Modelling pinyon pine distribution in the northern Great Basin, USA

Summary Pinyon-juniper woodlands are dry ecosystems defined by the presence of juniper (Juniperus spp.) and pinyon pine (Pinus spp.), which stretch over 400 000 km2 across 10 US states. Certain areas have become unnaturally dense and have moved into former shrub and grasslands, while others have experienced widespread mortality. To properly manage these woodlands, sites must be evaluated individually and decisions made based on scientific information that is often not available. Many species utilize pinyon-juniper woodlands, including the pinyon jay (Gymnorhinus cyanocephalus), named for its mutualism with pinyon pine, whose population has declined by c. 2.2% per year from 1966 to 2022, an overall decrease of c. 71%. To increase the likelihood of further research progress, we propose a tool to model the distribution of pinyon pine at a finer scale than current woodland classification tools in the northern US Great Basin: a random forest model using geographical, ecological and climate variables. Our results achieved an accuracy of 93.94%, indicating high predictive power to identify locations of pinyon pine in north-eastern Nevada, the south-eastern corner of Oregon and southern Idaho. These findings can inform managers and planners researching pinyon pine, pinyon-juniper woodlands and potentially the pinyon jay.