Impacts of Alternative Timber Harvest Practices on Leaf-Chewing Herbivores of Oak

Abstract:  Studies of the effects of logging on Lepidoptera rarely address landscape-level effects or effects on larval, leaf-feeding stages. We examined the impacts of uneven-aged and even-aged logging on the abundance, richness, and community structure of leaf-chewing insects of white ( Quercus alba L.) and black ( Q. velutina L.) oak trees remaining in unharvested areas by sampling 3 years before and 7 years after harvest. After harvest, white oaks in uneven-aged sites had 32% fewer species of leaf-chewing insects than control sites. This reduction in species richness may have resulted from changes in microclimate (reducing plant quality and/or changing leaf phenology) that affected a much larger total area of each site than did even-aged cuts. For black oak after harvest, species richness in uneven- and even-aged sites increased relative to levels before harvest. Harvesting did not alter total insect density or community structure in the unlogged habitat for either oak species with one exception: insect density on black oak increased in the oldest forest block. Community structure of herbivores of black and white oaks in clearcut gaps differed from that of oaks in intact areas of even-aged sites. Furthermore, both richness and total insect density of black oaks were reduced in clearcut gaps. We suggest that low-level harvests alter herbivore species richness at the landscape level. Treatment effects were subtle because we sampled untreated areas of logged landscapes, only one harvest had occurred, and large temporal and spatial variation in abundance and richness existed. Although the effects of logging were greater in uneven-aged sites, the effects of even-aged management are likely to increase as harvesting continues.     

Relation of Terrestrial-Breeding Amphibian Abundance to Tree-Stand Age

There is a lack of research on the effects of logging on Canadian amphibians. We compared the abundance of terrestrial salamanders in old-growth forests with that in young and mature post-harvest stands. We also measured habitat features of amphibians and contrasted these with old-growth and harvested stands to assess the effects of forest harvest. Quadrat searches demonstrated that clearcut harvesting reduces terrestrial amphibian populations by up to 70% in coastal old-growth forests. We suggest that this reduction results from a decrease in availability of moist microhabitats. Salamander densities within 10 meters of streams in managed stands were similar to those near and away from streams in old growth. We recommend that forest managers recognize the needs of terrestrial amphibians and help maintain amphibian populations by preserving cool, moist habitats. This can be accomplished within cutblocks by (1) maintaining an even distribution of logs and snags as stable, moist microhabitats; (2) retaining some understory as sources of shade, and (3) preserving streamside buffers. Managers must also ensure some level of landscape connectivity to enable climate-sensitive amphibians to disperse and recolonize marginal habitats.     

Response of a Reptile Guild to Forest Harvesting

Abstract:  Despite the growing concern over reptile population declines, the effects of modern industrial silviculture on reptiles have been understudied, particularly for diminutive and often overlooked species such as small-bodied snakes. We created 4 replicated forest-management landscapes to determine the response of small snakes to forest harvesting in the Coastal Plain of the southeastern United States. We divided the replicated landscapes into 4 treatments that represented a range of disturbed habitats: clearcut with coarse woody debris removed; clearcut with coarse woody debris retained; thinned pine stand; and control (unharvested second-growth planted pines). Canopy cover and ground litter were significantly reduced in clearcuts, intermediate in thinned forests, and highest in unharvested controls. Bare soil, maximum air temperatures, and understory vegetation all increased with increasing habitat disturbance. Concomitantly, we observed significantly reduced relative abundance of all 6 study species (scarletsnake [Cemophora coccinea] , ring-neck snake [Diadophis punctatus] , scarlet kingsnake [Lampropeltis triangulum] , red-bellied snake [Storeria occipitomaculata] , southeastern crowned snake [Tantilla coronata] , and smooth earthsnake [Virginia valeriae] ) in clearcuts compared with unharvested or thinned pine stands. In contrast, the greatest relative snake abundance occurred in thinned forest stands. Our results demonstrate that at least one form of forest harvesting is compatible with maintaining snake populations. Our results also highlight the importance of open-canopy structure and ground litter to small snakes in southeastern forests and the negative consequences of forest clearcutting for small snakes.     

Effects of landscape design of forest reserves on Saproxylic beetle diversity

Increasing the density of natural reserves in the forest landscape may provide conservation benefits for biodiversity within and beyond reserve borders. We used 2 French data sets on saproxylic beetles and landscape cover of forest reserves (LCFR) to test this hypothesis: national standardized data derived from 252 assessment plots in managed and reserve stands in 9 lowland and 5 highland forests and data from the lowland Rambouillet forest, a forested landscape where a pioneer conservation policy led to creation of a dense network of reserves. Abundance of rare and common saproxylic species and total saproxylic species richness were higher in forest reserves than in adjacent managed stands only in highland forests. In the lowland regional case study, as LCFR increased total species richness and common species abundance in reserves increased. In this case study, when there were two or more reserve patches, rare species abundance inside reserves was higher and common species richness in managed stands was higher than when there was a single large reserve. Spillover and habitat amount affected ecological processes underlying these landscape reserve effects. When LCFR positively affected species richness and abundance in reserves or managed stands, >12‐20% reserve cover led to the highest species diversity and abundance. This result is consistent with the target of 17% forested land area in reserves set at the Nagoya biodiversity summit in 2010. Therefore, to preserve biodiversity we recommend at least doubling the current proportion of forest reserves in European forested landscapes.     

Multi-model analysis of tree competition along environmental gradients in southern New England forests.

Robust predictions of competitive interactions among canopy trees and variation in tree growth along environmental gradients represent key challenges for the management of mixed-species, uneven-aged forests. We analyzed the effects of competition on tree growth along environmental gradients for eight of the most common tree species in southern New England and southeastern New York using forest inventory and analysis (FIA) data, information theoretic decision criteria, and multi-model inference to evaluate models. The suite of models estimated growth of individual trees as a species-specific function of average potential diameter growth, tree diameter at breast height, local environmental conditions, and crowding by neighboring trees. We used ordination based on the relative basal area of species to generate a measure of site conditions in each plot. Two ordination axes were consistent with variation in species abundance along moisture and fertility gradients. Estimated potential growth varied along at least one of these axes for six of the eight species; peak relative abundance of less shade-tolerant species was in all cases displaced away from sites where they showed maximum potential growth. Our crowding functions estimate the strength of competitive effects of neighbors; only one species showed support for the hypothesis that all species of competitors have equivalent effects on growth. The relative weight of evidence (Akaike weights) for the best models varied from a low of 0.207 for Fraxinus americana to 0.747 for Quercus rubra. In such cases, model averaging provides a more robust platform for prediction than that based solely on the best model. We show that predictions based on the selected best models dramatically overestimated differences between species relative to predictions based on the averaged set of models.     

Forest age structure as indicator of boreal forest sustainability under alternative management and fire regimes: A landscape level sensitivity analysis

Effective forest ecosystem-based management requires a thorough understanding of the interactions between anthropogenic and natural disturbance processes over larger spatial and temporal scales than stands and rotation ages. Because harvesting does not preclude fire, it is important to evaluate the combined effects of harvesting and fire on forest age structure, a coarse indicator of forest ecosystem state. We performed a sensitivity analysis of landscape scale effects of forest management (strategy, harvest rate and access cost) and fire regime (fire return interval and extent) in terms of combined impacts on forest stand age-class structure on a study area of 3.5 million hectares of boreal forest of Québec. A series of scenarios were simulated over 500 years and replicated 30 times using a previously reported spatially explicit landscape model. Within the parameter space of our sensitivity analysis, we found that harvest rate, fire return interval and management strategy were the most significant parameters affecting stand age-class distribution across the landscape. The former are not so surprising, given that they combine to produce an overall disturbance rate, but the latter shows that the resulting impact on age-class structure can be influenced to some degree through management objectives. A harvesting strategy of clearcutting for sustained timber supply, using a harvest rotation based on minimum merchantable age (approximately 100 years in this analysis), creates a trend for the stand age-class distribution away from the expected range of natural variation for the study area. Within the scope of our simulations, alternative management strategies with extended harvest rotation age proved the most robust forest management practice to absorb variations in fire regime.     

Applying Principles of Landscape Design and Management to Integrate Old-Growth Forest Enhancement and Commodity Use

Using geographic information systems (GIS) and spatial analysis techniques, we developed a landscape design to maintain old-growth forest remnants and integrate commodity production in the surrounding second-growth matrix. The 4500-ha forest landscape in northern Wisconsin contains scattered patches of old-growth eastern hemlock ( Tsuga canadensis ) and northern hardwoods, predominately sugar maple ( Acer saccharum ). The design incorporates an old-growth restoration zone surrounding old-growth patches to buffer and enhance forest-interior habitat and link nearby old-growth remnants. This addition restores aspects of landscape patch size and structure and ecosystem juxtaposition that characterize a nearby, large, and contiguous natural old-growth landscape. A larger secondary zone is delineated for uneven-aged forest management. This zone provides a matrix structurally similar to the old-growth patches but also accommodates harvesting. A larger outer zone is retained primarily in even-aged forest of aspen ( Populus tremuloides ) and paper birch ( Betula papyrifera ), but traditional clearcutting practices are modified to partial cutting and mixed-species rotations. This design meets limited goals of biodiversity enhancement and integrated commodity production in a landscape that will remain largely harvested. The landscape design is therefore improved not only by buffers and corridors provided to old-growth ecosystems, but by modifying the management of the majority commodity lands matrix as well.     

Two‐Stage Recovery of Amphibian Assemblages Following Selective Logging of Tropical Forests

There is a lack of quantitative information on the effectiveness of selective‐logging practices in ameliorating effects of logging on faunal communities. We conducted a large‐scale replicated field study in 3 selectively logged moist semideciduous forests in West Africa at varying times after timber extraction to assess post logging effects on amphibian assemblages. Specifically, we assessed whether the diversity, abundance, and assemblage composition of amphibians changed over time for forest‐dependent species and those tolerant of forest disturbance. In 2009, we sampled amphibians in 3 forests (total of 48 study plots, each 2 ha) in southwestern Ghana. In each forest, we established plots in undisturbed forest, recently logged forest, and forest logged 10 and 20 years previously. Logging intensity was constant across sites with 3 trees/ha removed. Recently logged forests supported substantially more species than unlogged forests. This was due to an influx of disturbance‐tolerant species after logging. Simultaneously Simpson's index decreased, with increased in dominance of a few species. As time since logging increased richness of disturbance‐tolerant species decreased until 10 years after logging when their composition was indistinguishable from unlogged forests. Simpson's index increased with time since logging and was indistinguishable from unlogged forest 20 years after logging. Forest specialists decreased after logging and recovered slowly. However, after 20 years amphibian assemblages had returned to a state indistinguishable from that of undisturbed forest in both abundance and composition. These results demonstrate that even with low‐intensity logging (≤3 trees/ha) a minimum 20‐year rotation of logging is required for effective conservation of amphibian assemblages in moist semideciduous forests. Furthermore, remnant patches of intact forests retained in the landscape and the presence of permanent brooks may aid in the effective recovery of amphibian assemblages. Recuperación de Ensambles de Anfibios en Dos Etapas Después de la Tala Selectiva de Bosques Tropicales     

Forest structure and light regimes following moderate wind storms: implications for multi-cohort management.

Moderate-severity disturbances appear to be common throughout much of North America, but they have received relatively little detailed study compared to catastrophic disturbances and small gap dynamics. In this study, we examined the immediate impact of moderate-intensity wind storms on stand structure, opening sizes, and light regimes in three hemlock-hardwood forests of northeastern Wisconsin. These were compared to three stands managed by single-tree and group selection, the predominant forest management system for northern hardwoods in the region. Wind storms removed an average of 41% of the stand basal area, compared to 27% removed by uneven-aged harvests, but both disturbances removed trees from a wide range of size classes. The removal of nearly half of the large trees by wind in two old-growth stands caused partial retrogression to mature forest structure, which has been hypothesized to be a major disturbance pathway in the region. Wind storms resulted in residual stand conditions that were much more heterogeneous than in managed stands. Gap sizes ranged from less than 10 m2 up to 5000 m2 in wind-disturbed stands, whereas the largest opening observed in managed stands was only 200 m2. Wind-disturbed stands had, on average, double the available solar radiation at the forest floor compared to managed stands. Solar radiation levels were also more heterogeneous in wind-disturbed stands, with six times more variability at small scales (0.1225 ha) and 15 times more variability at the whole-stand level. Modification of uneven-aged management regimes to include occasional harvests of variable intensity and spatial pattern may help avoid the decline in species diversity that tends to occur after many decades of conventional uneven-aged management. At the same time, a multi-cohort system with these properties would retain a high degree of average crown cover, promote structural heterogeneity typical of old-growth forests, and maintain dominance by late-successional species.     

Assessing Risks to Biodiversity from Future Landscape Change

We examined the impacts of possible future land development patterns on the biodiversity of a landscape. Our landscape data included a remote sensing derived map of the current habitat of the study area and six maps of future habitat distributions resulting from different land development scenarios. Our species data included lists of all bird, mammal, reptile, and amphibian species in the study area, their habitat associations, and area requirements for each. We estimated the area requirements using home ranges, sampled population densities, or genetic area requirements that incorporate dispersal distances. Our measures of biodiversity were species richness and habitat abundance. We calculated habitat abundance in two ways. First, we computed the total habitat area for each species in each landscape. Second, we calculated the number of habitat units for each species in each landscape by dividing the size of each habitat patch in the landscape by the area requirement and summing over all patches. Species richness was based on presence of habitat. Species became extinct in the landscape if they had no habitat area or no habitat units, respectively. We then computed ratios of habitat abundance in each future landscape to habitat abundance in the present for each species. We also computed the ratio of future to present species richness. We then calculated summary statistics across all species. Species richness changed little from present to future. There were distinctly greater risks to habitat abundance in landscapes that extrapolated from present trends or zoning patterns, however, as opposed to landscapes in which land development activities followed more constrained patterns. These results were stable when tested using Monte Carlo simulations and sensitivity tests on the area requirements. We conclude that this methodology can begin to discriminate the effects of potential changes in land development on vertebrate biodiversity.     

Declines in Woodland Salamander Abundance Associated with Non-Native Earthworm and Plant Invasions

Abstract:  Factors that negatively affect the quality of wildlife habitat are a major concern for conservation. Non-native species invasions, in particular, are perceived as a global threat to the quality of wildlife habitat. Recent evidence indicates that some changes to understory plant communities in northern temperate forests of North America, including invasions by 3 non-native plant species, are facilitated by non-native earthworm invasion. Furthermore, non-native earthworm invasions cause a reduction in leaf litter on the forest floor, and the loss of forest leaf litter is commonly associated with declines in forest fauna, including amphibians. We conducted a mark-recapture study of woodland salamander abundance across plant invasion fronts at 10 sites to determine whether earthworm or plant invasions were associated with reduced salamander abundance. Salamander abundance declined exponentially with decreasing leaf litter volume. There was no significant relationship between invasive plant cover and salamander abundance, independent of the effects of leaf litter loss due to earthworm invasion. An analysis of selected salamander prey abundance (excluding earthworms) at 4 sites showed that prey abundance declined with declining leaf litter. The loss of leaf litter layers due to non-native earthworm invasions appears to be negatively affecting woodland salamander abundance, in part, because of declines in the abundance of small arthropods that are a stable resource for salamanders. Our results demonstrate that earthworm invasions pose a significant threat to woodland amphibian fauna in the northeastern United States, and that plant invasions are symptomatic of degraded amphibian habitat but are not necessarily drivers of habitat degradation.     

The importance of defining focal assemblages when evaluating amphibian and reptile responses to land use

Habitat loss and degradation are primary threats to amphibians and reptiles, but the relative effects of common land uses on assemblages and the mechanisms that underlie faunal responses are poorly studied. We reviewed the effects of four prevalent types of habitat alteration (urbanization, agriculture, livestock grazing, and silviculture) on amphibian and reptile species richness and abundance by summarizing reported responses in the literature and by estimating effect sizes across studies for species richness in each land‐use type. We then used a multinomial model to classify species as natural habitat specialists, generalists, and disturbed habitat specialists and examined variation in effect sizes for each land‐use type according to habitat specialization categories. There were mixed conclusions from individual studies, some reporting negative, neutral, or positive effects of land use on species richness and total abundance. A large proportion of studies reported species‐specific effects of individual species abundance. However, in our analysis of effect sizes, we found a general trend of negative effects of land use on species richness. We also demonstrate that habitat associations of common species and species turnover can explain variation in the effect of land use on herpetofauna. Our review highlights the pervasive negative effects of common land uses on amphibians and reptiles, the importance of identifying groups vulnerable to land‐use change (e.g., forest‐associated species) in conservation studies, and the potential influence of disturbance‐associated species on whole assemblage analyses.     

Effects of timber harvesting on pond-breeding amphibian persistence: testing the evacuation hypothesis.

Numerous studies have documented the decline of amphibians following timber harvest. However, direct evidence concerning the mechanisms of population decline is lacking and hinders attempts to develop conservation or recovery plans and solutions for forest species. We summarized the mechanisms by which abundance of amphibians may initially decline following timber harvest into three testable hypotheses: (1) mortality, (2) retreat, and (3) evacuation. Here, we tested the evacuation hypothesis within a large-scale, replicated experiment. We used drift fences with pitfall traps to capture pond-breeding amphibians moving out of experimental clearcut quadrants and into control quadrants at four replicate arrays located within the Daniel Boone Conservation Area on the upper Ozark Plateau in Warren County, Missouri, USA. During the preharvest year of 2004, only 51.6% of the 312 individuals captured were moving out of pre-clearcut quadrants, and movement did not differ from random. In contrast, during both postharvest years of 2005 and 2006, the number of captures along the quadrant edge increased, and a higher proportion of individuals (59.9% and 56.6%, respectively, by year) were moving out of clearcut quadrants than entering. Salamanders moved out of clearcuts in large percentages (Ambystoma annulatum, 78.2% in 2005, 78.2% in 2006; A. maculatum, 64.0% in 2005, 57.1% in 2006). Frogs and toads also moved out of clearcut quadrants, but in lower percentages (Bufo americanus, 59.6% in 2005, 53.3% in 2006; Rana clamitans, 52.7% in 2006). Salamanders moved out of clearcuts with low-wood treatments more than out of clearcuts with high-wood treatments. Movement of salamanders out of clearcuts was independent of sex. Estimated movement out of clearcuts represented between 8.7% and 35.0% of the total breeding adults captured for two species of salamanders. Although we recognize that some portion of the amphibian population may retreat underground for short periods and others may not survive the effects of timber harvest, these data are the first direct evidence showing that individuals are capable of leaving clearcuts and shifting habitat use.     

Effects of Landscape Composition and Wetland Fragmentation on Frog and Toad Abundance and Species Richness in Iowa and Wisconsin, U.S.A.

Abstract: Management of amphibian populations to reverse recent declines will require defining high-quality habitat for individual species or groups of species, followed by efforts to retain or restore these habitats on the landscape. We examined landscape-level habitat relationships for frogs and toads by measuring associations between relative abundance and species richness based on survey data derived from anuran calls and features of land-cover maps for Iowa and Wisconsin. The most consistent result across all anuran guilds was a negative association with the presence of urban land. Upland and wetland forests and emergent wetlands tended to be positively associated with anurans. Landscape metrics that represent edges and patch diversity also had generally positive associations, indicating that anurans benefit from a complex of habitats that include wetlands. In Iowa the most significant associations with relative abundance were the length of the edge between wetland and forest ( positive) and the presence of urban land (negative). In Wisconsin the two most significant associations with relative abundance were forest area and agricultural area ( both positive). Anurans had positive associations with agriculture in Wisconsin but not in Iowa. Remnant forest patches in agricultural landscapes may be providing refuges for some anuran species. Differences in anuran associations with deep water and permanent wetlands between the two states suggest opportunities for management action. Large-scale maps can contribute to predictive models of amphibian habitat use, but water quality and vegetation information collected from individual wetlands will likely be needed to strengthen those predictions. Landscape habitat analyses provide a framework for future experimental and intensive research on specific factors affecting the health of anurans.     

Evaluating the Effectiveness of Corridors: a Genetic Approach

Abstract: The effectiveness of corridors in maintaining dispersal in fragmented landscapes is a question of considerable conservation and ecological importance. We tested the efficacy of corridors as residual landscape structures in maintaining population structure in the red-backed vole ( Clethrionomys gapperi ), a closed-canopy specialist, and the deer mouse (   Peromyscus maniculatus ), a habitat generalist. In coniferous forests managed for timber production in northeastern Washington, we sampled pairs of populations in three landscape classes: (1) contiguous landscapes, in which sites were located completely within a matrix of closed-canopy forest; (2) corridor landscapes, in which sites were connected by a corridor of closed-canopy forest; and (3) isolated landscapes, in which sites were separated from one another by clearcut or young regeneration stands. For each species, we used four microsatellite loci to quantify genetic distance between population pairs. Nei's genetic distance (   D _s  ) increased from smallest to largest in the order of contiguous, corridor, and isolated landscapes for C. gapperi. For P. maniculatus, genetic distances across landscape configurations were not significantly different. The differences between the two species indicate that they respond differently to the presence of forest corridors. In managed forests, corridors between unlogged habitats appear to maintain higher population connectivity for C. gapperi than landscapes without corridors.     

Effects of Buffer-Strip Retention and Clearcutting on Land Snails in Boreal Riparian Forests

Abstract:  We investigated the short-term effects of forest clearcutting on land snails (terrestrial gastropods) in 15 forest stands along small streams in Sweden. Two different silvicultural treatments were applied at each site: clearcutting across the stream channel and buffer strips 10 m wide on each side of the stream. Additionally, we studied 10 reference sites in unlogged riparian forests along similar-sized streams. All sites were studied before logging and then 2.5 years after logging. After clearcutting the number of individuals in a 0.5-m² sample from each site decreased on average from 107 to 87, and the mean number of species per sample decreased from 9.9 to 7.7. Most species were negatively affected, but there were also clear differences in sensitivity. There were correlations between species survival and ground moisture. At the wettest clearcut sites with an almost intact bryophyte cover, the land snails were unaffected by clearcutting. This result suggests that wet or moist forest floors can serve as refugia even at very small spatial scales (e.g., shallow hollows, crevices). If this is an important mechanism, the spatial distribution of small habitats could be important for the long-term survival of the snail fauna or other small, dispersal-limited organisms at clearcut sites. In the buffer strips, the number of individuals decreased but not the number of species, indicating that buffer-strip retention is a good practice for protecting land snails in riparian forests. The varying effectiveness of the buffer strip could partly be explained by the proportion of the remaining basal area, emphasizing that buffer strips could be even more effective if efforts are made to avoid heavy damage by windthrows.     

Effects of Clear-Cut Harvesting on Boreal Ground-Beetle Assemblages (Coleoptera: Carabidae) in Western Canada

We compared pitfall catches from four types of mature lodgepole pine—white spruce forest with those from five age classes of young forest regenerating subsequent to clear-cutting. Ground beetles were most abundant in the youngest sites (1–2 years since cutting) and in the mature stands on moist soil. Species richness was higher in regenerating sites than in mature forest. Cluster analysis grouped the ground-beetle fauna according to forest age and forest type, suggesting that there is a general pattern of recovery after logging. Responses of common species to forest cutting fell into three groups: (1) forest generalists (2 species) were not dramatically affected, (2) species of open habitat (27 species) appeared and/or increased in abundance, and (3) mature forest species (10 species) disappeared or decreased in abundance. Populations of many mature forest species appear to recover following logging, but several specialists did not recolonize even the oldest regenerating stands. Furthermore, fragmentation and creation of large areas of relatively homogeneous young forest stages through logging may have detrimental long-term effects even on the more abundant forest generalists. We must better understand subtle variations in habitat in order to maintain invertebrate diversity while harvesting the boreal forest.     

Global effects of forest modification on herpetofauna communities

As the area covered by human-modified environments grows, it is increasingly important to understand the responses of communities to the novel habitats created, especially for sensitive and threatened taxa. We aimed to improve understanding of the major evolutionary and ecological processes that shape the assemblage of amphibian and reptile communities to forest modifications. To this end, we compiled a global data set of amphibian and reptile surveys in natural, disturbed (burned, logged), and transformed (monocultures, polyspecific plantations) forest communities to assess the richness, phylogenetic diversity, and composition of those communities, as well as the morphological disparity among taxa between natural and modified forest habitats. Forest transformations led to a diversity reduction of 15.46% relative to the statistically nonsignificant effect of disturbances. Transformations also led to a community composition that was 39.4% dissimilar to that on natural forests, compared with 16.1% difference in disturbances. Modifications did not affect the morphological disparity of communities (p = 0.167 and 0.744), and we found little evidence of taxon-specific responses to anthropic impacts. Monocultures and polyspecific plantations detrimentally affected the conservation and ecological value of both amphibian and reptile communities and altered the evolutionary processes shaping these communities, whereas forests with lower impact disturbances might, to some extent, serve as reservoirs of species. Although different mechanisms might buffer the collapse of herpetological communities, preserving remaining natural forests is necessary for conserving communities in the face of future anthropic pressures.     

Disturbance-Mediated Mammal Persistence and Abundance-Area Relationships in Amazonian Forest Fragments

Abstract:  Few researchers have investigated the synergistic effects of tropical forest fragmentation and disturbance on species persistence and abundance. We examined effects of both forest-patch metrics and forest disturbance in determining richness and abundance of midsized to large-bodied mammal species in a highly fragmented Amazonian forest landscape. Twenty-one forest fragments, ranging from 2 to 14,480 ha, and two continuous forest sites were sampled based on sightings, tracks, line-transect censuses, armadillo burrow censuses, and camera trapping. Patch occupancy of 37 species recorded ranged from 4% to all forest sites surveyed. Forest fragment size was the strongest predictor of species persistence, explaining 90% of the variation in species richness. Information-theoretic analysis confirmed that fragment area was the most important explanatory variable for the overall species richness and abundance of mammal species, followed by surface fires, which affected the abundance of seven species. Large mammal species were typically absent from fragments <100 ha, whereas some ubiquitous species were favored by fragmentation, exhibiting hyperabundance in small patches. Our findings highlight the importance of large (>10,000 ha), relatively undisturbed forest patches to maximize persistence and maintain baseline abundances of Neotropical forest mammal species.     

Amphibian Breeding Distribution in an Urbanized Landscape

Abstract:  Amphibians commonly use wetlands for breeding habitat, and given the concern about their ongoing global declines, the effects of urbanization on the breeding distribution of amphibians need to be quantified. Thus, we conducted a survey of the larval amphibian community in central Pennsylvania (U.S.A.) wetlands along an urbanization gradient. Wetlands in urban areas had less surrounding forest and wetlands and greater road density than rural wetlands. Urbanization was also associated with increases in hydroperiod (i.e., wetland permanency) and the presence of fish predators. Moreover, urban wetlands had lower larval amphibian species richness than rural wetlands. This decrease in richness was attributable to a decrease in occurrence of wood frogs ( Rana sylvatica ) and ambystomatid salamanders ( Ambystoma maculatum and A. jeffersonianum ) in urban sites. Wood frogs and ambystomatid salamanders were positively associated with the amount of forest surrounding sites and negatively associated with hydroperiod. As a result, we hypothesize that these species are sensitive to the effects of urban development. The remaining species in this study appear fairly resilient to the effects of urbanization. These data demonstrate the importance of quantifying both local and landscape attributes when describing the factors that limit the breeding distribution of amphibians. We recommend that to preserve amphibian biodiversity in urbanized landscapes, it is best to focus on regional diversity, which protects a variety of sites that encompass various hydroperiods, have adequate buffer habitat, and are connected by dispersal routes.