Causes and consequences of annual variation in disturbance in salt marsh plant communities

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We examined the controls on Spartina alterniflora annual net primary production (ANPP) in eight marshes in Georgia. We examined the importance of three types of disturbance (wrack, wildlife and slump disturbance) and six abiotic drivers (site location, elevation, sea level, river discharge, precipitation and max temperature) on ANPP, examining effects in creekbank and midmarsh zones separately. We found S.alterniflora in creekbank was commonly disturbed by wrack and slump, while S.alterniflora in midmarsh was commonly disturbed by wildlife. For the creekbank, slumping did not affect biomass until the plot was totally lost. Wrack disturbance reduced biomass by about 50 %. For the midmarsh, wrack is not an important disturbance, but wildlife disturbance reduced biomass by about 75%. In addition, several abiotic variables (river discharge, max temperature, sea level and precipitation) affected year to year variation in biomass.