Table of Contents Executive Summary 2



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Methods


  • Research: We conducted an extensive literature review to determine the context, extent, and factors related to amphibian mortality with roads and other causes. Through email we communicated with people in Transportation Industry such as Nelson Hoffman, Chris Slesar, and Chad Allen from VTRANS. Information was also gathered via email with people in Construction Agencies such as Robert Flint of the Florida Department of Transportation to determine costs of various efforts. Email with biologists such as Scott Jackson from University of Massachusetts was used to gather information on amphibian requirements for culverts.

  • Site Assessment: We designed a site assessment metric to prioritize sites based on several parameters. GIS data layers containing these parameters were downloaded Vermont Center for Geographic Information (VCGI); we utilized all of the applicable data currently available in digital format for Grand Isle and Franklin Counties. The metric was developed to include all culverts found within 400 meters of wetlands. This distance was chosen due to it being the approximate maximum distance traveled by amphibians that migrate to and from wetland habitats. Within these culverts we then prioritized sites based on traffic volume, viable upland habitat, and proximity to ideal amphibian habitat (wetlands). A traffic volume of 6000 vehicles per day was selected to represent an estimated mortality rate of >90% for amphibians crossing the road (Hels and Buchwald 2001). We then narrowed the ranges on the existing parameters to identify high priority sites. The high priority sites were chosen based on the presence of wetland habitat within 100 meters of a culvert (this includes the maximum distance traveled between habitats for almost all Vermont amphibians), and a road with a traffic volume > 6000 vehicles per day. A detailed GIS map of all high-priority sites was created including all data relevant to the metric.

  • Recommendations: The recommendations were compiled through analysis and interpretation of the findings and from the results of the metric. Based on the parameters needed for a detailed statewide site assessment metric we also compiled a list of missing information.



Research


The following section of this report will include all of our research findings utilized in creating recommendations for future management actions. An extensive literature review was conducted to find both the factors and causes behind the problem as well as potential management alternatives. Vehicle encounters are a significant source of mortality for certain amphibian species due to movement patters and the increasing presence of roads and vehicles near and through amphibian habitat. The need to reduce this source of mortality is greatly strengthened by global population declines evident in amphibian populations across the planet. These population declines are thought to be the result of anthropogenic degradation of the global environment. This section of the report will also present the research findings that formed the basis for our management recommendations for future actions of the Vermont Agency of Transportation.

Habitat Destruction, Alteration, and Fragmentation


Most amphibians require both terrestrial and aquatic habitats to complete their life cycles, which makes them even more vulnerable to habitat loss, alteration, and fragmentation than most other wildlife species. Loss of either habitat may have negative impacts on amphibian populations, yet both have been greatly modified by anthropogenic disturbances. Some of the major land-use practices affecting amphibians include agriculture, silviculture, industry, and urban development. These practices often lead to the filling and draining of aquatic breeding habitat (especially wetlands and vernal pools), the removal of trees and other vegetation in the terrestrial uplands used by adults for feeding and refuge, and the alteration of the hydrodynamics associated with stream and river ecosystems (Semlitsch 2003a).

Habitat destruction and habitat alteration are two distinct processes, but both have detrimental effects on amphibian populations. Additionally, they both contribute to habitat fragmentation, out of which arises a host of additional problems. Habitat destruction is the complete, and often permanent, loss of an ecosystem and its former biological function. This occurs when wetlands are drained or filled; forests are converted to parking lots, housing developments, agricultural fields, etc.; or when an ecosystem becomes so chemically contaminated that it is uninhabitable. On the other hand, habitat alteration occurs when an ecosystem function is changed, although not completely or permanently. An example of habitat alteration is when trees are cut in a forest as part of a forestry operation. Removal of the canopy will have an effect on the microhabitat and microclimate of the forest, perhaps reducing or eliminating amphibians, but the trees will grow back and suitable habitat will once again exist. The effects of habitat destruction and alteration become most pronounced when they occur on a sufficient scale that habitat fragmentation occurs (Dodd and Smith 2003).

As many amphibian populations exhibit metapopulation structure, fragmentation of both aquatic and terrestrial habitats may lead to numerous issues. As the number of suitable breeding sites decreases, the total number of individuals available to recolonize extirpated populations or form new populations is diminished. This may lead to a reduction in the number of source populations as well. The loss of aquatic habitat may also lead to isolation of populations and the subsequent loss of genetic diversity, as they may be too far apart to allow successful dispersal. Even more important than aquatic breeding sites may be intact terrestrial habitat, because this provides movement corridors that connect local populations. Because amphibians are prone to desiccation, they require moist microclimates provided by intact canopy cover, coarse woody debris, and leaf litter to successfully migrate between habitats. Barriers introduced by fragmentation, such as housing developments, roads, and agricultural fields, may restrict movement (Semlitsch 2003b).

The immediate effects of fragmentation on amphibian populations include the loss of the most vulnerable individuals, populations, and species. As the landscape becomes increasingly fragmented, the natural linkages between habitat patches are lost and barriers to movement are introduced. At this point, they may become isolated from habitats required to complete their life cycles, such as if aquatic breeding sites are cut off from terrestrial sites. There may be an increased risk of predation as edge effects are introduced and cover is reduced. Fragmentation may remain a filter to movement or may become an impenetrable barrier (Dodd and Smith 2003).

Long-term effects of fragmentation include the loss of genetic variability, decreased survivorship, isolation, increased edge effects, and greater susceptibility to stochastic events. Small, isolated populations confined to the tiny pieces of remaining habitat become susceptible to the accumulation of mutations and the loss of adaptive potential. Edge effects become more pronounced and may alter the physical structure and microclimate of the habitat. There is often the loss of migratory routes and dispersal corridors, compounding the problems of isolation. These long-term pressures on the populations, combined with loss of individuals to direct mortality, can become too much for the populations to overcome. They become more vulnerable to extirpation, and possibly extinction, due to random stochastic events, such as disease, drought, etc. (Dodd and Smith 2003).


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