Disappearing green: Shrubs decline and bryophytes increase with nine years of increased snow accumulation in the High Arctic

Abstract

<i>Question</i> - How does increased snow depth affect plant community composition of High Arctic tundra, and can the Normalized Differential Vegetation Index (NDVI) detect induced changes?<p><p>

<i>Location</i> - Adventdalen, Spitsbergen, Svalbard (78°10′ N, 16°04′ E).<p><p>

<i>Methods</i> - We manipulated snow depth on the tundra using fences, resulting in <i>Deep, Medium</i>, and <i>Ambient</i> snow regimes. Increased snow led to warmer winter soil temperatures, a delayed onset of growing season and wetter conditions during the early growing season. Plant community composition of living and dead plant material was recorded after nine years. NDVI was measured at the plot level using a handheld sensor.<p><p>

<i>Results</i> - Community composition and the abundance of typically dominant shrub species were substantially different in the <i>Deep</i> compared to the <i>Ambient</i> regime. <i>Deep</i> had lower cover of live shrubs (<i>Cassiope tetragona, Dryas octopetala</i> and <i>Salix polaris</i>) and <i>Luzula confusa</i>, and higher cover of dead shrubs (<i>Cassiope</i> and <i>Dryas</i>) compared to the other snow regimes. Bryophyte cover was highest in <i>Medium</i>. NDVI was positively correlated to the cover of living vascular plants and negatively correlated to cover of dead vascular plants. Accordingly, <i>Deep</i> snow regime had reduced NDVI, reflecting the contribution of dead <i>Cassiope</i> and <i>Dryas</i>.<p><p>

<i>Conclusion</i> - Snow regime strongly influenced community composition in High Arctic plant communities. Enhanced snow regimes had more dead shrubs, reduced <i>Luzula</i> and increased bryophyte cover than ambient conditions. These differences were detectable by handheld NDVI sensors.