THE ROLE OF BEAVER PONDS IN MAINTAINING RIPARIAN VEGETATION HEALTH DURING DROUGHTS: A CASE STUDY AT SUSIE CREEK AND MAGGIE CREEK, NV

Beaver damming creates and maintains riparian ecosystems throughout the American west - including riparian ecosystems in arid climates afflicted by seasonal and multi-year droughts. We hypothesized that beaver ponds act as buffers against the effects of drought on nearby riparian vegetation. The proposed mechanism of beaver-dam-induced drought buffering is as follows: the beaver ponds formed upstream of each dam retain water during wetter parts of the year. During drier parts of the year, the ponds gradually release water into nearby soil where it is accessible to the roots of riparian vegetation. To quantify the extent and duration of water release from beaver ponds, we calculated the evapotranspiration (ET) and normalized difference vegetation index (NDVI) of riparian vegetation in riparian areas both with and without beaver-damming. These measures of vegetation health were compared to the location and intensity of beaver damming in order to quantify the drought buffering effects of beaver ponds.

NDVI was calculated from Landsat 8 data and ET was estimated using the Mapping Evapotranspiration with Internalized Calibration (METRIC) model. We used data from 2013-2016, which includes a multiyear drought (2013-2015) as well as seasonal summer droughts at Susie and Maggie Creeks. In arid landscapes like this one with sufficient sunshine and soil nutrients, the primary reason for decreased ET/NDVI during the growing season will be lack of water. We found that the daily ET of riparian areas with beaver damming was 50-150% higher than the daily ET in riparian areas without beaver damming, and that NDVI in dammed riparian areas was 6-88% higher than in undammed areas. These differences peaked in mid-summer when the landscape is at its hottest and driest state and were overall larger during the drought years (2013-2015) than during the wet year (2016). There was no apparent loss of drought buffering capacity of the beaver ponds as the multiyear drought progressed, which suggests that the ponds are able to fully recharge each year even if the winter precipitation is also below average. Our results indicate that riparian areas with beaver damming in arid climates are better able to maintain vegetation health than areas without beaver damming during both short and extended periods of drought.