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Pacific Southwest Research Station
800 Buchanan Street
Albany, CA 94710-0011
Research Topics Ecosystem Processes
Sierra Nevada Ecosystems
About this Research:
Effects of prescribed burning in the spring on avian communities
Fire is a natural disturbance that can have an overwhelming influence on vegetative structure, biodiversity, productivity, and species composition in a given area. Fuels management programs implemented in ecosystems where fire is an integral component many mimic natural processes to some degree, but are often characterized by parameters that are different from those of the historic fire regime. Landscape changes resulting from forest management practices such as timber harvest and fire suppression in addition to private property and air quality concerns make burning in the spring desirable for meeting fuel management goals. On the other hand, spring coincides with a number of important wildlife activities such as the breeding of forest birds.
The study area consists of nine sites: three unburned as controls, three burned for the first time in at least fifty years, and three sites burned for a second time within six years. Four sites are part of another PSW study, abundance and productivity of forest birds over an elevational gradient, and have been studied since 1995. This study was initiated in 2001 and will be completed by 2004.
Individual birds chose specific places in which to build their nests and this pattern of nest site selection tends to be well conserved within a species. Loss of eggs and nestlings to predators is the primary cause of nest failure and may be (but is not necessarily) related to the placement of the nest. Preferred nest sites are indicated by the choice of specific habitat features disproportionate from their availability in the study area. Introduction of fire may alter the availability nest sites and birds may respond through choosing a different nest site or moving to unburned areas either within or outside of treatment areas. These alterations may have consequences for the productivity of bird populations. In this study, nests of target species are located and monitored until completion. Characteristics of each nest and its surrounding habitat (selection) are recorded in addition to characteristics at random points selected (availability) within the study area.
Alterations to habitats as the result of fire may influence abundance and diversity of bird populations within a given area. Forest litter, shrubs, ground vegetation, logs, and snags are habitat features most affected by low intensity fire. wildlife associated with these features may be reduced temporarily. Specific habitat features do not generally occur evenly across a given area but are patchily distributed. Patchiness or heterogeneity is generally associated with high biodiversity and fire generally increases heterogeneity across the landscape. Avian populations are monitored through a standardized census method consisting of a 1,000 meter timed transect.
Snags are an important aspect of forest structure for wildlife and provide nest and roost sites for a wide variety of cavity-nesting birds and mammals. Fire and snags have a complex relationship as fires may result in the consumption of snags, while at the same time live trees may be killed. Snags are chosen at random at each study site and followed through the course of the study to determine availability as well as natural fall rates and changes associated with burning. Those snags that are actually used by breeding birds are also followed and their features compared to those of random snags.
This study seeks not only to understand how birds respond to a changing landscape, but also to integrate forest management practices with research. Through this integration, we can gain not only a better understanding of the natural world but make informed decisions about fire management.
To monitor population changes in bird populations and species composition in response to prescribed fire.
Methods and Design
The nine study sites are within mature ponderosa pine forests that are part of a prescribed burning program, the Front Country Underburn, being conducted by Sierra National Forest. To achieve specific fuel reduction objectives, fire management plans for the study area call for burning of up to three times in each burn unit with a return interval of 2 to 3 years. Objectives include consumption of 75% of dead and down fuels less than nine inches in diameter and top kill 50 to 80 % of encroaching brush with eventual removal of brush skeletons through multiple entries. Ten hour timelag fuel moisture is the primary fuel parameter used for determining timing of ignition. In this region, these conditions are generally met during the spring when conditions are moist and air temperatures are cool.
Nine sites, approximately 40 hectares each in size, will be located with the Big Creek watershed. Burned sites (six total) will consist of first and second entry sites. Three second entry sites, burned in 1998 or 1999, will be burned a second time in the second year of the study (2002). Three first entry sites will be burned for the first time in the third year of the study (2003). Sites will be matched as closely as possible based on location and habitat. Four of the nine proposed study sites have been studied for 6 years, beginning in 1995, as part of the Kings River Sustainable Forest Ecosystem Administrative Study. These data, which will continue to be collected for the duration of the study, include records of bird species composition and abundance, productivity, nest site selection, characteristics, and local temperature. Data collected by this study will be used in conjunction with his baseline data to quantify conditions relating to fire exclusion and annual variability.
For assessment of avian species composition and relative abundance, census data will be collected using 1000-meter timed transects. All species seen or heard less than 50 meters and outside 50 meters from the census line will be recorded on 6 sampling occasions for each site. Censuses will be conducted annually.
Nests will be located and mapped with emphasis on ground- and shrub-nesting species. Cavity nesters will also be targeted for their association with snag dynamics.. All nests will be monitored every 3 to 4 days to accurately assess nest productivity and outcome. To aide in nest monitoring an extendable camera system (Peeper TM) developed by Sandpiper Technologies will be used to reach high nests and to see inside cavities. Rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater) and nest predation will also be evaluated for possible connections to prescribed burning activity. Predators are often attracted to burns because of the open landscape created which may increase the risk to birds that remain within the burned areas.
Terrestrial salamander communities
Terrestrial salamanders will be monitored through a mark, release, recapture program combined with an artificial cover method on six sites. Placement of cover materials (1'x 1' boards) used for locating salamanders can standardize cover availability and help minimize variation between sites. Surveys will be in accordance with protocols set by the North American Amphibian Monitoring Protocol run by the U.S. Geological Survey. Boards, placed in 2001, are in three grids of 18 boards on each of six sites. Individuals will be marked to better assess populations and to monitor movement patterns. Marking will be done using visible fluorescent elastomer tags (VIE tags), a technique commonly used for fish studies and successfully adopted for marking herpetofauna. A small amount of biocompatible pigment is injected just under the skin in up to four locations to individually identify salamanders.
Bat communities and snags
A snag survey will be conducted to assess snag availability, and to assess loss and recruitment on both burned and control sites. Each snag within a sampling unit will be tagged, recorded, and monitored throughout the study. Snag densities will be collected within each site to monitor changes in snag densities associated with fire. Snags that are used by nesting bird species will be monitored and by recording the location of those snags we will be able to assess their suitability and survival post-fire.
Vegetative characteristics of avian nest sites will also be recorded, and compared across treatments and years to assess changes in habitat selection. Variables associated with nest site selection such as concealment, substrate diameter, and substrate species will be taken at all nests after breeding. Larger scale data on shrub cover, ground cover, canopy cover, and abundance, size, and decay class of logs will be taken for each site within a 0.04 ha circle centered on the nest.
Application of Research Results
We have not found large changes in bird communities related to burning nor were any species clearly restricted to burned or unburned areas. Approximately half of the species examined did not show a response to fire. Changes in bird populations that we found were generally within the range of population fluctuations related to other biotic and abiotic factors in the absence of fire. Additionally, we cannot ignore the fact that without prescribed fires, wildfires will be more intense with greater potential for negative impacts. Thus attempts at fire exclusion do not ultimately benefit those species that have negative responses to fire. Within this context, there is little concern about negatively affecting populations with prescribed fire with the exception of species with low abundance or restricted ranges.
Based on results from this study, we recommend protection of preferred snags, in particular, large ponderosa pines along with the continued reintroduction of fires as an ecological process. Forest management strategies that affect tree species composition, tree mortality, and tree size will affect snag-nesting species. Our results suggest that forest managers can improve availability of useable snags by retaining large trees (both living and dead), and preferred species.
The greatest net loss of snags occurred on sites after long periods of fire exclusion and thus protection of preferred snags may be warranted in these areas if snags are limited. While the characteristics of nesting snags did not affect nesting success, we did find lower nesting success for cavity nesting species immediately following prescribed fire applications.
For open-cup nesters, nesting success was altered by fire for 3 of 5 targeted species. Changes in daily nest survival probabilities due to fire were related to changes to nest site vegetation and only occurred within 1 year of burning. Brood parasitism by Brown-headed Cowbirds increased following fire as long as 6 years postburn. These results are consistent with increased visibility of nests and/or nesting behavior following prescribed fire.
1) Purcell, K.L.; 2) Bagne, K.; 2) Rotenberry, J.
1) USDA Forest Service,
2) University of California
|Last Modified: Jun 13, 2016 04:03:25 PM|