PS 38-48 - Long-term, natural recovery of mowed plant communities in the big sagebrush steppe

Abstract: Implementing restoration treatments that reduce fire risk, control for invasive species, and maintain herbaceous understories in big sagebrush ecosystems is a major conservation challenge in the western United States. Studies have found that mowing big sagebrush may reduce woody fuels and promote herbaceous understories, but a consensus on the long-term benefits of big sagebrush reduction remains unclear. In addition, few studies have documented trends in mowed big sagebrush ecosystems without intervention. With a well-established time-series (20 years) of mowed treatments in the San Luis Valley of Colorado, we addressed this knowledge gap to document long-term, natural recovery of big sagebrush plant communities. We compared plant community composition and cover, big sagebrush density and mortality, and soil texture on 46 treated and untreated plots across the study area in the summer of 2022. At each 10x10 m plot, we used 30 20x50 cm quadrats and 100 line point intercept points to estimate plant composition and cover. We counted all shrubs within half of the plot and ranked them by size class and percent dead. To estimate the influence of soil texture on plant community response, we collected soil samples from three locations in each plot at depths of 0-10, 10-20, and 20-30 cm. Our results showed that big sagebrush recovered (mean absolute live cover 17%) after 10-15 years, with no significant difference in density (p = 0.66) between treated areas and paired control sites. Perennial grass cover exceeded untreated control plot levels 1-5 years after treatment but decreased afterwards. Overall, there was an insignificant difference between change in perennial grass cover and years since disturbance (r = -0.32, p = 0.14). Perennial forb cover significantly decreased overtime since treatment (r = -0.51, p = 0.014). Our results show that big sagebrush individuals can recover after mechanical damage. Mowing does not kill most individuals and some aboveground biomass is left intact after treatment. Perennial grass cover returns to pre-treatment levels 1 to 5 years after mowing and surviving big sagebrush individuals re-establish their dominance after 10-15 years. Our results underscore the resilience of big sagebrush to partial canopy removal and emphasize the long-term dynamics following treatment.