Grantee Research Project Results
Final Report: Multi-scale Effects of Forest Fragmentation and Landscape Context on Population Health of Birds
EPA Grant Number: R827673Title: Multi-scale Effects of Forest Fragmentation and Landscape Context on Population Health of Birds
Investigators: Martin, Thomas E. , Redmond, Roland L.
Institution: University of Montana
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1999 through September 30, 2002 (Extended to September 30, 2003)
Project Amount: $659,331
RFA: Regional Scale Analysis and Assessment (1999) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
The objectives of this research project were to: (1) develop a matrix population model based on the life cycle of passerine and picid birds that accurately predicts population growth rate and fitness from demographic data; (2) use data from intensive studies of avian demography at replicated sites (from the Breeding Biology Research and Monitoring Database [BBIRD]) and multiple spatial scales within and among geographic regions to assess the effects of forest fragmentation at different spatial scales on nest predation and brown-headed cowbird (Molothrus ater) parasitism; and (3) analyze random samples of forested landscapes across the continental United States to evaluate how well the BBIRD study sites represent overall forest conditions, examine the scaling relationship between forest area and increasing radial distance, and measure the similarities and differences between eastern and western forests.
Summary/Accomplishments (Outputs/Outcomes):
Modeling Avian Population Growth
We developed a three-stage matrix population projection model to represent the life cycle of passerine and picid birds, and to provide a means for computing population growth and fitness from demographic data (Clark, et al., in revision, 2004). Model simulations indicate that nest success and juvenile survival regulate population growth in a wide range of passerine species. Our simulations suggest that landscape alteration affecting breeding habitat has more impact on population growth than changes in adult survival among neotropical migratory bird species. The results provide a foundation for larger scale applications of this model of the passerine life cycle. The next step is the application of the model to populations in diverse geographic areas across North America to quantify the effects of landscape and larger level scale variation in reproductive success on the population dynamics of neotropical migrants. Linking landscape patterns to the variation in breeding success will provide a means for testing the effects of breeding habitat fragmentation on population growth and viability for different passerine life history strategies. In August 2002, a manuscript was submitted to Ecology. This manuscript currently is being revised for resubmission (Clark and Martin, in revision, 2004).
Multiscale Effects of Forest Fragmentation
At landscape scales, ovenbird nest parasitism rate and daily nest predation rate correlated positively with the extent of forest fragmentation, particularly within a 5-10 km radius of study plots. The results emphasize the overwhelming influence of landscape context over edge effects, especially on nest parasitism rates. Given the extensive published evidence of edge effects on nest predation in particular, we highlighted the importance of considering the effects of forest fragmentation on patch-specific demography within a top-down spatial hierarchy (Lloyd, et al., in review, 2004).
Spatial scale is a critical determinant of the effects of forest fragmentation on ecological processes (nest parasitism, predation). Incorporation of these scale effects shows that forest fragmentation is causing broad negative impacts on the population growth potential of a variety of forest-nesting bird species. We used replicated studies across 30 landscapes to show that nest parasitism is affected by fragmentation, particularly at 5-20 km radius scales. In contrast to many published studies conducted in a single location, we found that nest predation was minimally affected by fragmentation, and the effects occurred at finer spatial scales (Lloyd, et al., 2004). Fragmentation caused the interaction of these two processes to negatively impact population growth potential for 15 of 17 bird species. Modeling of the relationships between population growth potential and landscape fragmentation permitted mapping of continental landscapes with negative versus positive population growth potential. Maps for two species, the ovenbird and wood thrush, show how the impacts of fragmentation can differ quite remarkably, in a manner consistent with trends from broad-scale survey data collected over the last 30 years. In particular, wood thrushes show declining populations across their ranges, and our modeling indicates that landscapes in much of their range are of types that yield population sinks most frequently. In contrast, ovenbirds have stable or increasing populations across their geographic range and modeling of landscapes across their range shows a high proportion of source populations. Thus, our modeling predicts maps of sources and sinks that fit with long-term population trends across large geographic areas.
These relationships appear to be reinforced by habitat selection patterns. We related continental patterns of ovenbird and wood thrush abundance (from North American Breeding Bird Survey data) to the average proportion of developed land cover. We found that ovenbirds strongly avoid landscapes with high proportions of developed land cover (r = -0.41, P < 0.001, n = 609), where their fecundity tends to be low; this reinforces their stable or positive population growth trend. In contrast, wood thrushes only weakly avoid landscapes with high proportions of developed land cover, such that only 1 percent of the variation in wood thrush abundance was associated with landscape fragmentation (r = -0.10, P < 0.005, n = 861), which reinforces the negative population trend observed for this species. Predictive mapping efforts such as these can help to identify and prioritize areas for conservation and more effective management.
Fragmentation Characteristics of Forested Landscapes
We found little difference between cumulative distribution functions (CDFs) generated for the proportion of forest area and proportion of forest core area within increasing radial distances of both the BBIRD and randomly selected forested sites across the continental United States. From this, we conclude that BBIRD sites provide an unbiased representation of the extent of fragmentation within the Eastern and Western United States. The CDFs further suggest that the Eastern United States has not only a higher proportion of forest, but a lower degree of fragmentation (i.e., more core area) than the Western United States. In fact, nearly all metrics we examined suggest that the West is relatively less forested—and more fragmented—than the East. In general, we found that as larger areas are examined, forests appear increasingly fragmented. This trend is most evident for the Western United States, and may reflect, in part, historically more patchy forest distribution than in the Eastern United States, where environmental factors allow for relatively contiguous forests across broad areas.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 8 publications | 3 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Clark ME, Martin TE. Modeling tradeoffs in avian life history traits and consequences for population growth. Ecological Modelling 2007;209(2-4):110-120. |
R827673 (2002) R827673 (Final) |
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Lloyd P, Martin TE, Redmond RL, Langner U, Hart MM. Linking demographic effects of habitat fragmentation across landscapes to continental source-sink dynamics. Ecological Applications 2005;15(5):1504-1514. |
R827673 (Final) |
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Supplemental Keywords:
ecosystem, indicators, regionalization, scaling, terrestrial, habitat, integrated assessment, public policy, decisionmaking, observation, public good, conservation, environmental assets, biology, ecology, zoology, modeling, monitoring, analytical, surveys, measurements methods, satellite, Landsat, remote sensing, eastern, western, forest, forest fragmentation., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Forestry, Environmental Monitoring, Regional/Scaling, Biology, landscape context, population sensitivity, demographic consequences, regional scale impacts, birds, agriculture, habitat protection, remote sensing imagery, parasitism, forest fragmentationRelevant Websites:
http://pica.wru.umt.edu/BBIRD/ Exit
http://cornell.birdsource.org/BBIRD/Reports Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.