Recovery of rare plant populations and species richness on a calcareous floodplain in southwestern Montana

Abstract

Alkaline wet meadow and fens are exceptionally species rich and are rarely found in large river floodplains in the western US. The O'Dell Creek floodplain in southwestern Montana is fed by a series of spring creeks and contains a gradient of extremely rich to rich fen and alkaline or saline meadows and wetlands. Stream channel restoration included restoring original channel morphology and contours impacted by incision or water diversion to restore hydrologic connectivity from spring creek tributaries and floodplain wetlands to the Madison River. Active restoration methods included stabilizing incised streambanks, placement of borrowed wetland sod, and creating backwater channels and pools, while passive methods resulted in restored groundwater flow and a raised water table. Four rare wetland plant taxa were monitored over a 5-y period in active and passively restored stream sections. Total species richness increase was monitored over an 11-y period. Both active and passive techniques have resulted in the recruitment and regeneration of rare wetland plant species. At 5 y, passively restored stream terrace plots had greater species richness than found in reference plots. At 11 y, actively restored plots had attained 77% of species richness found in disturbed reference plots and 73% in undisturbed plots. Results emphasize the importance of protecting and restoring headwater, cold spring-fed wetlands to perpetuate rare and endemic plant taxa and regional wetland biodiversity, and of identifying riverine spring creek headwater wetlands with reliable groundwater as priority wetland conservation sites.