PARENT SESSION
Oral Session #1: Invasive Species Control.
Presiding: S. Smith
Monday, August 5. 8:00 AM to 11:30 AM. Mohave Meeting Room, TCC.
Impact of chemical control of native invasive plants on understory diversity in northern hardwood forests.
Ristau, Todd*,1, Horsley, Stephen1, 1 USDA Forest Service, Irvine, PA
ABSTRACT- White-tailed deer have intensively browsed Pennsylvania's forests for 70 years, effectively eliminating the natural shrub layer. Dense understories of Acer pennsylvanicum, Fagus grandifolia, Dennstaedtia punctilobula and Thelypteris noveboracensis become invasive without competition. Herbicide, often with fencing and partial cutting, is an effective method for reducing competition with tree species establishment. Beginning in 1994, we tested the effects of glyphosate plus sulfometuron methyl herbicides on understory diversity at 10 partially cut 8 ha sites on the Allegheny National Forest. Half of each received herbicide and half remained untreated. At each site, richness searches and abundance assessments using 30 4-m2 quadrats were conducted biannually through 2000. No species was consistently eliminated by herbicide across sites. Abundance of all species was initially reduced. Targeted species remained less abundant on treated vs. control plots after 6 years. Grasses and sedges had higher abundance on treated plots after 4 years. One species, Oxalis acetosella, had significantly lower abundance after 6 years. Dominance, evenness and the Shannon diversity index were not different among treatments before or at any time after treatment. Pre-treatment richness was not different; however immediately after herbicide there were 5 fewer species on average in treated plots. The difference was gone after 4 years, and after 6 years, treated plots had one more species than controls. Results suggest that chemical control of native invasives does not permanently reduce understory plant diversity.
KEY WORDS: understory diversity, herbicide, Dennstaedtia punctilobula, Thelypteris noveboracensis