Avian Community Responses and Vegetation Structure Changes Following Prescribed Thinning in Pinyon-Juniper Woodlands: A Seven-Year Study in South-Central New Mexico

Pinyon-juniper woodlands occupy approximately 40 million hectares throughout the western United States and have expanded in range and density over the past 150 years. This is primarily due to fire suppression, overgrazing, and climate change. Management goals in these ecosystems focus on reducing hazardous fuel loads via mechanical thinning to enhance grass and forb cover for ungulate habitat and rangeland health. This seven-year study examined the avian community response and vegetation structure changes following mechanical thinning in pinyon-juniper woodlands of the Fort Stanton-Snowy River Cave NCA in southern New Mexico. We conducted three rounds of standardized avian point count surveys at 220 sites, 97 Control (un-thinned) and 123 Treatment (thinned) each summer from 2018 to 2024. Results revealed subtle but significant differences in avian community composition. While species richness and diversity remained similar between Managements, community analyses demonstrated that woodland species (e.g., Black-throated Gray Warbler and Mountain Chickadee) showed a preference for Control sites. In contrast, grassland species (e.g., Chihuahuan Meadowlark and Lark Sparrow) were strongly associated with Treatment sites. Distance sampling analysis found that seven woodland species showed significant density reductions in thinned sites. However, occupancy modeling results found that from 29 species, all responses to thinning were positive or neutral, suggesting current management practices effectively support a broad array of species. We also assessed multiple vegetation metrics transects at 65 sites (25 Control, 40 Treatment) during the study period. Vegetation monitoring revealed that mechanical thinning effectively altered woodland structure while promoting understory development. Treatment sites exhibited lower bare ground cover and higher foliar cover than Control sites, and canopy and basal cover exhibited a moderately negative correlation. Woody stem distribution shifted from smaller seedlings in Control sites toward medium and larger shrubs in treatment areas, with selective retention of mature trees maintaining structural diversity. These findings suggest that mechanical thinning, when implemented with habitat retention in mind, can effectively balance management objectives with conservation goals.