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  • Thumbnail for Fire History Effects on Organic Matter Processing from Hillslopes to Streams
    Fire History Effects on Organic Matter Processing from Hillslopes to Streams by Gilbertson, Asheton

    Climate change impacts temperature and precipitation regimes which can shift species composition and induce state changes. Disturbance events, which alter the productive capacity of ecosystems, may also shift pre-disturbance stable states to entirely new, alternative stable states. Under scenarios of increased frequency and intensity of disturbances predicted with climate change, state shifts are likely to become more common. In the Intermountain West, interactions between climate change and severe wildfires may decrease forest resilience through forest ecosystem conversion to different tree species assemblages, shrubland or grassland states. Our findings support the notion that current shifts from forest to non-forested vegetation may be underway and that these changes are likely expedited by wildfire disturbance. Results indicate that severe wildfire has markedly altered soil OM pools such that burned sites are not only storing significantly less SOM (burned soils contained 77% less C than reference soils) but retaining a significantly smaller fraction of SOM than unburned sites (burned soils retain 4% less DOC, 3.4% less TDN and 3.7% less DON than unburned soils export to the subsurface). Transformation of flow paths in burned landscapes also had cascading effects on nutrient concentrations in streams: DOC and DON concentrations were 50% to 80% higher in burned streams relative to unburned streams. This study shows that even fifteen years postfire, C accumulation, sequestration and transport remain altered, providing further evidence that Ponderosa pine forests in the Intermountain West may transform into a decadal‐scale C source under a more frequent and severe disturbance regime.