Print PageCarbon budget analyses suggest montane ecosystems as a potentially large, but highly uncertain, portion of the North American carbon sink. While eddy covariance measurements of net ecosystem exchange of CO2 provide insight into the carbon-sink potential of montane ecosystems, compartmentalization of ecosystem respiration (Reco) into aboveground and belowground soil (Rsoil) fluxes is often difficult. This is particularly true in areas of non-homogenous topography and variable soil microclimate, such as those found in complex terrain. Understanding the relative contribution of Rsoil to Reco and the spatio-temporal responses of Rsoil to varying temperatures and moistures will inform predictions of Rsoil in future climate scenarios. This study was conducted along a pair of converging drainages within a montane mixed-conifer forest located below an eddy covariance tower in the Santa Catalina Mountains of southern Arizona. Rsoil was quantified at fixed points along transects running perpendicular to each drainage such that the influence of upslope accumulated area and distance from the drainage could be interpreted. Measurements were made across these spatially distributed points nearly bi-weekly from prior to the monsoon until snow accumulated and again after periods of snow melt. Soil moisture, soil temperature, air temperature, and litter-layer thickness were quantified along with soil respiration and evaporation.
Results/Conclusions
We were able to quantify the relative influence of topographic and environmental drivers of seasonal and cumulative patterns of Rsoil. Rsoil was significantly influenced by the onset of our summer monsoon in that average Rsoil stimulated by 118%. While additional rains increased soil moisture by 58%, average Rsoil remained unchanged. Rates decreased throughout the post-monsoon following patterns of decline in available water. With regard to topography, aspect influenced patterns of Rsoil though distance to drainage did not. The influence of aspect was seasonally important, in that it was a major driver in the early monsoon but less so under moist summer conditions. Together, these results illustrate the influence of Rsoil to water pulse events at the initiation of the monsoon season, to topography under wet conditions, and to low soil temperatures during melt. Further spatial analysis will allow us to calculate the influence of upslope accumulated area, which is a measure of the concentrating water resources due to topography, on point measures of Rsoil. In so doing, we will link the influence of hydrologic forces to ecologically relevant processes in this complex terrain setting.
