Collaborative Research: Land-Use Practices And Persistence Of Amphibian Populations

Over the past 200 years, conversion of land for agricultural use, industrial development, and urban sprawl has drastically reduced natural habitat for many species and is considered the most serious threat to biological diversity. Fragmentation divides once continuous natural habitats into smaller pieces that are often separated by areas unsuitable to sustain viable populations. The goal of the proposed research is to understand how important local population and metapopulation processes are altered by fragmentation of natural habitats in a model system of pond-breeding amphibians. The primary objectives of the proposed study are to experimentally compare demographic and behavioral responses of amphibians in clear-cut (with and without coarse woody debris), partial-cut, edge, and intact forest habitats around replicated natural breeding ponds. These results will lead to a better understanding of the habitat requirements for successful recruitment and survival of local populations, and how amphibians disperse through fragmented landscapes. It will allow strong inferences about the disruption of metapopulation dynamics in amphibians caused by fragmentation and about how to prevent population declines and extinctions. Further, information from this project is essential to the development of conservation and management plans in state natural resource agencies, the U.S.D.A. Forest Service, and the Bureau of Land Management

Collaborative Research: Land-Use Practices And Persistence Of Amphibian Populations.

Over the past 200 years, conversion of land for agricultural use, industrial development, and urban sprawl has drastically reduced natural habitat for many species and is considered the most serious threat to biological diversity. Fragmentation divides once continuous natural habitats into smaller pieces that are often separated by areas unsuitable to sustain viable populations. The goal of the proposed research is to understand how important local population and metapopulation processes are altered by fragmentation of natural habitats in a model system of pond-breeding amphibians. The primary objectives of the proposed study are to experimentally compare demographic and behavioral responses of amphibians in clear-cut (with and without coarse woody debris), partial-cut, edge, and intact forest habitats around replicated natural breeding ponds. These results will lead to a better understanding of the habitat requirements for successful recruitment and survival of local populations, and how amphibians disperse through fragmented landscapes. It will allow strong inferences about the disruption of metapopulation dynamics in amphibians caused by fragmentation and about how to prevent population declines and extinctions. Further, information from this project is essential to the development of conservation and management plans in state natural resource agencies, the U.S.D.A. Forest Service, and the Bureau of Land Management

Predation by Amphibians and Small Mammals on the Spruce Budworm (Lepidoptera: Tortricidae)

Stomach-content analyses of pitfall-trapped amphibians and small mammals showed that the eastern American toad, Bujo americanus americanus, and the wood frog, Rana sylvatica, preyed on late instars and moths of the spruce budworm, Choristoneura fumiferana. The spotted salamander, Ambystoma maculatum, and the masked shrew, Sorex cinereus, also preyed on late instars of the spruce budworm

Clearcutting has a long-lasting effect on habitat connectivity for a forest amphibian by decreasing permeability to juvenile movements

Conservation of forest amphibians is dependent on finding the right balance between management for timber production and meeting species\u27 habitat requirements. For many pond-breeding amphibians, successful dispersal of the juvenile stage is essential for long-term population persistence. We investigated the influence of timber-harvesting practices on the movements of juvenile wood frogs (Lithobates sylvaticus). We used a chronosequence of stands produced by clear-cutting to evaluate how stand age affects habitat permeability to movements. We conducted experimental releases of juveniles in 2008 (n = 350) and 2009 (n = 528) in unidirectional runways in four treatments: mature forest, recent clearcut, 11-year-old, and 20-year-old regeneration. The runways were 50 x 2.5-m enclosures extending into each treatment, perpendicular to a distinct edge, with four tracking stations at 10, 20, 30, and 40 m from the edge. We recorded the number of animals reaching each tracking station, and the proportion of animals changing their direction of movement at each distance. We found that the mature forest was 3.1 and 3.7 times more permeable than the 11-year-old regeneration and the recent clearcut, respectively. Animals actively avoided open-canopy habitats and sharp edges; significantly more animals returned toward the closed-canopy forest at 0 m and 10 m in the less permeable treatments. There were no significant differences in habitat permeability between the mature forest and the 20-year-old regeneration. Our study is the first to directly assess habitat permeability to juvenile amphibian movement in relation to various forestry practices. We argue that habitat permeability at this scale is largely driven by the behavior of animals in relation to habitat disturbance and that caution needs to be used when using spatial modeling and expert-derived permeability values to assess connectivity of amphibian populations. The effects of clear-cutting on the migratory success of juvenile L. sylvaticus are long-lasting. Forestry practices that involve canopy removal and conversion of natural forest to conifer plantations may affect regional population viability by hindering successful dispersal

Initial Movements of a Dispersing Amphbian in Response to Partial Harvestion in the Acadian Forest of Maine, USA

Maintaining amphibian populations in managed forests requires a balance between timber extraction and retaining functional connectivity for animals that use multiple vegetation types to satisfy habitat requirements, particularly where extensive harvesting may increase fragmentation. Quantifying dispersal patterns in response to harvest, especially across high-contrast edges adjacent to unlogged forest, is critical for evaluating the effects of harvest configuration on amphibians. We tested the initial post-metamorphic orientation of juvenile wood frogs (Lithobates sylvaticus) at edges in harvests (31– 60% retention standwide) in the Acadian forest of Maine, USA, during the period when juveniles emigrate from breeding pools. We released juveniles (n = 621) in 10-m diameter arena enclosures spanning edges. Frog movement in uncut controls (~70 –75% canopy) was contrasted with movement in the following: harvester trails (0% retention) running parallel to edges of uncut forest; perpendicular harvester trails; or residual strips of partially cut matrix-forest (~30% retention) between trails. We observed a nonsignificant trend for higher proportions of individuals entering control forests versus harvests (x12 = 2.504, P = 0.113) and a stronger trend for movements into control forests versus perpendicular-oriented trails (52:35 for forest versus treatment; x12 = 3.322, P = 0.068). The biological relevance of such patterns warrants further consideration. Juveniles may enter partial harvests at rates similar to those for intact forest, but quantifying the effects of harvest configuration on movement patterns, residency times, and ultimately survival is necessary to determine whether these harvests represent sink habitats

Movement in the matrix: Substrates and distance to forest edge affect postmetamorphic movements of a forest amphibian

Population persistence often depends on functional connectivity for animals that transit multiple vegetation types to acquire resources, particularly for dispersers navigating a landscape matrix fragmented by agriculture, forestry, or urbanization. For many pool-breeding amphibians, population viability depends on the ability of juveniles to locate and reach suitable habitat in the terrestrial matrix. Thus, identifying the scale and orientation of movements is necessary to predict the consequences of landscape configuration for populations. We conducted three experiments to evaluate if different vegetation types alter the behavior of post-metamorphic wood frogs (Lithobates sylvaticus). We measured the: (1) fine-scale movement (velocity, latency, path length, net displacement, path tortuosity, and orientation) of individuals (n = 150) released on five substrates (asphalt, corn, forest leaf litter, hay, lawn); (2) directionality of frogs (n = 168) released at different distances from forest in two open-cover types (lawns, hayfields); and (3) willingness of frogs (n = 240) to enter three land-cover types (asphalt, lawn, forest) when released within artificial refugia islands at different distances from forest. Using fluorescent powder, we mapped 318 movement paths and performance differed. Frogs demonstrated straighter paths, and greater net movements, path lengths, and velocities through treatments with lower structural complexity (asphalt \u3e lawn \u3e corn \u3e forest leaf litter \u3e hay). Frogs also exhibited forest-oriented directionality in asphalt, lawn, and corn but random orientation in forest control and hay. The willingness of individuals to leave a refugia island was lowest on asphalt (12% of released frogs), moderate on lawn (40%), and very high in forest (90%). Overall, results indicate that the quality of nonforest matrix may influence the ability of frogs to traverse open cover and orient toward forest from distances of ≥40–55 m. Thus, it is inaccurate to assume movement performance is uniform across all open-matrix types, an important distinction because many landscape-population models use expert-based values that are a one-size- fits- all measure for open cover. Our study provides field-based, mechanistic approximations of juvenile movement that can be useful for predicting how matrix composition and configuration might be managed to maintain or restore functional connectivity

Different open-canopy vegetation types affect matrix permeability for a dispersing forest amphibian

Population viability often depends on conserving functional connectivity in fragmented landscapes. For pool-breeding amphibians, population connectivity is largely maintained through juvenile dispersal, often through various vegetation types that may differ as filters or conduits to movement. We quantified the relative permeability of different types of open-canopy vegetation to juvenile wood frogs Lithobates sylvaticus to determine whether this influences functional connectivity during dispersal. We conducted experimental releases of juveniles (n = 561) in ten runways representing five treatments: hayfield, moderate-cover lawn (45–85% cover), open lawn (0% cover), row crop (forage-corn) and recent clear-cut. Runways consisted of 35 × 2·5 m enclosures, located perpendicular to a forest edge and extending into treatment areas with tracking stations at 10, 20 and 30 m. As indices of permeability, we measured the number of animals traversing each station, the proportion changing direction, movement timing and movement rates. Based on an index that compounds four metrics and scales them relative to mature forest as a control, permeability varied between open-canopy cover types in the following order: row crop \u3c hayfield \u3c clear-cut \u3c open lawn \u3c moderate-cover lawn. The highest proportions of individuals changed direction (towards forest) in the hayfield, moderate-cover lawn and clear-cut, suggesting that juveniles may make forays into the open and subsequently assess habitat. Nonetheless, individuals could eventually transit entire runways, indicated by overall recaptures at 30 m (e.g. hayfield, 29%; moderate-cover lawn, 24%; and clear-cut, 20%) at the end of our six-week experiment. Synthesis and applications. We provide quantitative evidence that open-canopy cover types may act as differential ecological filters to ranging movements, and ultimately dispersal. Differences in the willingness of animals to enter treatments, coupled with motility and residency times, support the differing roles of open-canopy vegetation as both filters and conduits to movement. Thus, it may be overly simplistic to estimate matrix permeability as uniformly low in models that predict movement in fragmented landscapes. To promote functional connectivity, modification of vegetation composition and configuration may provide an underutilized tool for conservation practitioners to reduce the effective isolation of habitat patches for post-metamorphic amphibians

MP716: New Forestry in Eastern Spruce-Fir Forests: Principles and Applications to Maine

Eastern North America\u27s spruce-fir forests have a unique ecological and human history which is reflected in their current vegetation, ownership patterns, and forest management practices. Furthermore, there are important differences within the region between the true boreal forest and the sub-boreal Acadian forest; this paper emphasizes the Acadian forest. Applying New Forestry to this region will require a modified approach which we outline by describing three basic principles. First, to provide the landscape context for New Forestry, we propose a triad of forest land allocation in which reserves and plantations would co-exist, surrounded by and embedded within a landscape managed by alternative silvicultural systems based on New Forestry principles. The second principle is that silvicultural systems should be patterned after local natural disturbance regimes. The third principle is that ecosystems that have been altered by past practices should be restored. Implementing these principles is discussed in a review of specific silvicultural practices: conservation and restoration of seed sources; retention of residual trees; long rotations; limited whole-tree harvesting; and two-aged stands maintained by irregular shelterwood cutting. At the landscape level we discuss how the triad might be implemented and the importance of size and distribution of harvest areas and riparian zones.https://digitalcommons.library.umaine.edu/aes_miscpubs/1027/thumbnail.jp

Comparing relative abundance of amphibians in forest canopy gaps of natural origin vs. timber harvest origin

Relative abundance of amphibians in forest canopy gaps of natural origin vs. timber harvest origin.— Small–scale canopy gaps created by logging may retain adequate habitat structure to maintain amphibian abundance. We used pitfalls with drift fences to measure relative abundance of amphibians in 44 harvested gaps, 19 natural treefall gaps, and 36 closed–canopy forest plots. Metamorphs had relatively lower capture rates in large harvest gaps for Ambystoma maculatum, Lithobates catesbeianus, L. clamitans, and L. sylvaticus but we did not detect statistically significant (p \u3c 0.1) differences among gap types for Lithobates palustris metamorphs. L. clamitans juveniles and L. sylvaticus juveniles and adults had relatively lower capture rates in large harvest gaps. For juvenile–adult A. maculatum, we caught relatively fewer individuals in all gap types than in closed–canopy areas. Some groups with overall lower capture rates (immature Plethodon cinereus, juvenile L. palustris) had mixed differences among gap types, and Notophthalmus viridescens (efts) and adult P. cinereus showed no differences among gap types. One species, L. clamitans, was captured more often at gap edges than gap centers. These results suggest that harvest gaps, especially small gaps, provided habitat similar to natural gaps for some, but not all, amphibian species or life–stages

Potential Effects of Insecticides on the Survival of Dabbling Duck Broods

The effect of insecticides on the survival of dabbling duck broods was investigated by reviewing studies of natural brood survival and depression of growth rates for ducklings raised on wetlands treated with insecticides. Ducklings raised on an insecticide-treated wetland took 5 days longer to reach the normal 14-day body weight. Normal brood mortality for three species of dabbling ducks was highest in the first two weeks of life and ranged from 25% to 51%. High mortality of young ducklings is probably related to their small size. Thus, mortality rates could be in creased to 35% to 70% because of the delay in growth. Other potential effects of invertebrate reductions on breeding dabbling ducks are discussed and suggestions for future research are provided