Author
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Tracy, Benjamin |
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Sanderson, Matt |
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Submitted to: Journal of Plant Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/9/2000 Publication Date: 7/20/2000 Citation: Tracy, B.F., Sanderson, M.A. 2000. Patterns of plant species richness in pasture lands of the Northeast United States. Plant Ecology. 149:169-180. Interpretive Summary: Little information exists about plant species diversity and composition of northeast (NE) pastures. Given this lack of information, we designed a broad vegetation survey to answer some fundamental questions about species diversity. This information could be useful for designing future management strategies to manipulate plant species mixtures for pasture improvement. A total of 17 farms, encompassing 37 pastures, were sampled in six NE states during July and August, 1998. We positively identified 161 different plant species across the study region. White clover, dandelion, broadleaf plantain, English plantain, bluegrass, red clover, orchardgrass, and tall fescue were some of the most common species in our sampling area. Pastures averaged 32 species over 0.2 acre. Most of these species (~90%) were transient weedy species that accounted for little overall ground cover in pastures. Perennial broadleaf species were the most diverse functional group, averaging 12 species per pasture, while perennial grasses and legumes averaged 7 and 4 species, respectively. The number of species in NE pastures was comparable to other grasslands in the U.S. We found the diversity of pastures neither increases nor decreases over time because grazing arrests normal succession to more diverse woodlands, otherwise, land management and environmental variables were generally poor predictors of plant species diversity. We found that weedy pastures were associated with low phosphorus soils. The occurrence of weedy species that make up most of the plant diversity in pastures seems to be dependent on the diversity of weed seeds in soil and random pasture disturbances by cattle. These disturbances by cattle create gaps in pasture and allow various kinds of transient weed species to establish. Technical Abstract: Pasture lands are an important facet of land use in the northeast (NE) United States (U.S.), yet little is known about their diversity. Pasture lands may become even more important in the NE as farmers increasingly convert crop land to perennial grazing pasture as an alternative way to supply forage to livestock. Because little information exists about the ecology of NE pastures, we designed a vegetation survey to answer some fundamental questions about their species diversity. Our objectives were to document plant richness across a broad spectrum of NE pastures using an intensive, multi-scale sampling method and compare the richness of NE pasture lands with: 1) grazed grasslands in the western U.S., and 2) abandoned agricultural lands in the eastern U.S. that had not been grazed. We also wanted to learn whether environmental (soils or climate) or land management variables could help explain patterns of richness. A total of 17 farms, encompassing 37 pastures, were sampled in New York, Pennsylvania Vermont, Maryland, Massachusetts, and Connecticut during July and August, 1998. We positively identified a total of 161 different plant species across the study region. Species richness averaged 31.7 +/- 1.1 on pastures and was similar to grazed grasslands in the western U.S. at both 1 m2 and 1000 m2 scales. Infrequent, transient species that were mostly perennial and annual forbs accounted for ~90% of the species richness. Environmental variables (soils and climate) and land management histories were generally poor predictors of plant richness at large spatial scales. At the 1000 m2 scale patterns of species richness are best explained by the species diversity of soil seed banks or seed rain, and stochastic recruitment of these species into existing vegetation. |
