Characterization of Site-Specific Vegetation Activity in Alaskan Wet and Dry Tundra as Related to Climate and Soil State DATA

<p>We present discrete (2-hour resolution) multi-year (2008 &ndash; 2017) <em>in situ </em>measurements of seasonal vegetation growth and soil biophysical properties from two sites on Alaska&rsquo;s North Slope, USA, representing dry and wet sedge tundra. We examine measurements of vertical active soil layer temperature and soil moisture profiles (freeze/thaw status), woody shrub vegetation physiological activity, and meteorological site data to assess interrelationships within (and between) these two study sites.</p> <p>Vegetation phenophases (cold de-hardening start, physiological function start, stem growth start, stem growth end, physiological function end, cold hardening completion) were found to have greater inter-annual Day-Of-Year (DOY) occurrence variability at the dry site compared to the wet site. At the dry site, vegetation activity begins on average ~ 7 days earlier and ends ~ 11 days earlier. The mean active stem growth window lasts ~ 54 days for the dry site and ~51 days for the wet site. Vegetation, in both tundra environments, began cold de-hardening functions (warm season prep) prior to atmospheric temperatures warming above 0&deg;C. Similar results were found related to the critical soil freeze/thaw/transition dates; the dry site had a DOY phenophase occurrence range that was 8 days larger than that of the wet site. A longer continuous summer thaw period was captured at the wet site by ~ 26 days throughout the active layer. In addition, the dry site was measured to have longer spring and fall soil isothermal conditions than the wet site by ~ 9 and 5 days throughout the active layer. These results show that the dry site&rsquo;s willow shrub vegetation physiology and soil condition phenology is more variable than the wet site.</p> <p>Alongside the <em>in situ</em> data, a remote sensing product from NASA&rsquo;s MEaSUREs program was utilized; our research indicates that the AMSR derived satellite product is more precise over the wet tundra site with critical date alignment between remote sensing observations and <em>in situ</em> measurements ranging from ~ 4 to 11 days. Furthermore, the AMSR product was shown to preemptively estimate land surface condition change during the spring transition for both tundra types while lagging during the fall transition and freeze-up periods.</p>