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

Authors: RUTHERFORD, WILLIAM - Bureau Of Land Management; Williams, Christopher; SPAETH, KENNETH - Retired Non ARS Employee; McCord, Sarah; Hedrick, Andrew; LAURENCE-TRAYNOR, ALEX - Bureau Of Land Management

Submitted to: Dataset
Publication Type: Database / Dataset
Publication Acceptance Date: 7/17/2026
Publication Date: 7/17/2026
Citation: Rutherford, W.A., Williams, C.J., Spaeth, K., Mccord, S.E., Hedrick, A., Laurence-Traynor, A. 2026. Distribution and ecohydrologic function of pinyon pine and juniper communities and species using national longitudinal surveys. Dryad. https://doi.org/10.5061/dryad.xgxd254x4.
DOI: https://doi.org/10.5061/dryad.xgxd254x4

Interpretive Summary: Pinyon and juniper woodlands are expanding in many parts of the western United States, raising concerns about their effects on rangelands, wildlife habitat, water resources, and livestock forage. While factors such as changes in fire frequency have influenced woodland expansion, less is known about the environmental conditions that determine where different pinyon and juniper species occur and how increasing tree cover affects ecosystem health. To better understand these patterns, we analyzed field data collected from monitoring plots across the western United States between 2009 and 2021. By combining information from several long-term monitoring programs, we developed models that mapped the distribution of pinyon-juniper communities and individual tree species and identified the climate factors most strongly associated with their occurrence. Our results showed that seasonal temperature and precipitation patterns were the primary drivers of where pinyon-juniper woodlands occur and which species are present. The models accurately identified many woodland types and species distributions across the region. We also found that as pinyon and juniper density increased, plant diversity declined, perennial grasses and forbs became less abundant, and the amount of bare ground increased. These changes can reduce the land's ability to capture and retain water, increase the risk of soil erosion, and lower the availability of forage for livestock and wildlife. For ranchers, land managers, and other agricultural stakeholders, these findings provide valuable information for identifying areas at risk of woodland encroachment and declining rangeland condition. The results can help guide management decisions aimed at maintaining productive grazing lands, conserving soil and water resources, and sustaining healthy ecosystems across the western United States.

Technical Abstract: Pinyon (Pinus spp.) and juniper (Juniperus spp.) woodlands are widespread across the western United States and have undergone repeated periods of expansion and contraction over time, creating the potential for substantial changes in ecosystem structure and ecohydrologic processes. Although anthropogenic influences such as altered fire regimes have contributed to woodland dynamics, the bioclimatic and topo-edaphic factors governing pinyon-juniper (PJ) establishment and the distribution of individual species remain incompletely understood. In addition, existing satellite-based remote sensing approaches have limited capacity to detect species-specific patterns and fine-scale indicators of ecosystem function at the plot level (=30 m^2). Using ground-based vegetation plot data collected between 2009 and 2021, we developed regional models of contemporary PJ community types and species distributions across the western United States by integrating multiple long-term inventory and monitoring programs. We also evaluated environmental factors associated with the occurrence of PJ communities and individual species, and assessed potential changes in ecohydrologic function relative to pre-settlement conditions across gradients of increasing tree density. The PJ community random forest classification model achieved an overall accuracy of 61.6%, whereas species-level models ranged from 52% to 99% accuracy. Key predictors of PJ community occurrence included wet-season temperature, precipitation seasonality, warm-season precipitation, drought-season temperature, and isothermality. Among individual species, total warm-season precipitation, wet-season temperature, and precipitation seasonality were consistently important variables distinguishing species distributions. Increasing PJ density was associated with lower plant species richness, reduced perennial grass and forb cover, and greater bare ground exposure. These vegetation shifts indicate declining ecohydrologic function and a heightened risk of soil erosion. Collectively, our findings suggest that increasing PJ abundance may reduce understory diversity, diminish forage resources for livestock and native herbivores, and accelerate soil loss where disturbance and management interventions are absent. The integration of multiple national-scale monitoring programs provides a robust framework for evaluating ecosystem conditions and species-level dynamics across both natural and working landscapes.