Carbon Cycling and Storage in Mountainous Terrain With Varied Disturbance and Forest Management

Forest ecosystems interact with atmospheric CO2 concentrations by sequestering and storing CO2 in biomass. In the western US, a large proportion of C storage occurs at high elevations in mountainous terrain. Because these forest ecosystems are heterogeneous in terms of climate, topography, and management, scaling carbon storage and flux estimates to landscape and regional scales is challenging. The goals of this research were to provide a better understanding of forest carbon dynamics and their response to management activities in mountainous terrain. The specific objectives were to: 1) develop an isotope tracer method to measure tree scale carbon flux, 2) describe the topographic variation in carbon flux in mountainous terrain and 3) determine stand scale controls over carbon storage and flux in terms of disturbance, forest management, and topographic position in mountainous terrain.;The tree level isotope tracer method was developed to study the fate and transformation of carbon as it is assimilated in the tree canopy and translocated into the phloem, soil matrix and soil microorganisms. This experiment developed a new method of 13C-labeling by injecting 13C-carbonate dissolved in water into the xylem of an individual tree and traced the movement of the assimilated 13C label with measurements of the isotopic composition of individual tree C pools prior to labeling and up to 3 weeks post labeling. This will allow us to quantify the rates of C transport through the plant-soil-atmosphere continuum and to apply experimental manipulations to study the biophysical controls over tree carbon dynamics and their response to disturbance.;Plot and stand level carbon storage and sequestration rates were measured on treatments with 1) variable harvest intensity in a temperate conifer forest in Northern Idaho, and 2) treatments with variable post-fire management activities in a mixed conifer forest in the Sierra Nevada Mountains. Findings of management influences on C storage and sequestration were: nonlinear patterns in carbon flux in mountainous terrain, (2) reduced C storage and sequestration in clear-cut and post-fire salvage logged stands. These results support the need to account for topographic position and forest management in the next generation of ecosystem- and global-scale C models. This research provides management options to balance efforts to manage forests for carbon sequestration, forest resources, and fire hazard reduction.