Micro-topography
Shrubs responsive to early summer temperatures were restricted to
upslope positions, while those responsive to late summer temperatures
were found further downslope. This pattern may be related to the
redistribution of snow by wind with accumulation of snow according to
topography . In the study area, winter winds blow mainly from northern
direction , and the downslope positions may thus be more wind-sheltered
and be covered in a deeper snow layer. Upslope positions would then be
snow-free earlier, which may explain the responsiveness to early summer
temperatures found there. Upslope soils will drain and warm faster and
are thus drier, which could be the reason for the response to previous
summer precipitation of the northernmost shrub in this study. This could
also explain the negative response to previous autumn temperatures over
the period 1984-2013 of some of the upslope shrubs, with warm dry
autumns resulting in lower soil moisture availability in the following
growing season. A negative influence of autumn temperatures was recently
also observed for shoot length growth of the related boreal shrubEmpetrum nigrum , growing near its southern lowland distribution
limit in northern Germany . Over the period 1984-2013, non-responsive
shrubs were mostly found at upslope positions and shrubs responsive to
early summer precipitation sums mostly mid-slope. Shrubs at downslope
positions were mostly still responsive to late summer temperatures. This
is in line with the expected gradient in snow depth.