Submitted to: Rangelands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/1996
Publication Date: N/A
Interpretive Summary: The management of riparian zones has become a major focus on western rangelands. Unfortunately, managers are still lacking some of the information they need for managing riparian ecosystems. It is often assumed that riparian vegetation will regrow vigorously after grazing (either by wildlife or by livestock) because of the wet nature of these ecosystems. Regrowth is desireable because one goal of riparian management is to leave enough vegetation to protect streambanks from the high streamflows in the spring. We evaluated the regrowth potential of vegetation typical to many streams in southeastern Oregon. Our findings indicate that regrowth potential is limited after mid-summer. The study supports the early-season grazing approach advocated by a growing number of land managers, and further suggests that we might need to revaluate the assumptions often made about regrowth of riparian vegetation following grazing.
Technical Abstract: In recent years, the interest in management of riparian zones has increased dramatically. Unfortunately, we are still asking relatively fundamental questions about how riparian systems function. There is considerable debate about the amount of regrowth that can be expected after a summer grazing period. The assumption is often made that riparian areas, because of the moisture regime, will experience considerable regrowth during the summer and early fall. This study was designed to quantify the amount of regrowth occurring on a stream-associated riparian zone in southeastern Oregon following defoliation. During three consecutive years, riparian vegetation was clipped either mid-June, mid- July, mid-August, or mid-September. Regrowth was measured mid-October for each of the treatments. There was very little regrowth of the riparian community if clipping occurred after mid-July. For example, regrowth in September was less than 1% of total standing crop, and regrowth in August and September combined contributed less than 5% to total standing crop. Our study included a year that set the all-time recorded high for yearly precipitation and snowpack and yet there was still limited late summer growth. Managers should be cautious in their assumptions about regrowth in riparian areas. We have often assumed that because riparian areas are relatively wet, they will regrow vigorously. The amount of regrowth will undoubtedly depend on the plant community, elevation, and the hydrology of the site. However, under the conditions of this study significant regrowth after mid-summer would not be expected.