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Distribution and ecohydrologic function of pinyon pine and juniper communities and species using national longitudinal surveys

Rutherford, William12; Williams, C. Jason3; Spaeth, Kenneth4; McCord, Sarah3; Hedrick, Andrew3; Laurence-Traynor, Alex2

Published Jul 17, 2026 on Dryad. https://doi.org/10.5061/dryad.xgxd254x4

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Abstract

Pinyon (Pinus spp.) - juniper (Juniperus spp.) woodlands are a common ecosystem type across the western USA that have historically and are actively experiencing expansion and contraction with risk of ecosystem alteration in ecohydrologic function. Excluding anthropogenic influences on ecosystem development (e.g., alterations to historical fire regimes), the specific bioclimatic and topo-edaphic determinants of PJ woodland establishment, especially the species that comprise them, are poorly understood. Assessment of species-level dynamics with on-the-ground (e.g., ≤ 30 m2) indicators of ecosystem functioning is difficult with available satellite remote sensing techniques. Using ground-based plot samples, we present current (2009-2021) PJ community and species regional domains modeled from multiple longitudinal assessment and monitoring frameworks across the western USA with potential factors driving or controlling their presence. We further evaluated the ecohydrological function of PJ communities relative to pre-settlement conditions as tree densities increase and those regions where functioning may be changing. Our PJ community/ecosystem random forest classification model had an accuracy of 61.6% with species-level models ranging from 52% to 99%. The top model determinants of PJ community ecosystems were wet-season temperature, precipitation seasonality, warm-season precipitation, seasonal drought temperature, and isothermality. Total warm-season precipitation, wet-season temperature, and precipitation seasonality were among the top discriminant variables between PJ species. High PJ densities were associated with reduced species richness and total perennial grass and forb cover with consequence of increasing bare ground cover, inducing the potential for soil surface erosion (e.g., reduced ecohydrologic function). Taken together, increasing PJ species density and cover can come at the risk of loss of plant understory richness, livestock and native herbivore forage, and surface soils in absence of management intervention or fire. These national longitudinal surveys provided valuable ecosystem- and species-level detail to assess trends in both natural and agricultural resources.