Path estimates, p-values, and standardized path estimates for structural equation models (SEMs) evaluating the causal effects of changes in climate and fire history from 1986-2023 on PFG versus AFG cover for not burned and burned sagebrush (Artemisia sp.) associations

The causal effects of changes in climate and shrub and tree cover (predictor variables) on PFG cover and AFG cover (response variables) were determined using piecewise SEMs (piecewiseSEM; Lefcheck, 2016) for not burned and burned sagebrush (Artemisia sp.) associations.  PFG cover (response variable) was conditioned on (predicted by) AFG cover. Path estimates, p-values, and standardized path estimates were calculated for each set of predictor and response variables. SEMs were executed for not burned and burned areas within sagebrush associations and dashed lines (--) indicate that a predictor variable was not included in either the not burned or burned SEM. Jenks Natural Breaks were used to identify the “top” significant climate path coefficients for each SEM and the top two of three breaks are indicated with an asterisk. The sagebrush associations were from Chambers et al. (2023, 2024). Separate SEM models were fit for sagebrush associations with the largest extents within three U.S. EPA ecoregions (US EPA, 2024): Wyoming big sagebrush in Snake River Plain; Wyoming/basin big sagebrush and black sagebrush in Central Basin and Range; and low sagebrush and mountain big sagebrush in Northern Basin and Range. Descriptions of the climate, fire history, and functional group variables used in the SEMs are in Table 1. AFG = annual forb and grass; PFG = perennial forb and grass.