Functional group and species responses to precipitation in three semi-arid rangeland ecosystems

The objective of this study was to compare forage production and foliar and basal cover responses of plant communities, plant functional groups, and individual species between years with below average (2004) and well above-average (2005) spring precipitation in three semi-arid rangeland ecosystems (shortgrass steppe, northern mixed-grass prairie, and sagebrush grassland). Foliar and basal cover at the time of a peak standing crop were visually estimated using modified Daubenmire cover categories, and forage production by species was harvested from areas that had been excluded from large herbivores. Responses of forage production to precipitation, but not foliar and basal cover, were similar for the three semi-arid ecosystems. Total forage production was more responsive (75-159%) than basal (8-35%) or foliar (2-29%) cover to increasing precipitation. Absolute (1016 kg center dot ha(-1)) and relative (159%) increases in total forage production from 2004 to 2005 were greatest for the shortgrass steppe. Forage production increases were largely attributable to greater production by C3 perennial graminoids in each ecosystem; increases in basal and foliar cover for this plant functional group were observed in shortgrass steppe and sagebrush grassland, but not in northern mixed-grass prairie. Fine-scale inputs of species and plant functional group responses to precipitation will further the accuracy of forage prediction models in predicting both total biomass production and relative proportions of plant biomass.