Growing season extension and delayed senescence: phenological responses to altered snow regimes and nutrient enrichment in High Arctic tundra species

Abstract

Arctic ecosystems are experiencing rapid changes in climate conditions, with a shift in snow regimes and nutrient availability, likely to impact plant phenology and productivity. This study investigates how increased snow depth and nutrient enrichment influence the timing of phenological phases and length of the growing season in tundra vegetation in Adventdalen, Svalbard. A factorial field experiment was established using snow fences to manipulate snow depth and fertilizer addition to simulate increased nutrient input. To assess treatment effect, phenological development was tracked in five plant species: Dryas octopetala, Salix polaris, Luzula confusa, Bistorta vivipara, and an overall “Grass” group was observed. Phenological development was monitored throughout the 2024 growing season using visual greenness estimates, NDVI (Normalized Difference Vegetation Index) measurements, and soil moisture observations across three treatments: Nutrient, Water, and Snow Fence, compared to an untreated Control.

Results showed that snow accumulation and nutrient addition had a distinct effect on plant phenology. The strongest treatment responses were observed during the senescence phase, where both Snow Fence and Nutrient treatments exhibited delayed autumn senescence and extended growing season compared to the Control. This suggests that many Arctic tundra species may prolong their active growth period when exposed to later melt-out or increased nutrient availability. In contrast, green-up was delayed by accumulated snow depth, while nutrient addition had little effect early in the season. Species differed in the magnitude and direction of their responses, with some, particularly graminoids, showing a greater phenological flexibility than others. NDVI measurements supported these findings by reflecting a prolonged season in the Snow Fence and Nutrient Treatment.

These findings demonstrate that snow and nutrient manipulations have distinct phase-specific effects on plant phenology and that species display a clear difference in their capacity to respond. This variability may lead to a shift in community composition and ecosystem function under further climate scenarios in the Arctic.