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A Large-Scale Experimental Approach to Determine the Effects of Coarse Woody Debris on the Species Richness and Relative Abundances of Amphibians and Reptiles on the Savannah River Site


Michael E. Dorcas

 

One of the most important components of proper management of forested lands is determining the habitat requirements of animals and how their habitat is affected by specific management practices. Harvesting and utilization of woody materials may significantly alter animals' habitats and thus impact species richness and relative abundances. Depending upon the intensity and frequency of thinning and factors affecting the mortality of trees, the amount of coarse woody debris (greater than 4-6 inches in diameter) at any given site will vary. Coarse woody debris (CWD) may have significant, and potentially beneficial, effects on populations of amphibians and reptiles inhabiting the area. The presence of CWD may provide important retreat sites with suitable thermal and hydric conditions for many species amphibians and reptiles. The presence of CWD may also provide an increased diversity and abundance of invertebrate and vertebrate prey for many species of amphibians and reptiles.

The USFS (Athens and Savannah River Forest Station) has established and will maintain four replicated experimental plots (approximately 15 ha each) on the Savannah River Site (SRS) during the Summer of 1996 in which CWD is controlled in specific ways to facilitate integrated research to determine the potential role of CWD as a key resource. The following treatments have been agreed upon after considerable consultation between researchers at SREL, SRFS, UGA, Clemson University, and the USFS (Athens):

  1. A control in which CWD is not manipulated.
  2. Removal, in which all of the woody debris (anything greater than 4 inches in diameter) is removed, including standing snags. This treatment will be maintained for three years, after which, it will be available to be used as an augmentation treatment.
  3. Removal, in which all of the woody debris is removed, except for standing snags.
  4. A control as described in treatment number one for a baseline period (3 years), then extensive felling to simulate a catastrophic wind-fall that would result in a large pulse of CWD.

The SRFS has established four replicates of the four treatments in similar stands (loblolly pine) on the SRS. Each set of replicates is at least 200 meters from any wetland or primary road. The SRFS will maintain all treatments with some restrictions to allow thinning and burning operations at preplanned intervals. However, all management operations will be conducted at the same time on all plots so that all plots experience similar levels of disturbance at the same times.

The overall goal of the research described here is to determine the effects of CWD on the species richness and relative abundances of amphibians and reptiles on the SRS. The results of this research will be of benefit to the USDA Forest Service, SRS Forest Service, the Forest Service in Athens, and the commercial wood products industry by increasing our knowledge of how amphibians and reptiles respond to CWD. The results of these studies should be very important when considering the effects of CWD during the development of management plans for forested lands.

Our approach is to use drift fences with pitfall and funnel traps to determine the species richness and relative abundances of amphibians and reptiles. We have constructed four drift fences (each 30 meters long) with pitfall traps and funnel traps to sample amphibians and reptiles in all of the control and removal plots (treatments 1 and 3 above). Each drift fence has one pitfall trap at each end and a pair of pitfall traps, one on either side, in the center of the fence. Two pairs of funnel traps, one on each side, are positioned at 10 meter intervals along the drift fence. The pitfall traps are used to capture salamanders, anurans, lizards, and small snakes. The funnel traps are used to capture larger snakes, lizards, anurans, and salamanders. The drift fences are set out in perpendicular arrays in the center of each treatment plot to capture animals moving in all directions. We sample every day on alternate weeks (i.e., one week on, one week off). When captured, amphibians and reptiles will be identified, counted, and marked (either toe-clipped or pit-tagged) to allow us to determine species richness and relative abundances.

In addition to providing important basic information on how the structural environment affects populations of amphibians and reptiles, the results from the above research will be of benefit to the USDA Forest Service, SRS Forest Service, the Forest Service in Athens, and the commercial wood products industry by increasing our knowledge of how amphibians and reptiles respond to CWD. The results of these studies should be vital when considering the effects of CWD during the development of management plans for forested lands.

 
 
 
 
 
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