Plant species diversity in a grassland plant community: evidence for forbs as a critical management consideration

Authors

Monica L. Pokorny, Montana State University, Bozeman
Roger L. Sheley, Montana State University, Bozeman
Tony J. Svejcar, USDA–ARS, Burns, Oregon
Richard E. Engel, Montana State University, Bozeman

Abstract

This study quantified species and functional group diversity in a grassland plant community in southwestern Montana. Specific objectives were to measure the richness and density of functional groups within the grassland community, measure the biomass of each functional group, and calculate diversity indices for each functional group. We hypothesized that diversity would be greater than previous descriptions for the Festuca idahoensis/Agropyron spicatum habitat type because our multiple-season method would recognize seasonal and environmental variations in community composition. Of the species present, we hypothesized that forb functional groups account for the majority of richness and biomass of this grassland plant community. Species richness and density were measured during spring, summer, and fall of 2000, and biomass was collected during spring, summer, and fall of 2001. Species richness was measured by counting all species present on 4-m² plots. We measured forb density per 4-m² plot and determined grass density by counting tillers per species within a 0.2–0.5-m frame. Diversity indices were calculated for each functional group. Biomass by functional group was clipped from three 0.2–0.5-m frames per 4-m² plot. Data support the hypothesis that multiple-season sampling recognizes greater species diversity at one location because both sites were more diverse plant communities than previously described for this habitat type. We documented 14 graminoids and 69 forbs from just 2 sites. Total diversity of a 4-m² plot averaged 42 species, consisting of 5 grasses, 12 deep-rooted forbs, and 25 shallowrooted forbs. Our data also support the hypothesis that forb functional groups represent the majority of the richness and biomass of the grassland community. Forbs account for 83% of species richness in this research. In addition, forbs represent a greater proportion of plant biomass than grasses on our sites. Functional group diversity and forb diversity should be a larger consideration in Festuca idahoensis/Agropyron spicatum grassland management decisions. We recommend that land managers recognize forb species and forb functional group diversity in grassland classifications. Maintaining diversity should be a primary objective of land managers because increased diversity has been found to increase community stability and productivity, and decrease the risk of invasion by undesired species. To encourage land managers to put more resources into monitoring diversity, a simple and repeatable sampling procedure applicable to both community and landscape scales needs to be developed.

Recommended Citation

Pokorny, Monica L.; Sheley, Roger L.; Svejcar, Tony J.; and Engel, Richard E. (2004) "Plant species diversity in a grassland plant community: evidence for forbs as a critical management consideration," Western North American Naturalist: Vol. 64: No. 2, Article 9.
Available at: https://scholarsarchive.byu.edu/wnan/vol64/iss2/9