Altered water and nitrogen input shifts succession in a southern California coastal sage community.

摘要: Vegetation-type conversions between grasslands and shrublands have occurred worldwide in semiarid regions over the last 150 years. Areas once covered by drought-deciduous shrubs Southern California (coastal sage scrub) are converting to dominated nonnative species. Increasing fire frequency, drought, nitrogen deposition all been hypothesized as causes of this conversion, though there is little direct evidence. We constructed rain-out shelters a coastal scrub community following wildfire, manipulated water input split-plot design, collected annual data on composition for four While shrub cover increased through time plots during postfire succession, both drought significantly slowed recovery. Four years after fire, average native ranged from 80% addition, ambient-nitrogen 20% reduction, addition plots. Nonnative grass was high remained reduction third spring before decreasing fourth year study. Adding decreased plants grasses, but also growth one crown-sprouting Our results suggest that extreme succession may slow or alter possibly facilitating vegetation-type conversion grassland. Nitrogen and, when combined with cover. Fire, atmospheric N widespread aspects environmental change occur simultaneously system. imply these drivers reinforce each other, leading continued decline