Document: HOW-3-42-11

Grazing influences on species diversity and net primary production in a southern Appalachian wet meadow.

GEISSINGER, K.E.* and H.S.NEUFELD

Appalachian State University, Boone, NC, USA 28608 ¹

Abstract:
According to McNaughton's grazing optimization hypothesis, as grazing intensity increases, net primary productivity (NPP) should increase to an optimum, then decrease below that of ungrazed plants. This study was designed to test the hypothesis that grazing by cows affects NPP and maintains species diversity in mountain wetlands. In 1999 cattle were excluded from a portion of a wet meadow on the Blue Ridge Parkway. After one season of grazing exclusion, percentage representation by forbs, sedges and woody plant cover decreased in the grazed area, while in the ungrazed area, fern and sedge cover declined, but nonvascular and woody plant cover increased. Species richness did not change. Using periodic harvests, and grazing exclusion chambers on the grazed portion of the meadow, we estimated NPP at varying times during the season, and for most of the growing season. We also conducted a clipping study on the ungrazed side. Mean seasonal NPPs were 2.34 + 0.54 g m^-2 d^-1 in the grazed plots and 1.40 + 0.66 g m^-2 d^-1 in the ungrazed plots, while final standing crops were 153.8 + 24.4 g /m² and 323 + 82.3 g/m², respectively. NPP in a clipping treatment was 2.85 + 0.49 g m^-2 d^-1, not statistically different from the other treatments. However, if one outlier in the ungrazed side is removed, seasonal NPP of the ungrazed side drops significantly below that of the grazed side (0.77 + 0.23 g m^-2 d^-1. We also performed a greenhouse study of the response of two graminoids (Holcus lanatus, and Carex lurida - both are preferred browse) to artificial clipping and fertilization. A one time application of urea had no impact on unclipped Carex, but clipping reduced biomass by 38%. Fertilizing and clipping reduced biomass by 58%. Unclipped Holcus responded to fertilizing with a 46% increase in growth (92.3 + 4.1 g vs 63.3 + 3.2 g) while clipped plants produced only 31.0 + 1.7 g. These results suggest that elimination of grazing in these wet meadows may decrease NPP in the first year and alter cover of certain species groups, while severe grazing (greenhouse experiments) can be detrimental to overall productivity.

Keywords: Grazing, Blue Ridge Parkway, net primary productivity, species diversity

This abstract is being presented at: 3:30 PM in session:
HERBIVORE EFFECTS ON PLANTS