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.