Clearcutting Effects

Up
Experiment

Ambystoma opacum: photo, David Scott

One of the most challenging tasks currently faced by forest resource managers is the growing need to accommodate multiple demands including preserving biodiversity, and protecting nutrient cycling and water quality, all while maximizing forest productivity (Harris 1984, Petranka et al. 1994). Increasing awareness of conservation and legislation, such as the 1973 Endangered Specie Act and the 1976 National Forest Management Act, now effectively require resource managers to maintain viable populations of plants and animals and make preservation of biodiversity central components of long-term management strategies.  In general, resource managers have responded to requirements to preserve biodiversity by focusing their attention on the management of single species perceived to be at greatest risk (e.g., "endangered" or "threatened"). However, it is becoming increasingly clear that managing for a single species may have unintended consequences for species not explicitly considered in management plans (e.g., Liu et al. 1995). In order to successfully preserve overall biodiversity and avoid threatening one or several species as a result of management for a focal species, management plans will need to account for differences among taxa by assessing the effects of particular management strategies.

Attempts to develop comprehensive forest management plans are currently limited by both an uncertainty aout which taxa should be explicitly considered, as well as a lack of information about the actual effects of specific forest management practices on identified taxa (Beiswenger 1988). Forest-dwelling amphibians are a compelling example of both shortcomings. For instance, amphibians have been recognized as an important component of ecological communities (Burton and Likens 1975, Pogh et al. 1987, Heyer et al. 1994), nevertheless, data on amphibian responses to habitat changes are limited (Harlow and Van Lear 1987). Consequently, amphibians are often overlooked in management decisions concerning biodiversity (Grant et al. 1994, Petranka et al. 1993).

In the Southeastern U.S., many amphibian species utilize temporary, isolated freshwater wetlands and the surrounding terrestrial habitat (Gibbons and Semlitsch 1991). Persistence and maintenance of populations in these areas may depend on the exchange of animals among ponds and successful breeding at a new location (Gill 1978, Reading et al. 1991, Sinsch 1992); however, forest management practices may effectively isolate populations by leaving little unaltered woodland around a wetland. In recent years, there have been an increasing number of studies on population responses of amphibians to habitat changes. Most studies have compared population sizes and species richness between logged and undisturbed (or older) habitat (e.g. Bennett and Gibbons 1980, Enge and Marion 1986, Pough et al. 1987, Ash 1988, Welsch and Lind 1988, Dodd 1991, Raymond and Hardy 1991, Petranka et al. 1993, Grant et al. 1994, Petranka et al. 1994). Taken together, comparative data suggest that both amphibian population size and species richness are lower in disturbed habitat than in undisturbed habitat. However, conclusions about the effects of clearcutting on amphibians are ultimately limited by the absence of spatial and temporal controls in comparative studies. Complementary evidence from experiments that directly demonstrate the effect of specific silvicultural practices on amphibian populations is entirely lacking.

Anne C. Chazal and I used an experimental approach to measure some of the effects of clear-cutting on survival, growth, body condition and reproduction of one year-old mole salamanders, Ambystoma talpoideum. We focused on the effects clearcutting has on the life history traits of individual salamanders because variation in individual life history traits has direct consequences for population demography and dynamics (Dunham et al. 1991). For example, body size is positively correlated to clutch size in female A. opacum (Scott 1994) and A. talpoideum (Semlitsch 1987). Furthermore, body size at metamorphosis affects the age at first reproduction with larger individuals returning to the breeding site at an earlier age (Scott 1994). Our experiment is a specific test of the general hypothesis, suggested by comparative data, that clearcutting negatively impacts life history traits of forest dwelling salamanders.