SPECIES-AREA RELATIONSHIP DURING PRIMARY SUCCESSION IN GRANITE OUTCROP PLANT-COMMUNITIES

The species-area relationship was investigated in a primary successional sere on a SE US granite outcrop. There, plant communities occupy soil-filled depressions separated from one another by areas of bare rock. They have been termed "island communities'. Soil depth and area increase as succession proceeds from Sedum smallii, to lichen-annual, to annual-perennial, and to herb-shrub-tree stages. Although plant species richness is significantly and positively correlated with island area in the system studied, the relationship between species richness and island maximum soil depth is stronger. However, island maximum soil depth and area are significantly and positively correlated. The exponential function describes the species-area relationship better than the transformed power function. Within successional stage, species richness shows no significant relationship with area or depth, except for late-successional island communities. Processes related to community successional development may explain the species-area relationship that exists when islands of all stages are considered, but mechanisms related to equilibrium between extinction and immigration may be responsible for the species-area relationship for late-successional island communities. -from Author