The response of Arctic vegetation to the summer climate: relation between shrub cover,NDVI, surface albedo and temperature

Abstract

Recently observed Arctic greening trends from normalized difference vegetation index(NDVI) data suggest that shrub growth is increasing in response to increasing summertemperature. An increase in shrub cover is expected to decrease summer albedoand thus positively feed back to climate warming. However, it is unknown howalbedo and NDVI are affected by shrub cover and inter-annual variations in thesummer climate. Here, we examine the relationship between deciduous shrubfractional cover, NDVI and albedo using field data collected at a tundra site inNE Siberia. Field data showed that NDVI increased and albedo decreased withincreasing deciduous shrub cover. We then selected four Arctic tundra study areas andcompiled annual growing season maximum NDVI and minimum albedo maps fromMODIS satellite data (2000–10) and related these satellite products to tundravegetation types (shrub, graminoid, barren and wetland tundra) and regionalsummer temperature. We observed that maximum NDVI was greatest in shrubtundra and that inter-annual variation was negatively related to summer minimumalbedo but showed no consistent relationship with summer temperature. Shrubtundra showed higher albedo than wetland and barren tundra in all four studyareas. These results suggest that a northwards shift of shrub tundra might notlead to a decrease in summer minimum albedo during the snow-free season whenreplacing wetland tundra. A fully integrative study is however needed to link resultsfrom satellite data with in situ observations across the Arctic to test the effect ofincreasing shrub cover on summer albedo in different tundra vegetation types.