Knowledge Bank

In Arctic and Sub-Arctic regions, the existence of permafrost, a layer of soil below the earth’s surface that stays below the freezing point of 0°C for two consecutive years, depends largely on air surface temperatures. Therefore, with the occurrence of climate warming, permafrost extent and depth is changing throughout vulnerable regions located within and near the Arctic. With these regions heating up at more than twice the speed of the global average, it is becoming increasingly important to understand the dynamics of permafrost thaw and freeze cycles, as active layer thickness (ALT), which is defined as the height of the subsurface layer that freezes and thaws above the permafrost on an annual basis, affects infrastructure, methane, and carbon emissions. The vegetation that exists in permafrost regions is expected to play a large role in the progression of permafrost degradation, as plant hydraulics interact with the soil moisture, affecting characteristics such as thermal conductivity. Here, we analyze these predicted interactions between plant hydraulics and permafrost depth by coupling the GIPL soil temperature model and a plant hydraulics model. Using a robust soil, atmospheric, and plant hydraulic dataset collected at a site near Fairbanks, Alaska, independent and coupled real-world scenarios were tested. With plant hydraulics, we find that frozen soil depth has an impact on plant water stress. For frozen soil depth, we find that soil moisture impacts soil temperatures. However, sensitivity tests suggest that the thermo-physical properties of organic soils are not accurately captured by the GIPL model without further calibration.