Hydrology, vegetation, and wet meadow restoration at Weippe Prairie, Nez Perce National Historical Park, Idaho

Schook, Derek; Borkenhagen, Andrea; Cooper, David

The Weippe Prairie unit of Nez Perce National Historical Park serves to let visitors experience the setting encountered by Lewis and Clark when they first met the Nez Perce people. In the 1805 encounter the site was a wet meadow supporting camas lily (Camassia quamash) and other native wetland plants, but over the past two centuries the landscape has been heavily altered. Land use alterations included digging drainage ditches, plowing, and introducing exotic plant species. This report summarizes our work from 2011 to 2018 analyzing the hydrologic, soil, and vegetation conditions at Weippe Prairie. It also documents hydrologic and vegetation restorations and their effects on the landscape. Study methods included a network of monitoring wells and staff gauges to track water levels through time, soil oxidation/reduction stations to measure soil redox potential, characterization of soil physical properties, and vegetation analyses. In fall 2015 we permanently filled a drainage ditch with mineral sediment, which increased ponding, delayed runoff, raised the water level, and increased the duration of plant-available water through the growing season. Native wetland species were planted on the filled ground in 2016, and seedlings successfully expanded after two growing seasons. The prairie has not transitioned from dominance by exotic pasture grasses to a native wetland assemblage, but the area that was hydrologically restored and planted appears to be on a desirable trajectory. The larger landscape at Weippe Prairie still has several artificial drainage ditches that could be targeted for future restorations, actions that would both enhance visitor experience and improve the integrity of the wet meadow ecosystem.