Monday, November 29, 2010

Changing Vegetation & the Herpetofauna

Sceloporus undulatus
Managing forests (logging, reforestation, clearing brush, using herbicides, etc) can have unforeseen consequences for wildlife. As vegetation goes through succession it creates a variety of changing micro-environments that favor some species over others, so as the stages of succession change the animal populations change with them. This concept has been long known and its application to rattlesnakes was noted in Philip Tome’s 1845 book, Thirty Years a Hunter. Tome lived in northeastern Pennsylvania and described frequent encounters with Timber Rattlesnakes (Crotalus horridus).  Tome described the early setters burning forests to control rattlesnakes. Of course, in the long term this opened up the canopy and provided more basking sites. Jäggi and Baur (1999) linked the decline of Viper aspis populations to changes in vegetations, and other authors have made similar reports of changes in snake populations to changes in vegetation.

Kevin Shoemaker and James Gibbs of the State University of New York now report that the Eastern Massasauga (Sistrurus c. catenatus) persists as two isolated populations at the eastern edge of the species’ geographic range, and those two populations are threatened by the increasing density of woody plants. They found microhabitat temperatures were substantially lower at the closed-canopy site, where catenatus selected the warmest available basking sites.
At an open-canopy catenatus selected basking sites that afforded greater cryptic cover. And, they recommend the experimental reduction of shrub cover to improve basking habitat at the closed-canopy site. But they caution that management efforts to reduce shrub cover for basking should maintain adequate cryptic cover, (that is the grasses, leaf litter, rocks, and other cover) used by the snakes to conceal themselves.

In another paper, Charlotte Matthews and colleagues (2010) report that the recent use of prescribed fire and fire surrogates to reduce fuel hazards has spurred interest in their effects on wildlife. They conducted studies to determine the impact of “reducing fuel” in forests on amphibian and reptile populations in areas that were twice burned, had the understory cut mechanically, and in an area that had the understory cut mechanically followed by two burns. They trapped the herpetofauna using pitfall and funnel traps. The study was done at the Green River Game Land, Polk County, North Carolina. The results revealed that salamanders were reduced in number in the twice burned, mechanically opened habitats – possibly because this site had reduced leaf litter.  While these same habitats supported larger numbers of lizards and snakes, undoubtedly due to the increased number of basking sites and the newly created thermal gradients.

Jaggi, C., and B. Baur. 1999. Overgrowing forest as a possible cause for the local extinction of Vipera aspis in the northern Swiss Jura mountains. Amphibia-Reptilia 20:25–34.

Matthews, C. E., C. E. Moorman, C. H. Greenberg, and T. A. Waldrop. 2010. Response of Reptiles and Amphibians to Repeated Fuel Reduction Treatments. Journal of Wildlife Management 74(6):1301-1310.

Shoemaker, K. T. and J. P. Gibbs. 2010. Evaluating basking-habitat deficiency in the threatened Eastern Massasauga Rattlesnake. Journal of Wildlife Management 74(3):504-513.

Tome, P. 1854. (1989 reprint) Pioneer Life; or, Thirty Years a Hunter. Baltimore: Gateway Press.

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