Code to analyze fuel breaks and exotic annual grass associations within sagebrush ecosystems of the western USA

Methods Summary

This repository supports the manuscript "Invasion resistance varies by fuel break type in sagebrush ecosystems." The analysis evaluated the relationship between fuel break treatments and exotic annual grass cover across the sagebrush biome using two complementary approaches:

1. Space-for-Time Substitution Analysis:

We used 52,109 Bureau of Land Management AIM vegetation surveys (2004–2022) and 62 targeted field surveys (2019–2022) to assess spatial patterns of exotic annual grass cover near mowed and green strip fuel breaks. Vegetation cover was modeled using a Bayesian ordered beta generalized linear mixed model (GLMM), incorporating a three-way interaction between:
Fuel break type (mowed vs. green strip),
Treatment age (years since installation),
Distance from the fuel break.

Environmental covariates (e.g., elevation, precipitation, fire history) and random effects for year and spatial grid were included to account for confounding factors.

2. Time Series (PC BACIPS) Analysis:

We conducted a Progressive-Change Before-After Control-Impact Paired Series (PC BACIPS) analysis using 167 paired time series (1984–2022) of annual herbaceous cover from the Rangeland Analysis Platform (RAP). We compared trends at treated sites (inside, 500 m, and 1,000 m from fuel breaks) to nearby control sites, fitting step, linear, asymptotic, and sigmoidal models to detect treatment effects.

Together, these methods provide robust spatial and temporal insights into the ecological impacts of fuel break installation.