| Summary: | Warming in recent decades has triggered shrub expansion in arctic and alpine tundra, which is transforming these temperature-limited ecosystems and altering carbon and nutrient cycles, fire regimes, permafrost stability, land-surface climate-feedbacks, and wildlife habitat. Where and when Arctic shrub expansion happens in the future will depend in part on how different shrub communities respond to warming air temperatures. Here, we analyze a shrub ring-width network of 18 sites consisting of Salix spp. and Alnus viridis growing across the North Slope of Alaska (68-71 North; 164-149 West) to assess shrub temperature sensitivity and compare radial growth patterns with satellite NDVI (normalized difference vegetation index) data since 1982. All shrub sites and species shared a common year-to-year growth variability despite site differences and had a positive response, ~67% of which were significant (P less than 0.05), to daily maximum air temperatures (Tmax) from ca. May 31 (i.e. Tmax ~6 Celsius (C)) to early July (i.e. Tmax ~12 C). Thus, the month of June had the highest shrub growth-temperature sensitivity and this period coincides with the seasonal increase in temperature and an green-up of tundra indicated by both field observations and the seasonal cycle of NDVI (~photosynthetic activity). Nearly all of the sampled shrubs (98%) initiated their growth after 1960, with 74% initiated since 1980. This post-1980 shrub-recruitment pulse coincided with ~2 C warmer June temperatures compared to prior periods and positive trends in shrub basal area increments (BAI) and peak summer NDVI. Significant correlations between shrub growth and peak summer NDVI indicate these radial growth patterns in shrubs reflect a broader trend of enhanced tundra productivity across the North Slope of Alaska. This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Alaska, United States Of America. The time period coverage is from -27 to -60 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data.
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