Mediating Water Temperature Increases Due to Livestock and Global Change in High Elevation Meadow Streams of the Golden Trout Wilderness

Rising temperatures due to climate change are pushing the thermal limits of many species, but how climate warming interacts with other anthropogenic disturbances, such as land use, is less well understood. We used fine-scale water temperature data to predict the effect of climate warming and livestock grazing on extreme water temperature in three high elevation meadow streams in the Golden Trout Wilderness, California. These meadows have been grazed by cattle and sheep since the 1800s and their streams are home to the imperiled California golden trout, Oncorhynchus mykiss aquabonita. Using 81 loggers monitoring water temperature between 2008 and 2013, we found that water temperatures were cooler in ungrazed meadows compared to the grazed one, and that predicted temperatures under different global warming scenarios were likely to be higher in presence of livestock. We also found that river bank vegetation (willows) was higher and denser in ungrazed zones, resulting in shadier rivers and lower maximal temperatures. Our results highlight that interactions between climate change and land use can worsen the local thermal conditions for taxa on the edge and support the idea that cattle should be removed from sensitive ecosystems.