Soil carbon dynamics in montane meadows of the Sierra Nevada and southern Cascade mountain ranges

Abstract

Soils are important drivers of the terrestrial carbon cycle and may present greater opportunities for C sequestration than aboveground ecosystem components. Anthropogenic disturbance and restoration can impact the direction and magnitude of net ecosystem C fluxes, potentially mitigating or amplifying rates of climate change. Changes in ecosystems with large soil C stocks, including montane meadows, may have outsized impacts on terrestrial C cycles. My dissertation quantifies rates and patterns of soil C flux in pristine, degraded, and restored montane meadows throughout the Sierra Nevada and southern Cascade mountain ranges. My results suggest that montane meadows can be large net C sinks (577.6 ± 250.5 g C m-2 y-1), sequestering as much C as evergreen tropical forests per unit land area, or sources of C to the atmosphere (-391.6 ± 154.2 g Cm-2 y-1). The direction and magnitude of the net C flux in meadows appears to be driven by belowground C inputs rather than outputs and associated with levels of disturbance. Modeled rates of net ecosystem C flux based on high resolution field measurements and remote sensing data revealed that, region-wide, meadows were a net source of 408 Gg C between August 2015 and July 2016. However, restoration of meadow floodplain hydrology appears to stem the loss of C from degraded meadows and increase rates of soil C sequestration. Across a 22-y meadow restoration chronosequence, soil C stocks increased at a rate of 256 g C m-2 y-1 and soil C concentration increased by 0.3% per year. My dissertation provides estimates of previously unquantified ecosystem-level C fluxes in montane meadows and underscores that, in their current condition, many meadows throughout the region may be large net sources of C to the atmosphere. However, I also demonstrate the potential of relatively undisturbed or restored montane meadows to sequester and store large amounts of C. My results suggest that effective C management in meadows will involve identifying and conserving meadows that are net C sinks along with efforts designed to restore floodplain hydrology in degraded meadows.