Paleoecological data indicate that Arctic landscapes in Alaska have been far from static during the Holocene. For example, the relative dominance of spruce and deciduous forests varies with temperature influences on fire frequency. In the modern and future warming Arctic, the degree to which Holocene conditions are analogous depends on changes in interactions among several climate-driven variables, including active layer depth in permafrost regions, fire frequency, and post-fire ecohydrology. Modern climate-fire relationships indicate that fire is responsive to both precipitation and temperature, and is likely to increase in area and frequency in the 21st century. Here we propose an integrated mechanism of ecological drought in boreal systems and present observations from local to regional scales supporting further inquiry into ecological dorught. In permafrost or discontinuous permafrost regions, increases in the depth of the summer active layer increase the depth of possible root zones, but also the depth of preferential flow paths of melt or precipitation, so the consequences for vegetation depend on soil permeability and field capacity. Changes in the duration of flammability for surface vegetation or peat increase the potential severity of fires, which in turn increases temperature of the active layer after fire more than expected with increased air temperature alone, so post-fire recovery of permafrost is less likely. The regeneration of the historical forest type – or the shift to a different vegetation – is dependent on post-fire physical and hydrologic parameters, which will change with climate change.
Results/Conclusions
Comparing air temperature, surface temperature, soil moisture, snowpack, and streamflow data for two years from a small boreal watershed that was partially burned in 2003 allowed us to explore a range of regeneration microclimates in high-severity versus unburned boreal forest. We observed within-watershed variability in the timing of snowmelt and the range of maximum and minimum temperatures, with largest variation during and shortly after snowmelt. We also present sap flux responses from black spruce in the watershed across a gradient of fire severity and hill slope position, with both hill slope position and fire severity affecting sap flux. Regionally, time since fire is expected to decrease over much of the landscape, and the proportion of the landscape in deciduous vegetation to increase.