As the climate warms, high elevation ecosystems will be exposed to novel conditions as the snow-free period extends further into the spring and fall. Alpine and sub-alpine systems rely on snowmelt for moisture through the summer months. With snowmelt beginning earlier, these systems will be exposed to dryer, warmer conditions for much of the summer. This ongoing project is focused on the influence of soil moisture, soil temperature, air temperature, and cover vegetation on soil respiration. In June of 2015, 12 sites were established in Rocky Mountain National Park, Colorado. Sites were distributed across 3 plots with distinct vegetation and soil regimes: 1) Conifer forest at the upper limit of the tree line 2) Tundra characterized by shallow soil and minimal vegetation consisting of herbs and lichens 3) Tundra characterized by organic-rich, deep soil and abundant vegetation consisting of grasses and sedges. Soil respiration, soil temperature, soil moisture, and air temperature were measured weekly throughout the snow-free period of 2015, 2016, and 2017 (expected).
Soil moisture and air temperature were negatively correlated with soil respiration across the three vegetation types. The interactions of soil moisture * air temperature and soil moisture * cover type were also significant. Respiration rates were significantly different in the three cover types and was highest in the forest (maximum 9.8 µmol/ m2/sec) and lower in the two tundra sites (maximum 4.9 µmol/ m2/sec). From these results, it appears that soil moisture and air temperature are both influencing soil respiration. In this system, these variables generally have an inverse relationship: when soil moisture is high (due to snowmelt in the spring), air temperature is low and when soil moisture is low (in late summer), air temperature is high. If soil moisture and air temperature both influence the respiration rate, the inverse relationship between soil moisture and air temperature could explain the negative correlation between these variables and soil respiration. Future work will focus on soil chemistry to determine the role (if any), soil nutrient availability and pH have on soil respiration in these high elevation systems.