DOI: 10.5061/dryad.90d2g
title: Data from: Winter warming effects on tundra shrub performance are species-specific and dependent on spring conditions

description: 1. Climate change driven increases in winter temperatures positively
 affect conditions for shrub growth in arctic tundra by decreasing plant
 frost damage and stimulation of nutrient availability. However, the extent
 to which shrubs may benefit from these conditions may be strongly
 dependent on the following spring climate. Species-specific differences in
 phenology and spring frost sensitivity likely affect shrub growth
 responses to warming. Additionally, effects of changes in winter and
 spring climate may differ over small spatial scales, as shrub growth may
 be dependent on natural variation in snow cover, shrub density and
 cryoturbation. 2. We investigated the effects of winter warming and
 altered spring climate on growing-season performance of three common and
 widespread shrub species in cryoturbated non-sorted circle arctic tundra.
 By insulating sparsely vegetated non-sorted circles and parts of the
 surrounding heath with additional snow or gardening fleeces we created two
 climate change scenarios: Snow addition increased soil temperatures in
 autumn and winter and delayed snowmelt timing without increasing spring
 temperatures, whereas fleeces increased soil temperature similarly in
 autumn and winter, but created warmer spring conditions without altering
 snowmelt timing. 3. Winter warming affected shrub performance, but the
 direction and magnitude were species-specific and dependent on spring
 conditions. Spring warming advanced, and later snowmelt delayed canopy
 green-up. The fleece treatment did not affect shoot growth and biomass in
 any shrub species despite decreasing leaf frost-damage in E. nigrum. Snow
 addition decreased frost damage and stimulated growth of V. vitis-idaea by
 approximately 50%, while decreasing in B. nana growth (P &lt; 0.1).
 All of these effects were consistent in the mostly barren circles and
 surrounding heath. 4. Synthesis. In cryoturbated arctic tundra, growth of
 V. vitis-idaea may substantially increase when a thicker snow cover delays
 snowmelt, whereas in longer-term, warmer winters and springs may favor E.
 nigrum instead. This may affect shrub community composition and cover,
 with potentially far-reaching effects on arctic ecosystem functioning via
 its effects on cryoturbation, carbon cycling and trophic cascading. Our
 results highlight the importance of disentangling effects of winter and
 spring climate change timing and nature, as spring conditions are a
 crucial factor in determining the impact of winter warming on plant
 performance.
description: AbioticsSnow depth over and soil temperatures in manipulated and unmanipulated non-sorted-circles. Snowdepths have been measured from west to east at every 50 cm, at three dates in the springs of 2013 and 2014. Soil temperatures measured in the center of non-sorted circles at approximately -1 cm in the autumn-spring of 2012-2013, and autumn-mid summer 2013-2014. 'ctrl' plots are unmanipulated, 'fleece' plots were covered with gardening fleeces, and 'snow' plots had snow added by use of a stone wall catching snow.Plant_responsesCanopy greenness, frost damage, shoot biomass and shoot length growth (cumulative an interpolated). Canopy greenness was measured on 8 occassions during the spring of 2014. Greenness is expressed per % of maximum greenness. Frost damage measured at two dates in late spring as relative electrolyte leakage (%). Shoot biomass (mg) at the peak of the growing season (mid-July 2014). Shoot length growth (cm) measured at 8 consecutive dates in the summer of 2014, and cumulative length growth at the peak of the growing season (mid-July 2014). Measurements are for shrub species: 'Betula' (nana), 'Vaccinium' (vitis-idaea) and 'Empetrum' (nigrum). In all files 'Inner' and 'Outer' relate to non-sorted-circle inner and outer domains. 'Control' or 'ctrl' represents unmanipulated plots, 'fleece' plots covered with gardening fleeces from autumn to late spring, and 'snow' for plots where snow was added by using a stone wall.