Simulating sagebrush–cheatgrass plant community biomass production in the Great Basin using ALMANAC

Abstract

Cheatgrass (Bromus tectorum) is a widespread species of concern throughout the western US, as it dominates many low-elevation rangelands and continues to spread annually. As a winter annual grass, however, cheatgrass can produce high-quality and cheap protein forage for livestock early in the growing season. Estimating biomass can lead to better management in these western United States and Great Basin plant communities. The present study was designed to evaluate the accuracy of biomass simulations in Great Basin plant communities using the process-based Agricultural Land Management Alternative with Numerical Assessment Criteria (ALMANAC) model as it simulates biomass production and competing species interactions. For this study, data were used from the Sagebrush Steppe Treatment Evaluation Project to simulate cheatgrass, perennial grass, forb, and sagebrush biomass across three community types: native, invaded, and a co-dominated community of sagebrush, perennial grasses, cheatgrass, and forbs at six representative Great Basin sites from 2006 to 2018. Our results indicated a strong relationship between simulated and measured biomass of total cheatgrass and perennial grasses across the three plant communities. Sagebrush and forb biomass were poorly simulated across most plant community types. Model accuracy also varied by site, largely depending on elevation. We saw high variability in simulated biomass across years, likely because of the single point-in-time measurements at peak biomass and the low biomass values of cheatgrass and forbs. Collectively, ALMANAC shows potential for assessing biomass production and plant interactions but will require more data and model development to fully comprehend its utility.