Avian communities are decreasing with piñon pine mortality in the southwest

Abstract

An increase in tree mortality is expected to occur worldwide due to climate-induced drought and increasing temperatures. The 2000–2002 drought in the southwestern United States was one of the most severe in the last 50 years. It led to a severe outbreak of bark beetles that resulted in high mortality of piñon pine (Pinus edulis) trees on the Pajarito Plateau in Northern New Mexico beginning in 2002. Many areas in piñon-juniper habitat had entire stands of piñon die leaving only juniper (Juniperus spp.). Point count surveys were used to determine avian responses to tree mortality from 2003 to 2013. We also tested whether birds responded differently in sites that were mechanically thinned in 2002 and 2003 on Los Alamos National Laboratory property compared to sites not thinned. Junipers and dead piñon pines due to bark beetles and drought were removed on thinned sites. Richness, diversity, and abundance steadily declined after 2003. There was a 73% decrease in abundance and a 45% decrease in richness from 2003 to 2013. There was no difference in community composition between thinned and unthinned sites. Bird abundance and species richness declined faster in thinned sites than unthinned sites, but diversity decreased similarly in both treatments. Several species disappeared over time and some declined substantially. Our results suggest a delay in bird responses to tree mortality on the Pajarito Plateau. Piñon mortality may be a significant threat to bird communities in the southwestern U.S., and tree thinning to control fire may be an added risk.