Breeding bird community response to pinyon-juniper encroachment dynamics in eastern Nevada

Single-leaf pinyon pine (Pinus monophylla) and Utah juniper (Juniperus osteosperma) expansion is altering historic sagebrush communities in eastern Nevada. Dramatic increases in tree density have resulted in losses of sagebrush habitat and associated species. Vegetation predictor variables and breeding bird response parameters were sampled for three levels of encroachment. Results demonstrated that a decline in herbaceous and shrub cover and shrub density correlated with increasing pinyon juniper tree cover and density (P = 0.032, r2 = 0.56; P = 0 < 0.001, r2 = 0.86; and P = 0.003, r2 = 0.72). In developing a model to predict the response of birds to encroachment, juniper density and cover, total tree cover, understory cover, and shrub cover were good predictors of bird species richness. Bird density was highly variable between years, but did correlate strongly with pinyon pine cover. Birds responded to encroachment dynamics by increasing in the initial stages of encroachment, but as sagebrush and its associated species were lost, both richness and density decreased.