Rebecca A. Lybrand

A net ecosystem carbon budget for snow dominated forested headwater catchments: linking water and carbon fluxes to critical zone carbon storage

Climate-driven changes in carbon (C) cycling of forested ecosystems have the potential to alter long-term C sequestration and the global C balance. Prior studies have shown that C uptake and partitioning in response to hydrologic variation are system specific, suggesting that a comprehensive assessment is required for distinct ecosystems. Many sub-humid montane forest ecosystems in the US are projected to experience increased water limitation over the next decades and existing water-limited forests can be used as a model for how changes in the hydrologic cycle will impact such ecosystems more broadly. Toward that goal we monitored precipitation, net ecosystem exchange and lateral soil and stream C fluxes in three semi-arid to sub-humid montane forest catchments for several years (WY 2009–2013) to investigate how the amount and timing of water delivery affect C stores and fluxes. The key control on aqueous and gaseous C fluxes was the distribution of water between winter and summer precipitation, affecting ecosystem C uptake versus heterotrophic respiration. We furthermore assessed C stores in soil and above- and below-ground biomass to assess how spatial patterns in water availability influence C stores. Topographically-driven patterns in catchment wetness correlated with modeled soil C stores, reflecting both long-term trends in local C uptake as well as lateral redistribution of C leached from upslope organic soil horizons to convergent landscape positions. The results suggest that changes in the seasonality of precipitation from winter snow to summer rain will influence both the amount and the spatial distribution of soil C stores.

Soils of the Western Range and Irrigated Land Resource Region: LRR D

The arid and semiarid ecosystems of the Western Range and Irrigated Region occupy large areas across the states of Oregon, California, Idaho, Nevada, Arizona, Utah, New Mexico, Wyoming, Colorado, and Texas. These areas are largely comprised of desert and semi-desert ecosystems located on broad plateaus, plains, basins, and isolated mountain ranges providing areas of forested habitat. The ecosystems in this region are predominantly dominated by shrubs, grasses, and scattered trees in the low lying areas, with areas of forest in the cooler, wetter mountain ranges. Much of the low lying land in this region is used for grazing with areas of irrigated agricultural production where water is available and soils are suitable. The soils in this region are dominantly Aridisols , Entisols, and Mollisols. The dominant suborders include Argids and Calcids on alluvial fans, plains, and basins ; Orthents and Fluvents on alluvial fans, plains, plateaus, and valleys; and Xerolls and Ustolls on mountain slopes. The soils in this area are central to sustainable ecosystem management and function, providing critical ecosystem services such as watershed and groundwater recharge, carbon sequestration , and maintenance of plant and animal diversity over a large area of the Western US.