Multiple factors controlling polar willow growth in the high Arctic (Svalbard): Implications for future prediction of tundra productivity

Arctic regions are warming faster than the global average, leading to significant changes in permafrost, vegetation dynamics, and soil nutrient availability. Understanding these interactions is essential for predicting the rapidly changing behavior of tundra ecosystems. In central Spitsbergen, we examined the growth of Salix polaris across various elevations to assess the impact of local habitat conditions and climate change. The results obtained indicate heterogeneous growth of this species. Dendrochronological analyses revealed that low-elevation valley-bottom sites showed a strong positive correlation between June temperatures and ring growth (r = 0.69), supported by high soil moisture (up to 70 %) and nutrient-rich soils. These areas exhibited higher productivity, referred to as 'greening,' with Normalized Difference Vegetation Index (NDVI) values reaching approximately 0.5. However, increased rain-on-snow (ROS) events and rapid soil drainage caused a late summer drought. In contrast, higher elevations experienced delayed yet sustained growth in mid-to-late summer, supported by permafrost moisture retention despite colder early summers. NDVI values at high elevations ranged from 0.0 to 0.15, with soil moisture peaking around 40 %. The varied growth responses underscore the necessity of integrating multiple factors, such as soil chemistry, geomorphology, moisture variability, high-resolution imagery, and dendroclimatology, into predictive models. Relying solely on summer warmth is insufficient for understanding the complex growth behaviors in high-Arctic regions. Comprehensive approaches are necessary to accurately forecast future vegetation shifts and their ecological impacts in the High Arctic. • Growth of dwarf shrubs is strongly related to the local micro-habitat variability. • Increased temperatures in the Arctic can have a various impact on plant growth. • Depending on the altitude, a varying incremental response of the shrubs is observed • Plants growing at lower altitudes are more susceptible to drought stress. • Soil characteristics can modify the growth of dwarf shrubs but are not decisive.