Plant biomass and species composition along an environmental gradient in montane riparian meadows

Abstract

In riparian meadows, narrow zonation of the dominant vegetation frequently occurs along the elevational gradient from the stream edge to the floodplain terrace. We measured plant species composition and above- and belowground biomass in three riparian plant communities-a priori defined as wet, moist, and dry meadow-along short streamside topographic gradients in two montane meadows in northeast Oregon. The objectives were to: (1). compare above- and belowground biomass in the three meadow communities; (2). examine relations among plant species richness, biomass distribution, water table depth, and soil redox potential along the streamside elevational gradients. We installed wells and platinum electrodes along transects (perpendicular to the stream; n=5 per site) through the three plant communities, and monitored water table depth and soil redox potential (10 and 25 cm depth) from July 1997 to August 1999. Mean water table depth and soil redox potential differed significantly along the transects, and characterized a strong environmental gradient. Community differences in plant species composition were reflected in biomass distribution. Highest total biomass (live+dead) occurred in the sedge-dominated wet meadows (4311+/-289 g/m(2)), intermediate biomass (2236+/-221 g/m(2)) was seen in the moist meadow communities, dominated by grasses and sedges, and lowest biomass (1403+/-113 g/m(2)) was observed in the more diverse dry meadows, dominated by grasses and forbs. In the wet and…