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Oak Loss and Spiders

by Louise Lynch

Winter 2011

Plant life is the bridge between the sun and organic energy, dictating the biodiversity of a habitat. Oak-dominated forests are a common habitat throughout the eastern United States, so many of our forest communities and their ecology are built on the dominance of oak species.  However, factors including climate change, soil change, native and exotic diseases, and increasing deer populations are changing the composition of our forests. These changes, in turn, will likely cause changes in the diversity of forest invertebrate communities. Since May 2010, I have assisted Dr. Vladimir Ovtsharenko of the American Museum of Natural History in studying the invertebrate community of Black Rock Forest for the Future of Oak Forestsproject.

The study area consists of twenty 1.3-acre plots that have been treated to vary canopy tree composition.  Project plots include controls (canopy composition untouched), plots with all oaks removed, plots with half of the oaks removed, and plots with all non-oak species removed  Each plot also includes an area fenced to exclude deer and other large mammals.

While the invertebrate study includes the community as a whole, spiders are of special interest. As predators, spiders depend on the composition and quantity of prey organisms.  Changes in their numbers and biodiversity would follow alterations in their prey, which in turn would follow changes in the prey’s food sources and habitats caused by canopy changes.

I collected and combined three pitfall traps from each plot every 7 to 10 days.  I sorted, counted, and identified all specimens to the level of class.  Spider specimens will eventually be identified to the level of species. By comparing data collected in the treated plots to data from the control plots, it is possible to analyze the effect of changes in canopy composition on invertebrate populations.

Preliminary data show that the total mass of spiders more than doubled in the 100% oak-girdled plots and that abundance also increased, compared to the control plot. Additionally, a rapid decline in oak dominance has a greater effect in increasing spider biomass and abundance than a decline of non-oak species.

Louise Lynch is studying for a Masters of Science in entomology at the University of Nebraska-Lincoln. She worked with Dr. Vladimir Ovtsharenko of the American Museum of Natural History on the spider study portion of the Oak Forest Project.