Habitat relations of Corydalis aquae-gelidae, a rare riparian plant

The relationships between the environment and the abundance of Corydalis aq uae-gelidae, an herbaceous perennial and a USFWS species of concern, were e xplored. Information concerning habitat relations was pursued to determine possible conservation measures. Corydalis grows in headwater streams, up to 1300 m elevation, and down to 585 m on the fifth order Clackamas River, Mt . Rood National Forest, Oregon. Occupied streams had smaller seasonal flow fluctuations than streams where the species was absent, and had summer air and substrate temperatures averaging 17.7 C and 10.6 C, respectively. Coryd alis abundance in plots was related to the distance to the summer water lev el, substrate texture and organic matter content, and plant community compo sition. Optimal conditions were identified coarse moss-covered, mineral sub strates within 15 cm of the summer water level. Fine (<2 mm) or organic sub strate material reduced Corydalis abundance. On the Oak Grove Fork, about 7 5% of the plants grew between the average winter high and summer low water level, an estimated vertical distance of 25 cm. The results were useful for management, and underscored. the need to maintain stable hydrological cond itions, avoid sedimentation, and protect riparian areas.