Center for Ecological Research

Effects of Forest Management on Amphibians

Along Headwater Streams

Eastern Newt (Notophthalmus viridescens - left) and Spring Salamander (Gyrinophilus porphyriticus - right), a species of Special Concern in Maine, are found along riparian streams in western Maine (below).

Riparian areas are one of the most complex, diverse, and dynamic environments in forested ecosystems.  In areas managed for timber, riparian areas are often protected with unharvested forested buffers, but it is unclear if these buffers are adequate to maintain the floral and faunal diversity of riparian areas. Amphibians are excellent candidates to study the effects of riparian timber management because they are sensitive to forest management, have high diversity in riparian areas, and are among the most abundant vertebrates in temperate forests.  We have been conducting several studies of amphibians along headwater streams in western Maine.

We conducted a field experiment with 15 headwater streams in western Maine randomly assigned to 5 silvicultural treatments.  We examined amphibian abundance for 1 year prior to and 2 years following treatment. We also undertook a retrospective study on 12 headwater streams representing 3 treatments where harvests had occurred 4-10 years earlier.  Pitfall traps with drift fences and cover-controlled, active-searches were used to sample terrestrial and stream amphibians. Wood frogs (Rana sylvatica), eastern red-backed salamanders (Plethodon cinereus), and spotted salamanders (Ambystoma maculatum) were sensitive to timber harvesting along headwater streams. American toads (Bufo americanus) were either unaffected or increased in abundance post-harvest. Buffers ranging in width from 11 to 35 m appeared to partially mitigate the effects of timber harvest, as abundances were generally higher within the buffer than in the adjacent clearcut for wood frogs, American toads, and to a lesser extent red-backed salamanders.  Partial harvests adjacent to headwater streams had the least effect on the riparian amphibian community and should be considered for harvests along headwater streams. Further analyses of these data are one going. The harvested streams are now 4 years post-harvest and we are looking for funding to add to this valuable data set.

Use of Amphibians to Define Riparian Zones of Headwater Streams

Riparian areas are known for high species richness and their influence on ecological processes. However, riparian zones are often difficult to define because they often have borders that are difficult to define, and because riparian zone definitions are shaped by the purpose of the definition (e.g., water quality or species protection). Defining riparian zones by examining habitat use of species that require both terrestrial and aquatic environments is one method that has not been thoroughly examined.  Headwater streams are important areas for amphibians in northeastern North America due to their combination of aquatic and terrestrial habitats and dominance throughout the landscape. In 2001 we sampled amphibians in western Maine with pitfall traps and drift fences that were adjacent to 15 first-order headwater streams.  Using traps located at five distances (1, 8, 18, 28, and 33 m) from the stream channel, we captured 1,897 amphibians of 10 species over 73,536 trap nights. We used a repeated measures analysis of variance to determine if species capture rates differed among pitfall trap locations and calculated Simpson’s and Shannon-Weaver diversity indices for the different trapping locations.  Six species were distributed uniformly from 0 to 33 m but a state-listed species, spring salamander (Gyrinophilus porphyriticus, Green 1827), and two additional stream species, two-lined salamander (Eurycea bislineata, Green 1818), and dusky salamander (Desmognathus fuscus, Green 1818) were captured in highest numbers in trap locations closest to the streams.  Total and average species richness was also highest in the trap location located closest to the stream. We conclude that the riparian zone as defined by amphibian species occurrence and abundance along headwater streams is relatively narrow (7-9 m), yet distinguishable due to high diversity and unique species occurrence.  The identification of a riparian zone for amphibians is the first step towards conservation. Manipulative experiments that involve different forest management practices should be conducted to determine what is necessary to conserve this unique area for amphibians.

Effects of Placing Sticks in Pitfall Traps on Amphibian and Small Mammal Capture Rates

Pitfall traps associated with drift fences are a common method of capturing amphibians to determine relative abundance, but they also capture and kill small mammals as non-target species. Pitfall traps have not been found to decrease amphibian populations, however they can decimate small mammal populations. We sampled 3 streams in 2000 and 8 streams in 2001. We sampled amphibians in pitfalls with and without escape sticks. Escape sticks were obtained at each study site and were between 0.6 and 1.5 cm in diameter. We did not detect any significant differences in capture rates between traps with sticks and traps without sticks for American toads (Bufo americanus), redback salamanders (Plethodon cinereus), or wood frogs (Rana sylvatica). We captured significantly more shrews, shorttail shrews (Blarina brevicauda), woodland jumping mice (Zapus insignis), mice, and Southern red-backed voles (Clethrionomys gapperi) in traps without sticks than traps with sticks placed in them. Capture rates of all small mammals combined were 14.5 times higher in pitfall traps without sticks than pitfall traps with sticks. Our results show the placement of sticks in pitfall traps can dramatically reduce the number of small mammal captures and subsequent mortalities without affecting amphibian capture rates.

For a more complete listing of the peer-reviewed articles that we have published on forestry and salamanders, please refer to our publications  - Dustin Perkins page.