Data from: Declining temperature and increasing moisture sensitivity of shrub growth in the Low-Arctic erect dwarf-shrub tundra of western Greenland

Evergreen dwarf shrubs respond swiftly to warming in the cool and dry High
Arctic, but their response in the warmer Low Arctic, where they are
expected to be outcompeted by taller species under future warming, remains
to be clarified. Here, 12,528 annual growth increments, covering 122 years
(1893-2014), were measured of 764 branches from 25 individuals of the
evergreen dwarf shrub Cassiope tetragona from a Low-Arctic erect
dwarf-shrub tundra site in western Greenland. In addition, branch
initiation and mortality frequency time series were developed. The
influence of seasonal climate and correspondence with fluctuations in
regional normalized difference vegetation index (NDVI), a satellite proxy
for vegetation productivity, were studied. Summer temperatures were the
main driver of growth, while winter temperatures were the main
non-summer-climate driver. During past and recent warm episodes, shrub
growth diverged from summer temperatures. In recent decades, early summer
precipitation has become the main growth-limiting factor for some
individuals, likely through micro-topography-determined soil moisture
availability, and more than half of the shrubs studied became irresponsive
to summer temperatures. There was correspondence between climatic drivers,
C. tetragona growth and branch initiation frequency, and
satellite-observed vegetation productivity, suggesting the area’s
shrub-dominated tundra vegetation is limited by similar climatic factors.
Winter warming events were likely the predominant cause of branch
mortality, while branching increased after years of poor growth and
cooler-than-average summers. Synthesis: These findings show that the erect
dwarf-shrub tundra in the Low Arctic has already and will likely become
decreasingly temperature- and increasingly moisture-limited and that
winter warming supports shrub growth, but increased extreme winter warming
event frequency may increase branch mortality and vegetation damage. Such
counter-acting mechanisms could offer an explanation for the vegetation
stability observed over large parts of the Arctic.