Livestock Exclusion Effects on the Structure and Function of Headwater Streams

Abstract

The structure and function of headwater streams was evaluated in response to livestock exclusion implemented through Virginia's Conservation Reserve Enhancement Program (CREP). We measured riparian plant characteristics along with stream organic matter dynamics, benthic macroinvertebrates, algal biomass, and leaf breakdown in non-fenced, fenced, and forested streams. Increased growth of non-woody vegetation and the pre-existence of woody plants had a significant influence on stream organic matter dynamics. Tree basal area in a 20 m wide riparian corridor was predictive of stream coarse benthic organic matter standing stocks. Higher benthic organic matter standing stocks and differences in algal biomass in fenced and forested sites indicate different food resources may be structuring macroinvertebrate communities in these systems. We found a significant relationship between coarse benthic organic matter and percent shredder density, and scraper density generally followed patterns of algal biomass among treatments. Leaf breakdown rates among treatments were not indicative of differences in shredder density with two of the three fenced sites having the fastest overall breakdown rates observed. We attributed faster breakdown rates in these streams to available food resources and shredder community structure existing prior to the implementation of livestock exclusion. <p> Our results suggest that a certain amount of ecological recovery may be possible through livestock exclusion. Macroinvertebrate structure in our study streams was primarily influenced by the presence or absence of riparian trees. Maturation and successional changes in woody riparian vegetation after livestock exclusion may allow certain characteristics of pastoral streams to return to those found in forested reaches.