Reversing tree expansion in sagebrush steppe yields population-level benefit for imperiled grouse

Abstract

Woody plant expansion into shrub and grasslands is a global and vexing ecological problem. In the Great Basin of North America, the expansion of pinyon–juniper (Pinusspp.–Juniperus spp.) woodlands is threatening the sagebrush (Artemisia spp.) biome. The Greater Sage-grouse (Centrocercus urophasianus; sage-grouse), a sagebrush obligate species, is widespread in the Great Basin and considered an indicator for the condition of sagebrush ecosystems. To assess the population response of sage-grouse to landscape-scale juniper removal, we analyzed a long-term telemetry data set and lek counts with a Bayesian integrated population model in a before-after-control-impact design. Population growth rates (λ) in a treatment area (Treatment) with juniper removal and a control area (Control) without juniper removal indicated the two areas generally experienced population increase, decrease, and stability in the same years. However, the difference in λ between study areas indicated a steady increase in the Treatment relative to the Control starting in 2013 (removals initiated in 2012), with differences of 0.13 and 0.11 in 2016 and 2017, respectively. Retrospective sensitivity analysis suggested the dynamics in λ were driven by increases in juvenile, adult, first nest, and yearling survival in the Treatment relative to the Control. These findings demonstrate the effectiveness of targeted conifer removal as a management strategy for conserving sage-grouse populations in sagebrush steppe affected by conifer expansion. Examples of positive, population-level responses to habitat management are exceptionally rare for terrestrial vertebrates, and this study provides promising evidence of active management that can be implemented to aid recovery of an imperiled species and biome.