Sagebrush steppe is critical habitat in the Great Basin for wildlife and provides important ecosystem goods and services. Expansion of pinyon (Pinus spp.) and juniper (Juniperus spp.) in the Great Basin has reduced the extent of sagebrush steppe causing habitat, fire, and forage concerns. An instrumented watershed, Porter Canyon Experimental Watershed, was established to address the hydrologic and ecological effects of pinyon and juniper expansion and treatments to reduce tree density. We examined changes in seasonal and spatial plant phenology that have important implications for ecological dynamics. Images from land-based plant phenology cameras were analyzed with the R statistical software Phenopix package to extract indices of plant greenness (GCC) and normalized difference vegetation index (NDVI) for sagebrush steppe, meadows and woodland areas. Available land-based images spanned three years, 2014-2016. The new cloud-based ClimateEngine.org application was used to compute and extract NDVI from Landsat imagery, to compare indices from land-based camera measurements with remotely-sensed data. Transpiration of pinyon, juniper and mountain sagebrush (Artemisia tridentata subsp. vaseyena ) was measured with thermal-heat dissipation techniques. Environmental variables were measured with standard equipment for soil water content, snow depth, groundwater and meteorological variables.
Results/Conclusions
Mountain sagebrush phenology was strongly influenced by topographic position and weather. In 2014, sagebrush started green-up 14 days earlier and peak vigor was 21 days earlier during dry/warm conditions. In 2015, with below average precipitation but more persistent snow, phenology was delayed and GCC increased. Transpiration measured on individual stems ranged from 2.5-6 L-day-1 during peak GCC. Landsat NDVI was well correlated to GCC. For the meadow, spatial analyses of land-based NDVI revealed distinct differences in meadow phenology between wet, mesic and dry areas driven by groundwater depth and air temperature. The increased temporal and spatial resolution provides detailed information on critical habitats. Landsat NDVI from 2009 – 2017 tracked closely with groundwater levels in the meadow, and captured the effects of an El Niño oscillation, that produced drought followed by two wet winters. GCC and phenophases of evergreen pinyon and juniper were also able to be extracted. Exploratory analyses of NDVI on the evergreen tree canopies and concurrent transpiration rates are being conducted. There has been a recent advent of phenology and camera networks worldwide. These analyses demonstrate the utility of land-based imagery and remotely-sensed imagery to quantify plant phenology and phenophases in semi-arid cold desert regions.