and the development and constant improvement of fire behaviour
and fire effects models (Fire Program Solutions LLC 2001, Reinhardt et al.
2001, Scott and Reinhardt 2001, Finney 2003, Ryan 2005). The combination of
research findings and improved predictive models can be used with great benefit
to the development and auditing of appropriate WUI fuel hazard reduction
treatments.
A number of researchers
have investigated situations where wildfires have impacted stands that had
previously undergone fuel treatments. These retrospective studies have been
beneficial in clarifying some of the spatial, temporal and intensity issues
related to the effectiveness of fuel treatments in mitigating fire behaviour.
Primary results indicate that the intensity of fuel removal from the treatment
area (Weatherspoon and Skinner 1987), the spatial scale of the treatment
(Finney et al. 2003, Ryan 2005), and the time elapsed between the
treatment and the subsequent wildfire (Martinson and Omi 2003), are all
significant issues. Much of these data have been incorporated into existing
fire behaviour and fire effects models, or are being used in the development of
new models in the U.S. such as Fuel Characteristic Classification System
(Sandburg et al. 2001) and LANDFIRE (Ryan 2005).
4.0 Report Objective
All of B.C.’s terrestrial vegetated ecosystems have evolved under the
influence of a historic fire regime. A fire regime is simply the nature of fire
occurring over long periods and the prominent immediate effects of fire that
generally characterize an ecosystem (Brown 2000). While weather plays an
important role in driving the fires that help define fire regimes, it is fuels
that are the cornerstone of the fire regime itself.
Ecosystems have inherent carbon dynamics shaped by topography (slope,
aspect, elevation) and climate. Moist, productive sites accumulate fuels
rapidly but also have equally high decomposition rates; in fact they rely
heavily on biotic decomposition. These moist sites typically retain high
moisture content in their fuels even through the driest months. The fire regime
in moist ecosystems is therefore characterized by infrequent fire occurrence
owing to poor burning conditions (Agee 1993, Lertzman et al. 2002, Gavin
et al. 2003). Dry, less productive ecosystems accumulate lower
quantities of fuels and have low biotic decomposition rates. However, they are
also characterized by very frequent, favourable burning conditions.
Decomposition of fuel accumulations in these dry ecosystems is therefore
heavily reliant on fire.
The primary objective of this report is to investigate the role that forest fuels play in fire behaviour and fire impacts in terms of the effect of fire on the long-term health of ecosystems with particular attention to the southern interior of the province. The report specifically addresses practices and policy issues related to fuel assessment, fuel management and forestry practice that influence fuels and fire behavior. The following section provides a description of the issue and recommends potential solutions.
5.0 Policy and practices issues
5.1 Fuel assessment
Wildland fuels are described according to their location within the
stand. These layers, or strata, include ground fuels, surface fuels, and aerial
fuels (including ladder fuels) (Figure 8).
Figure 8. The three fuel layers that influence fire behaviour
and fire effects.
Ground fuels consist of duff, peat, roots, stumps, and buried logs. Ground
fuels typically burn by smouldering and may burn for many hours, days, or even
weeks, especially if initial moisture contents are high. This long duration
smouldering can often lead to soil damage and tree mortality (Graham et al.
2004).
Surface fuels consist of grasses, shrubs, litter, and woody material
lying on, or in contact with the ground surface. Important surface fuel
characteristics that determine surface fire behaviour include: fuel bulk
density (weight within a given volume), size class distribution, fuel depth,
horizontal continuity, and chemical content (i.e. heat of combustion or heat
content). Surface fuel complexes with high loadings of large material - for
example, slash left after timber harvesting, pre-commercial thinning operations,
or high fuel loads from natural events such as blowdown or insect epidemic -
have long flaming residence times compared to fine fuels such as grasses or
shrubs (Graham et al. 2004).
Crown fuels (also referred to as canopy fuels or aerial fuels) are those
suspended above the ground in trees or vegetation (vines, mosses, lichens,
needles, branches, etc.). These fuels tend to consist mostly of live, and fine
material, less than 0.6 cm in diameter. Crown fuels are the biomass available
for crown fire, which can be propagated from a surface fire via understory
shrubs and trees, or from crown to crown. The shrub/small tree stratum is also
involved in crown fires by increasing surface fire intensity and serving as
“ladder fuels” that provide continuity from surface fuels to canopy fuels,
thereby facilitating crown fires (Figure 9). These essentially bridge the vertical gap between
surface and crown strata. The size of the gap is critical to ignition of crown
fire from a surface fire below.
Aerial fuels separated from surface fuels by large gaps are more
difficult to ignite because of the distance above the surface fire, thus
requiring higher intensity surface fires, surface fires of longer duration that
dry the canopy before ignition, or mass ignition from spotting over a wide
area. Once ignited, high-density canopy fuels (measured as canopy bulk density)
are more likely to result in an active crown fire than low-density canopies
(Graham et al. 2004).
Figure 9. A wildfire involving all three fuel layers: ground,
surface, and aerial (R. Gray photo).
How is a fuel hazard
defined and is the scale of the problem assessed in both time and space? There
is legislation in the province that helps define a fuel hazard. This assessment
combines elements of fuel hazard with values (proximity to homes and
communities, etc.) and risks (history of ignitions, weather patterns, local
climate, etc.) to come up with a sliding scale of fire hazard. Fire or fuel
hazard assessments have been in effect in B.C. in one form or other for as long
as there have been regulations governing forest management. In fact, under the Forest Practices Code a Fire Management
Guidebook (Ministry of Environment, Lands and Parks and Ministry of Forests
1995) was developed that describes the assessment procedure and provides a list
of treatments aimed at reducing hazard. Unfortunately, the guidebook never made
it beyond the draft stage.
Despite having a regulatory
definition and standards for identifying a fuel hazard[5],
very little actual enforcement of the regulations has taken place. Other
jurisdictions, the states of
Another issue with the fuel
hazard appraisal system in the province is the fact that it assesses fuel
hazards – and subsequently wildfire hazards – from a strictly fire suppression
perspective. The potential long-term environmental consequences of a fire,
specifically attributed to unnatural burn severity, are not central to the
assessment process. Unnaturally high concentrations of surface fuels or ground
fuels under significantly departed conditions should be a contributing factor
in hazard appraisal.
The third issue with the fuel
hazard assessment process is its singular focus on fuels generated through
“industrial” activities (B.C. Reg. 38/2005). The Wildfire Act regulations define industrial activity for the sake of
assessing fuel hazards. However, as is pointed out in this report, a
substantial fuel hazard exists due to insects and diseases (i.e., agents
causing tree mortality), and fire exclusion (i.e., fuel accretion). When fuels
are generated outside of the regulatory defined means, the land manager is
alleviated from following the regulations for managing a known accumulation of
fuels because of land-use constraints or economics.
The spatial and temporal
context of fuels can be assessed using direct inventories of fuels – when and
where they were created – or through surrogates such as algorithms and models.
Fuels are not directly inventoried in the province outside of a few small-scale
fuel mapping projects (e.g., Merritt Fire Zone) or even smaller-scale
assessments linked to prescribed burns. Following timber harvesting, timber
waste is assessed as per regulations, which is economically driven, but fuels
are not. Other jurisdictions routinely collect and record fuel strata data pre-
and post-management activity and have it geo-referenced for use in fuel and
fire management planning. This results in a more detailed, and accurate
database on fuelbed characteristics.
Current multi-attribute
resource inventory systems (e.g., Vegetation Resource Inventory) and databases
(e.g., Forest Inventory Planning) in B.C. have not been developed with
protocols for either inventorying or storing spatially explicit fuel
characteristics data. This is unfortunate considering the diverse forest
attributes being inventoried using these systems.
Other fuel assessment
methods have been employed in B.C. in place of field inventories. The province
developed an algorithm linking provincial forest cover information (Hawkes et
al. 1995) to the Canadian Forest Fire Behaviour Prediction System national fuel
types. This system has identified 16 benchmark fuel types based mostly on
vegetation type, not specific fuelbed characteristics (Van Wagner et al.
1992). Each forest cover polygon in the province has been assigned a fuel type
based on the overstory tree species. The system has its greatest utility in
emergency wildfire suppression planning. There are consistent issues, however,
related to the accuracy of this system for more involved fuel and fire
management planning.
A predominant issue is the
accuracy of overstory tree characteristics as an indicator of surface-level
fuel characteristics (Figure
10). There are also issues around the temporal context
of fuel classification.
Figure
10.
There are often discrepancies between the modeled fuel conditions using a
narrow range of potential fuel characteristics and actual fuelbed
characteristics. The picture on the left, representing one of the 16 national
fuel types, is used in mapping B.C.’s fuel types. The photo on the right is the
actual stand and fuelbed characteristics at that location.
The Historic Natural Fire
Regime and Fire Regime Condition Class models can be described as fuel hazard
indicators, but they are not quantified fuel inventory systems. Each HNFR is
characterized by a range of fuelbed characteristics, while the corresponding
FRCC provides a measure of potential environmental consequences due to fire
exclusion (e.g., fuel accumulation). FRCC is therefore useful for spatially identifying
where fuel hazards exist but it does not quantify the corresponding fuel
characteristics responsible for the fuel hazard.
5.1.1 Fuel assessment in the Southern Interior Forest Region
Without either a
comprehensive database of fuels based on regular field inventory, or an
accurate model-derived inventory system, there is little chance of fully
quantifying the fuel hazard situation in southern B.C. In this report we have
chosen to look at disturbance rates over the last 20 years as a coarse-scale
surrogate for fuel accumulations. This
exercise serves to provide an example of several of the parameters to consider
in spatial fuel analysis as well as points out the inherent limitations of the
data available for the assessment. The
reader must keep in mind that this is nothing more than an example analysis.
Quite simply, our
quantitative analysis of fuel accumulation was based on the combined gross area
of harvest minus area of fuel treatment, plus gross area of insect infestation,
to produce a very rough estimate of area of significant fuel accumulation.
Caveats to this approach are many and include: (1) harvest area utilization;
(2) fuel treatment success; and (3) the assumed link between insect
infestations and surface and aerial fuels.
Harvest unit utilization
varies tremendously across the province. In areas of very high utilization
post-harvest fuel load is low, whereas where utilization is very poor (e.g.,
helicopter harvest units) post-harvest fuel load is high. It may be possible to
develop some level of correlation between waste and residue survey data and
fuel load of merchantable-size class fuels; however, to date this has not been
attempted. Also, waste and residue survey data does not include fuel size
classes below merchantable log sizes.
For the sake of this exercise it was assumed that all harvest area
constituted some level of fuel hazard.
Fuel treatments, the
converse of fuel-generating activities, are assumed to meet their objective of
fuel hazard reduction over the 20 year analysis period (fuel treatment
effectiveness is time-dependent). As will be discussed, this is not always the
case. In this coarse-scale analysis of fuels, fuel treatment activities are
assumed to have been successful; therefore, gross fuel treatment area is subtracted
from gross harvest area.
Lastly, there is a link
between insect activity and fuel input rate that varies by a number of factors
including intensity of infestation, success of infestation, snag fall rates,
etc. In this analysis we assumed that the area of infestation equated to an
equal area of fuel hazard. Once again,
this analysis is intended to provide a very coarse-scale estimate of the level
of fuel accumulation contributed by a range of sources, it is not intended to
provide the most accurate assessment of fuel accumulations over the target area
or over the target time period.
Area of timber harvest fuels
Timber harvesting within
the dry forest region of the Province (Southern Interior Forest Region) has
varied significantly between 1980 and 2002, ranging from a low of 59,611 ha in
1981 to a high of 132, 575 ha in 1987. The average annual area harvested within
this same period was 92,342 ha (Figure
11).
Figure
11.
Summary of the area harvested between 1980/81 and 2001/02 in the Southern
Interior Forest Region.
While the area of harvest
within the Southern Interior Forest Region is extensive, the legislation (specifically
Sections 79 and 80 of the
- Within 30 days of completion
of timber harvesting activities, a fire hazard assessment must be
conducted to determine the risk of fire on the area where timber was
harvested.
- Any fire hazards resulting
from a forest practice must be reduced to an acceptable level within 12
months of assessment, or within 12 months of when the fire hazard was
created.
- Fuel management planning is
required under development plans and Silviculture Plans.
In
A review of compliance and
enforcement annual reports (1999-2004) shows that the number of formal
enforcement decisions related to the Fire
Prevention and Suppression Regulation totals 39. Thirty-two of these formal
decisions occurred in 2003/2004. For the years 2001 to 2003 no formal decisions
related to the Fire Prevention and
Suppression Regulations are highlighted in the reports. These statistics
can be interpreted in a number of ways: 1) harvest related fuels are being
treated in a timely and appropriate manner post-harvest; 2) harvest related
fuels are not considered a significant issue and therefore are not a high
priority within the compliance and enforcement mandate, and; 3) there is
limited understanding of the hazard and risk of post harvest fuels within
government and industry.
No provincial statistics or
inventory information are available that can be used to determine post harvest
fuel conditions and resulting fire risk.
Area of juvenile spacing fuels
Spacing is defined as the
cutting of undesirable trees within a young stand to reduce competition among
the residual trees. The cut trees (slash) are usually not removed from the
site.
The practice of spacing in
Southern Interior as a silviculture tool saw limited application, primarily for
research, in the 1960s and 1970s. A global recession and incentives to create
employment during the early 1980s resulted in broader use of spacing as an
acceptable silviculture tool for stocking control. Since that time, the area
treated by spacing has steadily increased; reaching levels in the 1990s that
exceeded 35,000 hectares per year (Figure
12). While there are specific guidelines related to the
management of spacing slash in areas of high fire hazard it is uncertain how
widely and consistently these have been applied (http://www.for.gov.bc.ca/hfp/pubs/pct/index.htm). Recent changes to the Forest
Practices Code and reductions in silviculture funding may result in a
decline in the area spaced, however, this practice has resulted in large areas
of contiguous surface fuel throughout many parts of the province. Within fire prone
ecos
Figure 12. Summary of total area spaced on Crown
land from 1983/84 to 2001/02.
Area of pruning
Pruning is the removal of
branches from the stem of a tree to promote the production of knot-free or
clear wood.
Compared to juvenile spacing, pruning as a
silviculture treatment has been less widely prescribed. Figure 13 shows the area pruned between 1991/92 and 2001/2002
within the Southern Interior Forest Region. Pruning from a fuels perspective
creates surface fuel, which may or may not be considered a hazard depending on
the type, amount, and distribution of the fuel (pruned branches). Typically
pruning is conducted in pole sapling stands where the crowns are low to the
ground surface. If the pruning lift is sufficient to increase the crown base
height this may reduce the ability of fire to move from the ground surface into
the crowns. Alternatively, where the fuel created by pruning increases the surface
fuel continuity, this may facilitate propagation of fire into the tree crowns.
In this circumstance the impact of pruning on fuels and fire risk would be
deemed negative.
Figure 13. Summary of total area pruned in the Southern Interior Forest Region from 1991/92 to 2001/02.
Area of natural disturbance-related fuels
In stark contrast to the
area of harvest-related fuels are the potential separate and aggregated areas
of insect-related fuels (some insects overlap with others resulting in the
duplication of some areas of attack). Over the last twenty years[7]
the areas of infestation by four significant insect pests has grown
significantly (Figure
14) with the mountain pine beetle being the largest by
far. While a proportion of this area has likely been treated to some extent
through harvest it does not remove it from the fuel hazard column and place it
in the fuel treated column unless utilization was very high and the harvest was
followed by prescribed burning, pile burning, and or mechanical treatment .
This exercise reveals two
significant points: (1) the substantial disparity between fuel-generated area
and fuel-treated area; and, (2) the complete lack of accurate fuel accounting
in the province.
Figure
14.
Twenty-year, non-cumulative gross area of bark beetle activity in the Southern
Interior Forest Region. Actual area infested will be smaller due to assignment
of severities to individual polygons.
Area of prescribed fire
Until the late 1980s
prescribed burning was a common forestry practice within the Southern Interior
Forest Region (Figure
15). Within the Southern Interior Forest Region the highest
levels of prescribed burn area in any given year represent approximately 30,000
ha, or approximately10% of the harvest area. Since the early 1990s the area
treated has declined dramatically to lows of <5,000 ha. Environmental
concerns related to smoke management and the risk of escapes prompted a
significant decline in the area burned.
Figure
15.
Summary of the area burned for site preparation – broadcast and spot burning
1980/81 to 2001/02. (Source Ministry of Forests –
Southern Interior fuel assessment conclusions
This exercise has benefit in identifying several readily identifiable sources of fuels (i.e., harvesting, incremental silviculture practices) plus a less commonly accepted source of fuels (i.e., insect activity). The area of harvest activity is significant; whether or not all of this area contains a fuel hazard is debateable. Utilization will have resolved the issue on a proportion of the area, however, an exact amount is unknown. Therefore, it is likely that a proportion of the approximately 1.8 million ha harvested in the Southern Interior in the last 20 years contains a fuel hazard.
Added to this is the area of spacing. There is little room for debate on spaced area; these areas do not see biomass removal as part of the operation and subsequent fuel treatments are non-existent. Gross area of spacing then equates to a gross area of hazard. Pruning is likely less of an issue and more problematic to quantify. There is likely an overlap between spaced areas and pruned areas so adding the two areas together would be erroneous. Pruned material also has higher decomposition rates than spaced material.
Area of fuel hazard reduction is a potentially balancing influence over the area of generated hazard. Unfortunately, there has been very little fuel hazard reduction hectares. In fact, the area of spacing over the last 20 years is roughly equal to the area of fuel hazard treatment. This means that fuel treated area negates spaced area but has no impact on harvested area. A strong caveat to this is of course the immediate and long-term effectiveness of the treatment.
The area of insect activity is also significant from a fuel accumulation perspective. Only insects considered to result in mortality in most cases (bark beetles) versus insects that damage trees (defoliators for example) were used in the analysis. Over the last 20 years there have been several large irruptions in bark beetle populations followed by collapses. Over that same period however there has been a significant area of insect-caused tree death. The connection between this area and actual fuel accumulation is dependent on many factors including host species density in the stand, proportion killed, snag fall rate, etc., and is likely to be very difficult to accurately assess. This exercise was not however intended to put a hard and fast number on fuel hazard area due to insect attack but point out the necessity of including this fuel source in the spatial fuel appraisal formula.
This exercise was known at the outset to likely cause some controversy. The methodology is certainly debateable as are the conclusions. However, the area of human- and natural-caused fuels generated over the last 20 years is likely to be quite high and little mitigation, either through increased utilization or fuel treatments, are actually taking place. To suggest otherwise would be imprudent. The next step is to accurately quantify the area of hazard from all sources and develop the means to reduce it.
5.2 Fuel Mitigation
Fuel treatments are
intended to impact surface fuel characteristics positively by reducing
subsequent fire behaviour and burn severity. The post-fuel treatment stand
should be a wildfire resilient stand – at least until the prescribed
maintenance treatment. Unfortunately, the few hectares being treated by
prescribed fire are quickly being planted back to a future high hazard
situation. The only programs not following this pattern are the few “ecosystem
restoration” programs located in the north and southeast of the province.
Fuel treatment success lies
in the successful reduction of hazardous fuel characteristics (Martinson and
Omi 2003). Many fuel treatments are assumed to have been successful in meeting
the single objective of reducing a fuel hazard. In their examination of the
effectiveness of fuel treatments in mitigating fire behaviour on the 56,000 ha
Hayman Fire in Colorado in 2002, the fire behaviour assessment team (Finney et
al. 2003) only considered whether or not a fuel treatment had taken place
in their analysis, they did not consider whether or not the treatment had
accomplished what it was intended to do.
In cases where prescribed
fire is following behind some form of thinning treatment the ability to reduce
surface and ground fuels to a level approaching the HRV is hampered by the need
to limit burn severity. With close to a century of fuel accumulation, plus the
input of thinning material, the approach should be to incrementally reduce
surface fuels over time with a series of burns, and not succumb to the
temptation to try to reduce all of the accumulated fuel in one burn (Arno and
Allison-Bunnell 2002). This fact was recognized as early as the 1970s by burn
practitioners in
Figure
16.
Surface fuel load trend in a prescribe burned interior Douglas-fir shelterwood
unit (R. Gray photo).
The initial pre-burn fuel
load was only reduced by 10% as a result of the burn. It should be remembered
that this pre-burn load is a combination of fire exclusion caused accumulation
plus thinning-generated fuels. Within one year there is a substantial (50%)
input of fine fuels (needles) from crown scorch. Within less than 10 years any
trees killed by the burn are on the forest floor quadrupling the initial fuel
load. Growing through this surface accumulation will be approximately 1200
trees/ha of planted trees plus an unknown quantity of naturally regenerated
trees.
The only program in the
province that is attempting to resolve the accumulated fuel hazard over the
course of several treatments is the ecos
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Figure
17.
Photo on the left is the spring following an August wildfire while the photo on
the right is of a spring prescribed burn. Almost 8 months after the fire and
the burn severity is still very evident (left) whereas burn severity on the
prescribed burn (right) was very low (R. Gray photos).
5.3
Forest management activities and their relationship to fuels
The actual quantity of
surface fuels left is largely a function of biomass utilization. Some material
is certainly necessary for long-term site productivity and wildlife habitat,
however, the required quantity varies greatly by ecosystem. Once again, too
much material - especially large diameter fuels - can result in significant site
degradation and long-term, impaired site productivity should a wildfire occur.
Clearcut logging leads to a
fairly simplified and homogeneous fuelbed (Figure
18). Typically only two stratum exist: ground fuels and
surface fuels. Low levels of utilization usually result in significant fuelbed
depth and loading. Fuel moisture is maintained at a low level in large openings
where wind and sunlight act to desiccate fuels. The distribution of size
classes is a function of pre-harvest stand conditions and utilization. Openings
with high loading of large materials pose the greatest threats to soil
integrity due to energy release and duration.
Clearcut opening fuel
characteristics do not mimic historical or natural disturbance events outside
of very small, stand-level events in certain ecosystems. Small-scale
disturbances such as windthrow, root-rot infection, and insect infestations,
all produce small-scale inputs of surface fuels, the scale of which depends on
the ecosystem and disturbance intensity. In the southern interior forests of
B.C. small-scale disturbance would not be an uncommon occurrence in the more
productive forest types characterized by less frequent fire. Examples of these
forest types include interior western redcedar-western hemlock forests, or
moist western white pine-dominated forests. These forest types are
characterized by fire-induced gap dynamics of varying scales, with gap, or
patch size, increasing with increased fuel load and interval between fires
(Agee 1998).
From a regional, or
landscape context the scale of clearcut-derived fuels is likely well outside
the HRV. Historically, there would be a juxtaposition of patches of high fuel
load scattered across the landscape. These patches would vary in space and time
as they are attended to by natural fire. Considering the rate of harvest over
the last two decades versus the rate of fuel treatment over the same time
period, it is highly likely that the regional fuel situation is markedly
different in space and time from the historic condition.
Figure
18.
Surface fuel complex remaining after clearcut logging. Two strata of fuels are
present in this situation, ground fuels and surface fuels (R. Gray photo).
Less intense levels of harvest
such as seedtree, shelterwood, single-tree selection, and commercial thinning,
result in a wide range of fuel characteristics and potential consequences.
Seedtree treatments (Figure
19) can produce very similar fuel characteristics to
clearcuts: uniform, deep fuelbeds, high loading, and low fuel moisture content.
Once again, pre-existing stand characteristics and utilization play a large
role in post-harvest fuelbed characteristics. On the positive side, seedtree
units, like clearcut units, have the advantage of fairly inexpensive and, if
done correctly, successful fuel treatment options. It is much easier and less
expensive to carryout prescribed burns or other fuel mitigation treatments on
clearcut or seedtree units versus units with higher residual densities.
With decreasing harvest
intensity comes increasing density of residual stems and the need to consider
the consequences of aerial fuel stratum as well as surface and ground level
fuels. Shelterwood[8] s
Figure
19.
A seedtree unit underburned in a wildfire. The fire exhibited various levels of
severity depending on fuelbed characteristics. In areas of fine fuels, such as
litter and pinegrass, the fire scorched the lower crowns of seedlings but
didn’t kill many trees – even fire-intolerant lodgepole pine. However, when the
fire burned through large logs it exhibited much higher severity killing most
seedlings and saplings within 0.5 m of the fuel (R. Gray photo).
Single-tree selection or
small patch cut s
These systems, where
“thinning from above” is employed in dry forest types do not mimic the effects
of historic disturbance regimes (Martinson and Omi 2003) especially if applied
to large parts of the landscape. There is, however, a historic corollary for
single- or group-overstory trees to be killed in these forest types. These
small patches of dead and downed material would burn under higher severity in
the next fire than adjacent areas and would become suitable substrate for
regenerating trees (Cooper 1960). The historic structure, however, would not
include large expanses of multi-layered forest, including a large proportion of
shade-tolerant and fire-intolerant species, mixed in with close to a century of
accumulated fuels.
Figure
20.
A shelterwood unit underburned in a wildfire. The unit exhibited fairly
uniform, low-severity fire likely due to very low post-harvest fuel load. The
fire selectively thinned the most fire-intolerant species and any sapling
within 0.5 m of a large log (R. Gray photo).
Commercial thinning
activities tend to fit into the category of low-intensity thinning and therefore
should not be producing large quantities of surface fuels. The activity itself
is not intended to be a regeneration cut but an intermediate cut with the
intention of the stand adding increment and leading to another more intensive
cut in the future (Nyland 1996). Utilization and the stand structure
pre-thinning once again play a significant role in determining post-thinning
fuel characteristics. In Figure
22 the interior Douglas-fir stand was commercially
thinned, however, the stand also contained a very high component of
small-diameter, non-merchantable material that was cut and left on-site. In
addition to a significant increase in fuel load (Figure 23), especially in the large diameter size class, fuelbed
depth increased >400% from 9.8 cm to 41.4 cm, as did the porosity of the
fuelbed. The reduced canopy cover will result in a flush of grass adding to the
fine fuel category.
The reduced density of
small diameter trees, which would fit the definition of “ladder fuels”, did not
completely reduce the risk of crown fire owing to the high load of surface
fuels, high canopy bulk density, and relatively low crown base height. The
structure of the fuelbed and the residual stand makes fuel hazard reduction extremely
difficult and expensive.
Figure
21.
Small openings (singletree or small clumps of trees) due to historic selection
harvesting and past insect and disease mortality have led to the creation of
some of the most complex fuel hazards in the province. In the opening (A),
highly shade-tolerant Douglas-fir has enough light to regenerate, there is also
sufficient light to encourage herbaceous growth. Various ages of regenerating
Douglas-fir (B) have enough “side light” to retain live crowns to the ground
enabling easy transition from surface fires to crown fires. Dense thickets (C)
between openings are characterized by heavy branching, including mistletoe
brooms, and high surface fuel accumulations. This structural pattern facilitates
the spread of mistletoe resulting in highly inflammable “brooms” (R. Gray
photo).
Figure
22. Before
and after photos of a commercial thin unit. Merchantable material was removed
however, a great deal of surface fuel was generated from unmerchantable stems.
The residual stand structure (density, canopy closure, diameter) makes
post-thinning prescribed fire – as a fuel reduction treatment – very difficult
(R. Gray photos).
Figure
23.
Surface fuel size class distribution pre- and post-thin in a commercial
thinning unit.
Stand tending activities,
also known as incremental silviculture, are intended to add economic value to a
stand; however, these activities often result in significant quantities of
fuels and also leave little opportunity for fuel treatment due to the residual
stand structure. An example of this is juvenile spacing (Figure 24). Under this type of treatment excess density is
felled and left to decompose.
Several decades after the
1938 Bloedel Fire on Vancouver Island a large proportion of the regenerating
forest was thinned resulting in a short-term but significant fuel hazard.
Aerial suppression resources were based within a two-minute response distance
due to the level of hazard. Therefore, even in moist ecos
The structure of spaced
stands and the surface fuel characteristics leave little opportunity for fuel
abatement. Fires in spaced stands tend to be severe owing to the accumulation
of large-diameter material. From an economic perspective, a significant
investment has been made in juvenile-spaced stands and pruned stands creating
an even greater financial deficit in the event the stand is lost to wildfire.
Figure
24.
Juvenile spacing slash in an interior Douglas-fir stand. So long as the
material sta
Forest management
activities produce variable quantities of fuel, most of which is not
subsequently addressed through some form of post-harvest fuel treatment. In
most cases, new forests are simply planted through the fuel with the
expectation that the forest will survive through to rotation. There are likely
many reasons for a general lack of fuel abatement post-harvest, including: (1)
an aversion to risky treatments such a prescribed fire; (2) the pervasive view
that the fuel decomposes quickly; and, (3) a failure to appreciate fire hazards
and site productivity consequences. Few of these opinions have been documented
outside of the aversion to prescribed burning (Burton 1992). The lack of
available
5.4 Fuel reduction and forest management in interface areas
In this section of the
report the basic principles of fire behaviour management in the WUI are
discussed with particular emphasis on the implications of long-term fuel hazard
management.
When presented with an
identified fuel hazard adjacent to an interface community, there are three
simple questions whose answers should be key to the development or review of an
interface hazard reduction prescription:
- How will the treatment(s)
positively affect fire behaviour and the creation of spotting material?
- How will the treatment(s)
affect local suppression capabilities?
- How long will the positive
benefits of the treatment last (i.e., what is the long-term vegetation
response)?
The primary objective
behind fuel treatments is to have a positive effect on fire behaviour, while
the secondary objective is to create a long-term wildfire resilient stand structure. This means reducing the overall fire
intensity (e.g., flame length, rate of spread and reducing creation of
long-range spotting material) and severity (e.g., crown scorch, active crown
fire) of a potential wildfire by manipulating the three fuel strata. It should
be noted at the outset that these treatments are not intended to stop a
wildfire, only mitigate its behaviour and allow a stand to survive the passage
of a wildfire (Finney et al. 2003, Jain and Graham 2004). Treatments
that will actually stop a wildfire typically involve the full removal of fuels,
which is very difficult and expensive to accomplish and to maintain.
Failure to reduce fire
intensity and severity could result in the loss of the stand, leading to the
future input of fuels (provided the burned stand is not salvaged), the regeneration
of a new stand, and the long-term management of the new stands density so that
it positively influences fire behaviour. This could be a very long-term, and
expensive fuel management problem.
Treatments targeting one or
all of the three fuel strata should have an impact on fuel characteristics, the
stand level fire environment, and, ultimately, fire behaviour. This concept is
best illustrated using a comparison of three treatments applied to the same
fictitious stand structure (Table
4).
Table 4.
Model inputs and outputs for three different fuel treatment scenarios.
The Fuel Management Anal
|
|
No Treatment |
Thin Ladder Fuels/Reduce
Surface Fuels |
Heavy Overstory
Thin/Reduce Surface Fuels |
|
Model Inputs¹ |
|
|
|
|
FBPS Fuel Model |
10 |
8 |
2 |
|
Overstory density (t/ha) |
1500 |
1200 |
200 |
|
Understory (ladder) density (t/ha) |
500 |
0 |
0 |
|
Overstory composition |
Douglas-fir, lodgepole
pine, ponderosa pine, western larch |
Douglas-fir, ponderosa
pine, western larch |
Douglas-fir, ponderosa
pine, western larch |
|
Understory composition |
Douglas-fir, subalpine
fir |
None |
None |
|
Canopy bulk density (kg/m³) |
0.085 |
0.078 |
0.016 |
|
Canopy base height (m) |
6 |
20 |
20 |
|
Canopy fuel loading (kg/m²) |
1.03 |
0.95 |
0.18 |
|
Surface fuel load (kg/m²) |
8.34 |
1.13 |
1.17 |
|
Surface fuel depth (m) |
1.1 |
0.1 |
0.4 |
|
Fine fuel moisture (%) |
4 |
4 |
4 |
|
Temperature (°C) |
28 |
28 |
28 |
|
10m windspeed (km/h) |
34 |
34 |
34 |
|
Midflame windspeed (km/h) |
3.2 |
12 |
12.8 |
|
Slope (%) |
10 |
10 |
10 |
|
Model Outputs |
|
|
|
|
Rate of spread (m/min) |
3.4 |
2.6 |
42.9 |
|
Fire type |
Surface |
Surface |
Surface |
|
Crown fraction burned |
0 |
0 |
0 |
|
Elliptical fire size in 1 hour (ha) |
2.4 |
1.4 |
163 |
The modeling comparison in Table 4 is used to illustrate a number of key issues relative
to fuel treatments. First and foremost is the effect of the treatment on the
fire environment: the wind, temperature, humidity and fuel moisture. In the
anal
With a decrease in
overstory density, temperature would increase, relative humidity would
decrease, and windspeed would increase at the surface fuel level. Windspeed at
the level of the flames, referred to as midflame windspeed, was allowed to
change as stand structure changed. The effect of fuel treatments on wind is a
key issue in prescribing fuel treatments.
In fire behaviour modeling,
the effect of wind friction, caused by vegetative cover, must be incorporated
into the model and is referred to as the Wind Adjustment Factor. A strong
empirical relationship has been established between wind friction, surface fire
rate of spread, and midflame windspeed. As can be seen in Figure 25 and in the comparison of fuel treatments in Table 4, with decreasing wind friction both midflame
windspeed and rate of spread increase. This can be an unintended consequence of
interface fuel treatments. Significantly reduced tree density, often the intent
of interface treatments, will certainly reduce the likelihood of a crown fire,
however, this same treatment objective, if it results in significant grass
growth, will decrease surface fuel moisture and increase surface fire spread
rate (van Wagtendonk 1996, Edmonds et al. 2000).
The heavy overstory thin
alternative was modeled based on a tall, dense grass response due to the
increased light and moisture reaching the forest floor. This fuel complex lends
itself to rapid seasonal curing and, when ignited, very rapid rates of spread.
The light overstory thin was modeled based on a more prostrate grass response
as would be found with sedges (Carex
spp.) and pinegrass (Calamagrostis
rubescens) growing under low light situations, or situations where grasses
are frequently grazed. These shallower grass fuel complexes result in much
slower rates of spread.
From the perspective of
which of the three fuel strata to concentrate on, researchers are suggesting
that surface and ladder fuels should take priority over extensive crown
thinning (Edmonds et al. 2000, Graham et al. 2004).
Another key issue relative
to fuel treatments has to do with the intensity of the treatment from an economic
perspective. A cost-benefit analysis was not part of this modeling exercise;
however, it is fairly evident to see that the only treatment that could
possibly pay for itself would be the heavy thin treatment. A large proportion
(87%) of the overstory was removed with this treatment relative to the light
thin (20%). It is questionable, however, whether the increased economic gain
would be positively offset by the increased risk of high-intensity fire. This
is a significant issue in the current environment of little to no
provincial-level fuel mitigation funding, especially as it relates to treatment
funding incentives and opportunities for private and municipal lands.
Without a provincial
funding source with standards of practice (Best Management Practices) attached
to the funding, private and municipal land owners are left to devise creative
and potentially damaging alternatives to fuel hazard reduction. Our three
treatment alternatives in Table 4 provide a good illustration of this issue.
A municipality with no
budget for fuel hazard mitigation but a significant area of hazard has two
alternatives for management: (1) the low-intensity thinning and surface fuel
clean-up, which would likely cost several hundred to possibly several thousand
dollars/ha, or, (2) the heavy overstory thin and surface fuel clean-up which
could produce several thousand dollars/ha in revenue. In the short term (which,
with civic or provincial-level politics is a significant but immeasurable
confounding effect) and from a strictly economic perspective, the latter
alternative appears to be the best option. A cash-starved municipal government
could at best set-up a long-term fuel-treatment trust fund with the revenue, or
at worst, sink it into general revenue.
However, longer-term
effects and perspectives beyond simply economics suggest that the former
alternative may be the best option. An infusion of dollars could produce a
stand structure that is resilient to fire, safe for firefighters to work in
(both municipal and provincial), has increased in economic value (providing
options for future economic gain), and will cost little to maintain (see Arno
and Allison-Bunnell 2002 for a good description of restoration forestry
alternatives on private land). Unfortunately, the influence of larger economic
returns versus investments will prevail in many cases resulting in increased
fuel hazards on private and municipal lands.
The effect of fuel
treatments on the fuel complex, fire environment, and fire behaviour can also
have unintended consequences for the local fire suppression organization’s
ability to successfully suppress a fire. The principle reaction to the fires of
2003 has been the desire to significantly thin the forests in the WUI zone.
While this may look promising from economic and risk reduction perspectives
(looking solely at wood volume removed), it may cause innumerable problems for
local suppression agencies and associated municipal governments.
Figure
25.
Graphical representation of the effects of tree thinning on windspeed and fire
behavior. Fire spread rate and the windspeed at the height of the fuel bed
(midflame windspeed) are modeled on the following conditions: timber litter
with grass fuel type; fine fuel (<7.5cm diameter) moisture content <6%;
10m windspeed of 20km/h; and, slope of 10%.
The model results in Table 4 also point out the difficulties that municipal fire
departments face in equipment, resources, and training; all elements that may
need to be reviewed in light of significant interface area treated. Fast moving
surface fires require rapid responses; something that can be difficult for
volunteer fire departments. Not only is continued access after the treatments
an issue but fire discovery and action can take time.
Even though the fires being
described in Figure 25 are grass fires with high rates of spread the fire area, and more
importantly the fire perimeter (the actual part of the fire being suppressed),
can overwhelm local initial attack resources. Transitioning the traditional
municipal fire department’s role from structure protection to structure
protection/wildland fire protection can be very costly to small, municipal
governments. New equipment and additional human resources may be necessary, and
an increased emphasis on cross-training for the new mission may also be
required.
An increase in fire load
will likely accompany any changes in municipal fire agency logistics and infrastructure.
Throughout much of the southern interior the local municipal fire departments
bear the brunt of the early spring grass fire season. Provincial assets are not
usually available until May and begin to depart once again by late September.
If large areas of interface are heavily thinned and converted to grass the
early season workload of municipal fire departments could increase
substantially.
The third major issue to
consider with interface fuel treatments is the useful life of the treatment. If
the treatment is only going to be beneficial in reducing fire behaviour for a
year, the initial treatment strategies should be reviewed or follow-up
treatments should be scheduled. A significant part of this issue is the need to
predict the vegetation response to the initial treatment. In the heavy thin
alternative in Table
4 the significant increase in sunlight reaching the
forest floor will likely result in a substantial understory response; in the
modeling exercise tall grass was assumed to be the primary benefactor of
increased light and moisture. Regenerating conifers are also likely to be an
issue a few short years after the treatment, especially if the treatment
results in extensive ground disturbance. The resultant high-density understory
layer of sapling conifers can constitute an extreme fire hazard and can be very
expensive to mitigate (Gray 2003, Gray 2004). The lighter thin alternative may
not result in an appreciable regeneration response, the response may be limited
in density, and height growth may be slow enough that remedial treatments would
be infrequent and relatively inexpensive.
A significant confounding
issue with the life span of the treatment, intensity of treatment, and
vegetation response is the current regulatory land-use environment that
requires regeneration on public forest lands. This is likely to create a
disincentive for larger licensees to operate in the WUI and create significant
costs and hazard-related liabilities for small-scale licensees such as
Community Forests and Woodlots. For small-scale license holders whose cutting
rights are located in the WUI, the issue is getting the rate of cut
commensurate with the rate of hazard reduction. If the entire small-scale
license area is considered to be hazardous the resolution of the hazard will
not conform to the traditional Long-Run Sustained Yield (LRSY) model.
Conforming to this model would result in the problem being addressed a little
each year instead of quickly being mitigated. Unfortunately, this model also
requires the licensee to regenerate the stand. Not withstanding other
significant economic issues such as the intensity of thinning, thinning
under-valued trees, and post-thinning fuel treatments, the resolution of WUI
fuel hazards cannot be met using the traditional LRSY model as imposed on
small-scale licensees.
5.5 Prescribed fire
Historically in B.C., fuel
management, specifically the use of prescribed fire, has been used for hazard
abatement, wildlife habitat enhancement, and as a silviculture tool used to
prepare the site for planting. Prescribed fire has been identified by many
stakeholders in the province as a beneficial tool for resolving fuels and
wildfire threat (Filmon 2003). However, two issues have plagued the practice:
1) inconsistent funding for burn programs, and 2) failure of prescribed burns
to meet stated objectives (fires escaped, fire and burn severity beyond
prescribed, did not consume enough material, etc.). These issues are seen as
significant impediments to the widespread acceptance and use of prescribed fire
in B.C.
Prescribed fire is constrained by two types of objectives: 1) the area
objective (keeping fire impacts limited to a predetermined area), and 2) the
ecological objectives (ecologically appropriate, attainable and compatible,
tied to long-term management goals, part of integrated resource planning,
quantitative, measurable, and monitored). Meeting burn objectives is dependent
on well-trained and qualified burn teams. The proposed MOF prescribed burn boss
qualification (http://www.for.gov.bc.ca/protect/burning/planning.htm#cert
system does not adequately provide training in the disciplines of fire ecology,
fire behaviour, and prescribed fire ignition operations. Making accurate and
timely predictions of fire behaviour and fire effects is key to safely and
effectively carrying out successful prescribed burns.
Multiple benefits to fuels
and wildfire hazard reduction in the dry forests of B.C. can be achieved with
an expanded provincial prescribed fire program that utilizes both public and
private resources. However, the knowledge, experience, and ability to deliver
on such a program is currently limited in B.C.
The government must also
set clear standards for burn plan contents. These should include a clear presentation
of the fire environment and fire behaviour necessary to meet the burn
objectives, and how the objectives will be monitored. The burn plan and
monitoring results will then form the basis for any post-activity audit.
Tools developed in Canada
for the prediction of fire behaviour and fire effects (e.g., Prescribed Fire
Predictor) have focused almost entirely on either clear-cut slash situations or
stand-replacement fire. These tools and decision aids require significant
improvement in accuracy and/or resolution to improve prescribed fire planning
and prediction.
In many of our fire prone
ecos
5.6 Forest health and its relationship to fuels
Forest health was defined earlier in this report as biotic and abiotic
influences or factors on a forest that have an adverse effect on the health of
trees and other plants. Forest health
treatments are the application of techniques to influence pest or
beneficial organis
Forest health management practices can influence the amount of fuels
associated with insect and disease activity. These management practices must
incorporate other resource concerns (including those outlined in Land and
Resource Management Plans (LRMP) that can compromise the effectiveness of
treatment programs, such as, the inability to remove or treat trees infested
with bark beetles within riparian zones (width varies by stream
classification); these trees are often of larger diameter than surrounding trees
and support a large population of beetles.
Similarly, insect and disease management in the Douglas-fir landscape
may be impeded by other resource concerns. Depending on the local LRMP,
restrictions such as cutblock size, species and ageclass may lead to higher
losses (mortality) and therefore higher fuel hazards. Western spruce budworm
outbreaks within this ecosystem cause understorey mortality, with the
multi-layered Douglas-fir stands suffering the greatest impacts.
Douglas-fir dwarf mistletoe also flourishes in multi-layered single
species stands. The brooms associated with this mistletoe can be very large and
provide for either ladder or ground fuels. Other forest health activities that
contribute to fuel loading include slashing of residual/advanced regeneration
that were greater than 2 metres tall in areas with dwarf mistletoe(s). This
practice is particularly widespread for lodgepole pine dwarf mistletoe as it is
the most prevalent mistletoe species in the province.
An estimate of insect attack-related
fuels was generated for a short list of bark beetles active in the southern
interior of B.C. The spatial extent of their activity over the last twenty
years is illustrated in Appendix 3. By far the most noteworthy of these pests
is the mountain pine beetle with the current estimate of infested area in the
province standing at close to 7 million hectares (Figure 14). It is expected that large areas of this infestation
will not be harvested (Ministry of Forests 2004) ultimately leading to large
areas of dead and downed material. The relationship between the less obvious or
noteworthy pests and forest fuels, or between forest health agents and forest
health treatments and fuels, is less clear.
As applied in B.C., forest health treatments typically focus solely on
the insect or disease pest with little secondary consideration for the
treatment effects on fuel hazard (Figure 26). This indicates a biased interpretation of forest
health agent or factor as being of biotic origin. The abiotic influences or
processes of fuel and fire are not part of the forest health lexicon. For
example, the typical suite of insect control tactics includes pesticides,
sanitation cutting and removal, and fall and burn. Chemical control strategies
specifically target the host tree or the insect itself with the death of the
host tree – and subsequently the insect – being the best result. The secondary
result in this strategy is the future input of surface fuels. While at small-scales
this is not likely to contribute to a substantial fuel hazard, at larger scales
it does contribute to a hazard.
Figure
26.
Before and after photographs of an area of forest health treatment. The
treatment involved salvaging as much merchantable material as possible but did
not include a fuel treatment. The large remaining density of small-diameter
trees is future surface fuel (Photos by R. Gray).
The focus of beetle
management is on the economics of recovering as much value as possible from the
dead or soon to be dead lodgepole pine before decay makes the wood
uneconomical. The fuels and wildfire implications of the hundreds of thousands
of hectares of both treated and untreated lodgepole pine has received scattered
(e.g., LRMP group in Vanderhoof) but not widespread attention in the province.
To some, the large, landscape-scale expanses of dead lodgepole are considered
to be mimicking a natural disturbance (Figure
27), while at the stand-level the large quantities of
dead pine – either naturally generated or human-generated – are considered to
be natural accumulations of CWD (Ministry of Forests 2004).
Figure 27. Large-scale
infestation of mountain pine beetle with characteristic “red attack” lodgepole
pine (R. Gray photo).
5.7 Biodiversity management and its relationship to fuels
Most definitions of
biodiversity include three distinct components: composition, structure, and
function. The compositional component represents the variety of fauna and flora
within an area. The structural component refers to the arrangement of fauna and
flora, including their spatial and age-class distribution. The functional
component characterizes the processes and mechanisms occurring within an
ecosystem including, but not limited to, nutrient cycling, decomposition, and
energy flows (Franklin 1988, Oliver 1992, West 1994, Pregitzer et al.
2001).
Biodiversity can be
increased by fire, and reduced by eliminating fire, in many ecosystems.
Variability of fire regimes in time and space creates the most diverse
complexes of species. Thus, landscapes having fires with high variability in
timing, intensity, pattern, and frequency tend to have the greatest diversity
in ecosystem components. The phrase “pyrodiversity promotes biodiversity” aptly
summarizes this concept (Brown 2000). However, biodiversity can be reduced when
fires occur much more frequently than under the historical regime, or when fire
severity is departed from the historic regime. The task for resource managers
required to manage for biodiversity is to either preserve biodiversity through
static set asides, or to promote biodiversity through restoration efforts in a
dynamically-managed landscape (Everett et al. 1996, Everett et al.
1998, Everett and Lehmkuhl 1999).
Biodiversity
management in British Columbia has for the most part focused on biodiversity protection through a series of static, or near static[9],
reserves (Ministry of Environment, Lands and Parks and Ministry of Forests
1995) (Figure 28), and is employed at two scales: (1) stand-level attributes
(e.g., CWD, Wildlife Tree Patches), and, (2) landscape-scale aggregations of
attributes. Examples of landscape-scale reserves include Old Growth Management
Areas (OGMAs), Riparian Reserve Zones (RRZs), Special Resource Management Zones
(SRMZs), and Parks and Protected Areas. Passive management of processes and
ecos
Figure
28.
A graphical example of the collision between static reserves and dynamic ecological
processes. The 2003 Okanagan Mountain Park Fire is outlined in red while a
number of reserve designations are overlayed on the burn perimeter. The
attributes that made each of these reserves important have all been
significantly degraded because of the changed fire regimes.
From the context of fire
regime departure it can be argued that the greatest threat to many biodiversity
reserves actually comes from wildfire and its subsequent environmental effects.
This hypothesis is illustrated in the following section using two reserve
designations as case studies: riparian reserves and Parks and Protected Areas,
both are examples of landscape-scale aggregations of attributes. A stand-level
attribute – CWD – was addressed in Section 3.3.1. In this section Parks and Protected Areas are used
as a corollary for a number of similar reserves such as OGMA, SRMZ, WTP, and
5.7.1 Riparian Reserves
It is often attractive to
promote a strictly static management approach to ecosystem components that have
been detrimentally affected by past natural resource management. Riparian
systems are a good example of this. A long history of human use in and adjacent
to riparian systems (e.g., dams, irrigation, diking, logging, grazing) has
resulted in a simplification of what are naturally very complex systems (Naiman
et al. 1992; Voller 1998).
Given the landscape-scale
threat from wildfire, whether or not a static or passive approach to riparian
system management is appropriate should be considered; especially in our dry,
fire prone forest types. An alternative to the current regulatory framework
that advocates passive management is a strategy that employs fire regime
information to guide the location, frequency, and intensity of active forest
management in riparian systems. This strategy is based on the assumption that
species have adapted to a certain range of ecosystem conditions brought about
by natural disturbance regimes, and that human activities that maintain
ecosystems within this range may increase the potential for sustaining
ecological processes and native biological diversity (Tollefson et al.
2004). Research has shown that: fire historically had a varying impact on
riparian systems based on landscape location; riparian systems throughout the
west contain unnaturally high accumulations of fuels due to fire exclusion,
and; the effects of unnaturally severe wildfires have extensive long-term
impacts on riparian system sustainability and diversity.
The study of riparian
system natural disturbance regimes has focused in large part on hydrologic
impacts due to geomorphological processes (Dunne and Leopold 1978), while
contemporary disturbance regime studies have focused on the hydrologic impacts
of forest management activities (e.g., logging, road building). Recent interest
due to large-scale wildfires has focused on the effects of fire as a natural
process on riparian system hydrology and vegetation (Minshall et al.
1997; Scott and Pike 2003; Wondzell and King 2003). Few studies, however, have
attempted to determine the relationship between historic natural fire regimes
and riparian systems.
It may be assumed that fire
frequency was historically very high for certain dry forest types in the west
while the opposite would be true for riparian systems with their inherently
higher moisture conditions. However, recent studies in the Klamath Mountains of
northern California (Skinner 2003), western Cascade Mountains of central Oregon
(Tollefson et al. 2004), and the eastern Cascade Mountains of Washington
(Everett et al. 2003) have yielded evidence that fire’s relationship to
riparian systems is more complex than originally thought. Working with mostly
steep-gradient, lower order stream systems the authors found that, as stream
gradient increased in slope and decreased in width, the correlation between the
fire regime within the riparian corridor and the adjacent upland site
increased. Conversely, as slope gradient decreased the riparian width increased
and fire regime differences increased.
Reasons for this pattern
are fairly obvious from a fire behaviour perspective. Riparian vegetation,
including the understory community, is assumed to act as a firebreak; a
moisture barrier to fire spread. This is certainly true for very wide riparian
corridors on flat ground (Skinner 2003). Very narrow stream corridors on steep
terrain, however, do not contain adequate surface fuel moisture or fuel types
to stop most fires (Everett et al. 2003; Skinner 2003; Tollefson et
al. 2004). Historically, many natural fires occurred in the late summer and
early fall when stream flow was at its lowest. As the water table beneath the
riparian corridor diminishes, the vegetation within this zone begins to cure
and surface fuels dry. For very wide riparian systems this means that a fire
may run into riparian vegetation a short distance before hitting an
insurmountable moisture barrier. Narrow riparian corridors may experience
intermittent stream flow during these seasonal periods causing riparian
vegetation and fuels to dry to the point where they will carry a fire.