This factsheet will focus on how fire affects domestic livestock and wildlife including immediate effects (direct) and long-term effects (secondary). These effects will vary depending on fire type, timing, size, severity, and intensity and while direct effects can be significant, secondary effects generally have the greatest amount of impact on livestock and wildlife. In general, fire effects on livestock and wildlife are either:
IMMEDIATE
EFFECTSAnimals: Most livestock and wildlife are directly impacted by a fire and respond relatively predictably to its passage. The degree of impact is dependant on numerous factors including mobility as well as fire uniformity, severity, size and duration. Even though relatively few livestock and wildlife are directly killed or injured by fire, it can and does happen. Various deaths and injuries were reported following British Columbia’s 2003 fire season including cattle mortality, hoof (cattle), and paw (black bear) injuries as well as other injuries such as burned udders.
In general, an ambient temperature of over 63 oC is needed
to result in animal mortality. While most fires have the potential
to injure and kill animals it is generally season of burn and fire
intensity and severity that determines whether or not this occurs.
Season of burn can be an important variable in determining
mortality. For example, a fire that occurs when animals are nesting
or have young with limited mobility (especially small mammals) may
cause significant mortality. This effect would be dependant on
nesting characteristics, with those species who construct
surface-level nests (harvest mice, woodrats) being more vulnerable
to fire than deeper-nesting species. Generally, when compared to
other species smaller mammals, such as mice and voles, due to their
limited mobility, are more vulnerable to fire. Livestock and larger
mammals, due to their size, must escape a fire by seeking refuge,
either in an unburned patch within a fire or outside the extent of
the fire. They are more likely to be caught in a fire when the fire
is actively crowning, its fronts are wide, and it is fast moving
with thick ground smoke present. For example, the large fires of
1988 in the Greater Yellowstone area killed about 1 percent of the
area’s total elk population, with most of these deaths being
attributed to smoke inhalation. When subjected to fire, some studies
have observed that small animals appear to panic more readily than
large, highly mobile animals. In fact, larger mammals are often
described as moving calmly around the fire perimeter. For example,
in Smith (2000) no large mammals were observed fleeing the
Yellowstone fires, with most appearing “indifferent” even to
crowning fires. In fact, some species including bison and elk were
described as grazing and resting within 100 meters of burning trees.
The 2003 British Columbia wildfires did result in livestock
mortality north of Kamloops. The picture on the left shows cattle
carcasses found following the McClure wildfire.
Plants:
Fire also impacts forage availability by directly consuming plant
material. Thus, when considering the effect of fire on all forms of
livestock and wildlife, it is important to consider the lag in
forage availability. For example, if a fire occurs during late
summer or fall, forage availability in the burned areas will often
be non-existent or decreased significantly until at least the
following growing season
Forage Productivity- Increased productivity tends to be short-lived and generally results from a variety of factors including, fire-induced vegetative reproduction and regeneration, fire-enhanced seedling germination and establishment, improvements in soil nutrient regime, and increases in soil temperature. There are numerous benefits associated with increased productivity. These include increased forage productivity (due to canopy removal and nutrient increases) which can benefit mammals by increasing habitat availability. For example, increased productivity can facilitate population dispersal of bighorn sheep which may subsequently result in a reduced incidence of lungworm infections. Most of the productivity research has revolved around tree, grass, and forb productivity.
Trees and Shrubs- The growth of many shrubs and trees is often facilitated by fire. Examples include Saskatoon, chokecherry, mock orange, snowberry, rabbitbrush, paper birch and aspen.
Forbs - The effect of fire on forb productivity appears to be highly variable and dependant on a variety of factors including, fire-induced vegetative reproduction and regeneration, fire-enhanced seedling germination and establishment, improvements in soil nutrient regime, and increases in soil temperature. Examples of increased production exist throughout the literature. For example, one study found total herbaceous production to average 2.2 times higher on burns compared to controls (two to three years after burning). The author of this study however, didn’t attribute this increase solely to the fire. Mesic site conditions and specific plant competitive characteristics were also hypothesized as causing this increase. Other studies have also found fire-induced growth to exceed, both pre-burn and not burned levels. This effect however, is generally short-lived, often disappearing by the second year, and may often be caused by above average precipitation. Finally, other studies have found the production of numerous species, including western yarrow, longleaf phlox, and purple daisy fleabane, to double within three to four years following fire. This increase continued even after twelve years (following the fire), where total forb production was still found to be considerably higher on all burn intensities when compared to areas that were not burned. Numerous rhizomatous perennials accounted for this increase including western yarrow, Aster sp., fleabane, and goldenrods as well as other forbs including little-leaf pussytoes and sticky geranium (especially on light and moderate burns).
Grass - The effect of fire on grass productivity is also variable. For
example, studies have found the production of burned bluebunch
wheatgrass, on sites in the Pacific Northwest, to increase by 24%,
whereas others have only showed minor changes. Furthermore, others
have reported initial declines in bluebunch wheatgrass production of
up to 50%, with recovery time ranging between three and 12 years.
Reduced productivity can result from a variety of factors including
plant mortality, reduction in basal area of grasses, forbs, and
shrubs, changes in species composition to less productive plants,
and reduced availability of soil nutrients. These changes are
generally short-term and dependent on the relationship between
species involved, fire intensity and severity.
In addition to those mentioned above, increases in productivity may also be related to pre-burn site condition and reduced competition. For example, increased herbaceous production is described as increasing most often on range sites in high fair or better range condition (e.g., presence of large bunchgrasses) whereas others have attributed increases to reduced competition. That is, in some areas the elimination of big sage in perennial shrub-steppe grassland has increased grass production by 155% the following summer after the burn and 336% during the second summer. It is important to recognize however, that the precise influence that reduced competition had on these studies was unclear.
Forage Availability- Besides considering the direct effect that fire has on forage availability (see above), fire can also have secondary impacts on forage availability. For example, if a fire occurs early in the growing season, forage will not only be available in the same year as the fire, it may also hold its quality longer into the late summer and fall. The removal of vegetative cover (including trees and shrubs) by fire can also increase snow crusting and accumulation, both of which may reduce forage availability. For example, wind crusting of snow has been described as a common problem on some deer winter ranges. Snow accumulation was also described as increasing on some burns, when compared to areas not burned. The significance of this accumulation however does reduce, due to wind scour, when burn size exceeds approximately four times the height of surrounding tree cover. In general, fire will increase forage availability by:
Livestock Management - In addition to the immediate loss of forage; the availability of livestock forage is also commonly reduced during the first growing season following a fire. This reduction is primarily a management decision needed to accelerate plant recovery following a fire. For more information, please see Factsheet 6 of the Fire Effects on Rangeland Factsheet Series.
Forage Quality- Most of the research centered on forage quality has revolved around grasses and forbs. Shrub forage quality has been largely overlooked and as a result has been purposely excluded from this section. The effect of fire on forage quality is variable and determined by seasonality, species involved and the pre-fire condition of that species. For example, crude protein of bluebunch wheatgrass and various forbs averaged 60% higher on burned sites. These increases however, were generally short-lived, lasting less than two years and were significantly higher in the first year following the burn when compared to the second year. In general, most improvements in forage quality can be attributed to earlier growth, increased rates of growth, and delayed senescence. For example, enhanced growth generally improves forage quality by increasing readily digestible cell solubles relative to cell wall constituents. Furthermore, decreases in forage quality after two years may be attributed to increases in plant density, as density often forms an inverse relationship with forage quality in many plant communities. Overall, since animals have the ability to feed selectively, it is often unreliable to relate improvements in forage quality directly to improvements in animal diets. Feed selectivity may dramatically improve the nutritional makeup of an ungulates diet which otherwise would be severely underestimated by looking at improvements in the forage alone. However, it appears that fire-induced changes in forage quality may benefit ungulates by creating two distinct flushes of nutritious plant tissue in the spring and fall and thus shorten periods of nutritional deprivation.
Animal Performance
Livestock- Exactly how fire influences animal performance is still relatively unknown and there appears to be no data in British Columbia that confirms that the preferential use of burned grasslands by grazing animals will result in measured, increased animal performance. Any improvement in livestock performance is generally dependant on management and the amount, quality and availability of the forage produced following a fire and the forage quality throughout the grazing season.
Ungulates - Studies often contradict one another and practices such as prescribed burning do not always correlate to increased bighorn sheep populations. Prescribed burning in fact may actually deteriorate bighorn sheep ranges by reducing total nutrient availability, especially in grasslands with low cation exchange capacities (i.e., reduced ability to hold nutrients). In order for any changes in habitat parameters to be beneficial to the large mammal in question, the improved parameter must have first been somewhat lacking in the pre-fire habitat. That is, if the mammal in question is not limited by forage production, forage quality, or forage availability, and if other limiting factors remain unaltered, fire will not theoretically improve mammal performance or increase mammal populations. Both bighorn sheep and mule deer have been found to utilize burned bluebunch wheatgrass on a Wyoming big sagebrush/bluebunch wheatgrass winter range site significantly more than adjacent not-burned areas.
Predators
and Omnivores - The
response of carnivores to fire is primarily dependant on herbivore
response. That is, if prey populations increase, so will the
population of carnivores. For example, a study highlighted in Smith
(2000), determined that a decline in small mammals following a fire
resulted in a subsequent decline in American badger numbers. Other
predators, such as the pine marten, have been known to be negatively
impacted by fires, as fires are typically detrimental to their prey
and overall habitat. High severity fires that result in fauna
mortality will benefit carnivores and scavengers including grizzly
bears, black bears, coyotes, bald eagles golden eagles, and common
ravens. For example, following the 2003 British Columbia fire
season, black bear were observed feeding on livestock carcasses in the Barriere area. In addition to increased
carcass availability, fire effects on omnivorous mammals, such as
bears, are dependant on how habitat attributes such as other food
sources and bedding sites are affected. For example, bears are often
impacted when den sites are created or destroyed (i.e. increase in
windfalls, hollow trees or destruction of den sites) or forage
availability is increased through the re- sprouting of
berry-producing shrubs.
In general, fire effects on birds are typically secondary in nature. Direct effects are typically dependant on season, fire uniformity, and severity. Due to their mobility, mortality of adult birds is usually considered minor. If the fire occurs during nesting however, nestling and fledgling mortality will occur. In addition to seasonality, severity also determines whether or not nests are damaged. While ground-nesters are vulnerable to most understory fires, canopy nesters can also be injured by moderately to severe surface and crown fires. In general, fire impacts on birds can be summarized by using the following classification system taken from National Wildfire Coordinating Group (2001):
Very little research has measured the effect of fire on reptiles and amphibians. As with other wildlife, the influence of fire on reptiles and amphibians appears to be predominately secondary. That is, the influence of fire on habitat attributes, such as plant species composition and structure, appear to be the primary factor in determining immigration and emigration. For example, species that prefer open sites may benefit and increase following fire whereas species that prefer or tolerate dense vegetation often decrease.
Brown, J.K. and J.K. Smith, eds. 2000. Wildland fire in ecosystems: effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 257 p.
National Wildfire Coordinating Group. 2001. Fire Effects Guide.
Available online:
http://www.nwcg.gov/pms/RxFire/FEG.pdf.
313 p.
Fire Effects on Rangeland Factsheet Series
A Fire Effects on Rangeland Factsheet series has been developed to assist you in assessing and managing rangeland affected by fire. The titles of these factsheets are:
1. Fire Effects on Rangeland Ecosystems
3. Fire Effects on Grasses and Forbs
4. Fire Effects on Tree and Shrubs
5. Fire Effects on Livestock and Wildlife
6. Post-fire Livestock Management
For further information contact:
Darren Bruhjell
Phone: 250 371-6058
Email:
Darren.Bruhjell@gov.bc.ca
Greg Tegart
Phone:250 260-3035
Email: Greg.Tegart@gov.bc.ca
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