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Long-term consequences of a wildfire for leaf-litter breakdown in a Mediterranean stream

Abstract:

Wildfire frequency and intensity are expected to increase as a result of climate change, but few studies have assessed the effects of wildfires on stream ecosystem processes. The aim of our study was to examine the long-term responses of leaf-litter breakdown to wildfire in a Mediterranean stream. Riparian canopy cover was reduced by a fire, resulting in higher temperatures and light levels and reduced leaf-litter inputs in the stream 8 y after the fire. Benthic invertebrate communities recovered quickly after the fire, and the abundances of different functional feeding groups (FFGs), including shredders, were not different between streams affected and unaffected by the fire after α2 postfire years. We compared microbially mediated (fine-mesh bags) and total breakdown rates (coarse-mesh bags) of Populus alba leaf litter incubated in the stream affected by the wildfire and a neighboring control stream. Microbial and total leaf-litter breakdown were faster in the stream affected by fire. Faster microbially induced litter decomposition in the fire-affected stream could be attributed almost entirely to increased water temperatures, but total litter breakdown rates were enhanced by higher shredder abundance in coarse-mesh leaf bags in the fire-affected than control stream. Lower leaf-litter inputs in the fireaffected than in the control stream probably led to lower benthic organic matter levels, leading to increased shredder aggregation in leaf packs, thereby accelerating leaf breakdown rates. Our study indicates that past wildfires can modify key ecosystem processes, such as leaf decomposition, in the long term in Mediterranean streams.