Willow planting success as influenced by site factors and cattle grazing in northeastern California

Abstract

In recent years there has been an increasing emphasis on reestablishment of woody vegetation in degraded riparian zones. In this study we evaluated the influence of grazing and selected site factors on survival and leader growth of planted Geyer willow (Salix geyeriana Anderss.) cuttings. Three grazing treatments (early summer, late summer, and non-use) were evaluated on each of 3 streams in broad, low-gradient meadows with silt loam soils in the northern Sierra Nevada. The streams were perennial with terraces often 1.0 to 1.5 m above streambottom. Unrooted Geyer willow cuttings were planted to 30-cm soil depth in early May 1987 at 3 streamchannel locations (streambottom, streambank, and stream terrace) within each of the grazing treatments. Survival, associated community type, and cover class were determined for 2,700 plantings. Leader length and grazing intensity were measured for 694 surviving cuttings in 1988. Percent soil moisture and water table depth were determined for a subset of the willow cuttings. There was no significant (P>0.05) effect of grazing treatment on either willow survival or growth despite 3.5 to 5 times more defoliation use of the willow cuttings in the grazed pastures. Streamchannel location did significantly (P lesser than or equl to 0.05) affect willow survival (streambottom = 83%, streambank = 34%, and stream terrace = 3%) but not individual plant leader length. Survival of willow cuttings for Carex nebrascensis/Jancas nevadensis, bareground, Des- champsia caespitosa/Carex nebrascensis, and Artemisia sp. dominated sites was 76, 60, 44, and 2%, respectively. However, leader length was significantly (P lesser than or equal to 0.05) greater for bareground sites than for sites supporting vegetation. Cover class was not a good indicator of survival, but as might be expected from the results on the bareground sites, leader length for the 0-5% class was 1.8 times the length of the next class. There was a clear relationship between water table depth, soil moisture, and willow planting survival but not between moisture measurements and leader length. Once the water table has declined to the point that Artemisia sp. can survive on a site, the chances of successfully replanting willows are minimal. However, even during the drought years of this study (<50% of average annual precipitation) a survival rate of 60% or greater was achieved by planting into Carex nebrascensis communities or bareground in the streamchannel.