Sampling to assess species diversity of herbaceous layer vegetation in Allegheny hardwood forests

RISTAU, T. E. AND S. B. HORSLEY (USDA Forest Service, Forestry Sciences Lab oratory, PO Pox 767, Irvine, PA 16329) and L. H. Me CORMICK (School OF Fore st Resources, The Pennsylvania State University, University Park, PA 16802) . Sampling to assess species diversity of herbaceous layer vegetation in Al legheny hardwood forests. J. Torrey Pot. Sec. 128:000-000. 2001. - The opti mum frequency and time of sampling required to generate comprehensive diver sity indices of herbaceous species in Allegheny hardwood forests was studie d. Four 8-ha sites on the Allegheny National Forest were sampled monthly fr om May to August in 1992 and 1993 for herbaceous layer species composition and percent cover. Each site included GO circular 4-m(2) plots, Fifteen tal ly combinations created by combining sample times (1, 2, 3 and 4 at a time) were used to generate: diversity indices. Herbaceous species in Allegheny hardwood forests were categorized as common or infrequent. Common plants we re present throughout the growing season and their abundance remained stabl e. Infrequent plants differed in abundance and presence throughout the stud y. Coverage of several plants increased from May to July as they became ful ly developed. Species richness increased with number of sample times. Tile Shannon Diversity index and the Shannon Evenness index did not show differe nces attributable to time of sampling. Sampling for herbaceous species dive rsity in Allegheny hardwood forests should include two inventories, one ear ly and one late in the growing season.