Associations among topography, snowmelt, and plant green-up phenology, revealed through a time-lapse camera network

Abstract:

The brief snow-free season characteristic of alpine systems restricts access to newly emergent, highly nutritious forage by herbivores that live at high elevations. In the Sierra Nevada mountains, a high elevation range in California, bighorn sheep undergo a partial seasonal migration to low elevation “winter” habitat, where snowpack is less deep and persistent than snowpack at high elevations, to maintain forage access year-round. Satellite-derived measurements of snowmelt and vegetation growth are useful for understanding spatial patterns in landscape phenology. However, the resolution of spaceborne sensors is too coarse for investigations of green-up phenology at the species level. The data gap presented by such coarsely resolved measurements may limit investigations of forage quality and quantity, movement, population dynamics, and conservation of large herbivores.

We introduce a network of digital repeat (“time-lapse”) cameras deployed in 2018 that compiles daily imagery in the Sierra Nevada mountains of California at the sub-meter scale. We present snowmelt and plant green-up phenology data from this fine-scale remote sensing network. We identify strong associations between landscape phenology and elevation and latitude, but find that these relationships are not consistent across years. We compare spatial patterns in snowmelt and plant green-up following the precipitation-heavy winter of 2018-2019 and the “drought” winter of 2019-2020. We furthermore explore relationships among our fine-scale photography network and measurements derived from the Earth-orbiting Landsat and MODIS satellites. Finally, we discuss the roles of shifting snow and plant phenology for the endangered Sierra Nevada bighorn.