Piñon-juniper woodlands are one of the largest ecosystems in the United States and harbor many piñon-juniper-associated bird species. It is a common practice to reduce tree cover and density of these woodlands for various objectives, including increasing livestock forage and reducing wildfire hazard. Understanding the different pathways of how piñon-juniper thinning affects bird species of conservation concern is important for both woodland management and avian conservation and thus warrants investigation. In this study, we aimed to understand the pathways of the effects of piñon-juniper woodland thinning on bird species groups of high, moderate, and low conservation concern, as well as seven priority bird species. During the month of May from 2021 to 2023, we collected count data with distance sampling and removal sampling information from 46 1km × 1 km plots (23 treated ≤10 years previously and 23 controls). We then used these data to estimate abundance of bird species across the gradients of piñon-juniper thinning and eight environmental factors such as canopy cover. By using a path analysis based on N-mixture modeling, we were able to decompose the effects of piñon-juniper thinning on avian abundance that can be explained by the environmental factors considered or by other unmeasured factors. Our results revealed multiple pathways of the effects of piñon-juniper thinning on bird groups and species. Overall, piñon-juniper thinning had negative effects on the species group of high and moderate conservation concerns, mainly through reduced tree density and canopy cover. Piñon-juniper thinning also had negative effects on five priority species: Pinyon Jay (Gymnorhinus cyanocephalus), Woodhouse’s Scrub-Jay (Aphelocoma woodhouseii), Juniper Titmouse (Baeolophus ridgwayi), Virginia’s Warbler (Leiothlypis virginiae), Black-throated Gray Warbler (Setophaga nigrescens), and a positive effect on one priority species (Gray Vireo, Vireo vicinior), with this total effect being explained by environmental factors considered or unmeasured factors, depending on the species. Our results showed that the pathways of the effects of piñon-juniper thinning on avian biodiversity were complicated and multifaceted, and indicated that a reevaluation of thinning in piñon-juniper woodlands might be needed.
Zhao et al. (Thu,) studied this question.