Long-term effects of chaining treatments on vegetation structure in piñon–juniper woodlands of the Colorado Plateau

Abstract

Over the last half-century a range of methods have been utilized to reduce trees and shrubs in order to reduce wildfire risk and promote herbaceous vegetation to support livestock and wildlife. We examined the long-term (20–40year) effects of past tree-reduction treatments on vegetation and ground cover in piñon–juniper woodlands, which is the third most extensive vegetation type in the continental United States. Tree-reduction treatments were conducted between 1963 and 1988 in Grand Staircase-Escalante National Monument, Utah by the US Bureau of Land Management and involved chaining followed by seeding to remove trees and often shrubs. Treatments were effective at increasing perennial grass cover and reducing tree cover over multiple decades. The increase in perennial grass cover was predominantly due to a nonnative species that was seeded, Agropyron cristatum (crested wheatgrass). Surface fuel loads were nearly twice as high in treated areas, likely changing fire behavior and increasing habitat complexity. Treated areas had higher bare mineral soil cover and lower biocrust cover, which may influence soil erosional processes. Interestingly, treated areas had significantly less Pinus edulis (piñon pine) recruitment compared to untreated areas, while there was no change in Juniperus osteosperma (Utah juniper) recruitment. These results indicate that treated areas may become more J. osteosperma dominated in the future due to increased establishment of J. osteosperma compared to P. edulis. Our results show that while treatments were effective at reducing tree cover and increasing herbaceous cover, there were long-term (40year) treatment effects on vegetation composition and ground cover that need to be taken under consideration when developing future management strategies.