Warming environmental conditions are often credited with increasing Arctic shrub growth and altering abundance and distribution, yet it is unclear whether tundra shrub expansion will continue into future decades. Water availability may begin to limit Arctic shrub growth if increasing air temperatures create drier soil conditions due to increased evapotranspiration and permafrost-thaw-induced soil drainage. However, few studies have effectively considered how dominant tundra shrub species respond to variations in both temperature and moisture. To better understand the key effects of temperature variation and soil moisture on two dominant circumpolar deciduous shrubs, we studied shrub growth along a natural landscape gradient in West Greenland, which is a region observed to be drying due to ongoing warming. We found that the growth forms of both grey willow (Salix glauca) and dwarf birch (Betula nana) were sensitive to warmer and drier conditions. For both species, increases in air temperature positively correlated with greater shrub volume, with the doubling of canopy volume due to increased woody biomass. Leaf biomass was best predicted by edaphic features including extractable ammonium, which was positively related to soil moisture, and bulk density. Warmer soils tended to be drier, suggesting that ongoing warming in the area could lead to significant water limitation. Our findings suggest that drier soil conditions might be limiting foliar production despite warming temperatures for two circumpolar dominant shrubs, Betula nana and Salix glauca, which could have wide-ranging, biome-level consequences about ongoing and predicted shrub growth and expansion.

北极灌木丛的增加生长和丰度和分布的变化常常被认为是环境条件变暖的原因，但尚不清楚苔原灌木丛的扩张是否会持续到未来几十年。如果由于蒸散量增加和多年冻土融化引起的土壤排水增加而使气温升高而导致土壤条件较干燥，则水的可用性可能开始限制北极灌木的生长。但是，很少有研究有效地考虑到优势苔原灌木物种如何响应温度和湿度的变化。为了更好地了解温度变化和土壤水分对两种优势圆极落叶灌木的关键影响，我们研究了西格陵兰西部沿自然景观梯度的灌木生长，该地区由于持续变暖而观测到干燥。柳（Salix glauca）和矮桦（Betula nana）对温暖和干燥的条件敏感。对于这两个物种，由于木本生物量的增加，气温的升高与更大的灌木丛数量成正相关，并且与冠层容积成倍增加。叶片的生物量可以通过包括可萃取铵盐在内的易消化特性来预测，后者与土壤水分和堆积密度呈正相关。较暖的土壤往往更干燥，表明该地区持续的变暖可能导致严重的缺水情况。我们的研究结果表明，尽管两个圆极优势灌木Betula nana和Salix glauca的温度升高，但干燥的土壤条件仍可能限制叶片的生产。，这可能会对灌木丛的持续生长和预计生长产生广泛的生物群落影响。