Question: Vascular plant productivity of arctic tundra has often been viewed as varying
little between years and thus being largely insensitive to the high inter-annual
variation in summer weather conditions. Yet, remote-sensing
data and retrospective
growth analyses of the circumpolar dwarf shrub, Cassiope tetragona, commonly show
considerable between-year
variability in plant growth in response to variation in
summer temperature. Given that both Cassiope growth and vascular plant biomass
production share a common environmental driver, summer temperature, we would
expect positive co-variation
between them. Here we investigate whether this is indeed
the case and if so over what spatial scale.
Location: Nordenskiöldland, high arctic Svalbard.
Methods: We brought dendroecology and plot-based
field estimation methodologies
together in an empirical study using retrospective analysis of Cassiope growth and annual
estimation of above-ground
vegetation biomass production to investigate their
temporal and spatial co-variation
and sensitivity to summer weather conditions.
Results: Despite substantial small-scale
heterogeneity, we found spatial co-variation
in Cassiope growth patterns, which weakened as distance between sampling sites
increased from 0 to 25 km. Furthermore, we found a strong positive correlation between
annual estimates of above-ground
live vascular plant biomass and Cassiope
shoot growth over a 12-year
period at a local scale. The correlation declined with
distance, likely due to increasing differences in local weather conditions.
Conclusions: We demonstrate that Cassiope growth can be used as a proxy for above-ground
tundra vegetation productivity at the local scale. Our findings suggest that
Arctic plant productivity is as sensitive to between-year
variation in summer temperature
as the well-established
growth response of Cassiope. This challenges the view that
tundra plant productivity varies little between years and provides a mechanistic understanding
that helps reconcile field-and
satellite-based
annual estimation methods.
K E Y W O R D S
Arctic bell-heather, arctic climate change, Cassiope tetragona, dendrochronology, plant–
climate interaction, spatial scale, Svalbard, tundra vegetation, vascular plant productivity,
vegetation biomass
