Data from: Plant community-specific greening patterns predict population size increases in a temperate herbivore

Climate change driven impacts on vegetation productivity have been shown
to drive mammalian herbivore population dynamics in arctic and alpine
environments. However, there is less evidence for temperate systems. To
address this, we examined the contribution of increasing plant biomass in
different vegetation communities (measured by NDVI, normalised difference
vegetation index) and winter weather on the observed long-term upward
trend in the population of the Soay sheep of Hirta, St Kilda, UK. We found
that biomass had increased in all vegetation communities present and done
so increased fastest in vegetation types preferred by the sheep.
Specifically, those communities with high Specific Leaf Area and
Ellenberg’s N, low Leaf Dry Matter Content. Peak summer NDVI and either
winter average wind speed or winter North Atlantic Oscillation data added
to the variance explained by a simple density dependence model of yearly
sheep population growth rates. The highest explanatory power was found for
preferred vegetation types including maritime cliff communities dominated
by Plantago species, but also for both inaccessible (Rumex
acetosa-dominated) or unpreferred (Eriophorum vaginatum- or
Sphagnum-dominated) communities where seasonal variation more closely
reflects productivity due to minimal grazing. Although the climate is
getting windier and wetter, it is also getting warmer allowing increased
plant productivity and this appears to be behind the long-term increases
in the Soay sheep population. Our study indicates that analysing key
vegetation communities may reveal these links better than using
landscape-level averages, and that oceanic-temperate systems may show
similar climate-driven herbivore population trends to those reported in
arctic and alpine systems.