UC Merced

Meadows in the Western U.S. are greatly valued for their ecological and socioeconomic functions. Yet, they are subject to multiple stressors, which can result in loss due to degradation. In the Sierra Nevada, seasonally wet meadows are vulnerable to potentially significant damage by recreational pack stock use, when soil water content is high and vegetation is developing. On federally managed lands, meadow degradation from pack stock use is of significant concern. My study provides an investigation of ecological influences on spatial variability in meadow vulnerability to disturbance, as measured by soil resistance (SR). I examined SR on both local and site scales, by plant community type and meadow gradients class. My research addressed two ecological questions: 1) Does SR, and potential ecological influences on SR, significantly differ among plant community types and meadow gradient classes?; and 2) Can a few key ecological factors best explain variation in SR among meadow plant community types? My findings suggest that SR is a robust indicator of vulnerability to disturbance by recreational pack stock use. When stratifying by plant community type and meadow gradient class, my findings suggest that SR, and ecological influences on SR, significantly differed on local and site scales. Among factors that most influenced SR, water content was identified as the key driver of variation. In addition to water content alone, a few key factors best explained spatial variation in SR among plant community types. These included bulk density, root mass, and coarse fragments. On a site-scale, soil texture and subsequent water availability (water holding capacity and water content) most significantly differed between meadow gradient classes. My results indicate that even in dry years, some plant community types, representative of Sierran meadow hydrologic regimes, cannot support pack stock use without incurring damage. This may be due to variation in water availability and other covariates of SR based on differences in meadow gradient class. My findings provide new information to help develop vulnerability indices and risk assessments that aim to inform science-based, best management practices for maintaining meadow function. This can inform determination of pack stock site suitability among seasonally wet meadows.