Long-term reduced snow limits leaf gas exchange in three dominant species of moist acidic tundra in northern Alaska

Background/Question/Methods   

We examined the impacts of long-term (14 year) snow manipulations and summer warming on the leaf gas exchange, canopy structure, and ecosystem process in the moist acidic tundra of northern Alaska.  Unique to our study design was the inclusion of a reduced snow treatment.  The results from this treatment provide insights into understanding the impacts of spatial heterogeneity of snow accumulation under current conditions as well as understanding how long term projections of reduced snow in the Arctic may impact tundra ecosystems.   

We measured leaf gas exchange and stable isotopes of three dominant tundra species as well as canopy leaf area index and heights, thaw depths and soil N. Measurements took place in plots located in ambient snow, added snow created by a snow fence, and a low snow zone created in the lee of the snow fence.  The impacts of long term summer warming were measured through the use of open top chambers located in the added and ambient snow.   

Results/Conclusions

Experimental reductions in snow depth consistently resulted in lower rates of leaf carbon and water exchange in the three dominant plant species of arctic tussock tundra.  For example maximum photosynthetic capacity was lower in the low snow zone than in all other treatments including the ambient snow by up to 30%.   Leaf area index and canopy height in reduced snow were lower than other treatments but did not differ from ambient snow levels.  Summer thaw depths were greatest in areas with added snow and shallowest in reduced snow- highlighting the importance of winter time snow accumulations to tundra ecosystems.   Reductions in leaf gas exchange appear to be associated with lowered soil temperatures and reduced N in the low snow zone.

Our results support previous work on the importance of snow to tundra plant communities but are unique it that they provide insights into the heretofore unstudied impacts of the role of reduced winter snow on tundra ecosystems.  An understanding of the role of reduced snow cover could contribute to a more complete understanding of spatial heterogeneity in tundra structure and composition associated with snow accumulation patterns.  It can also help to project how predicted decreases in snow fall may impact tundra ecosystems.