Patterns of Primary Succession on Granite Outcrop Surfaces

Shure, Donald J.; Ragsdale, Harvey L.

Patterns of Primary Succession on Granite Outcrop Surfaces

1977

Shure, Donald J. | Ragsdale, Harvey L.

The patterns of primary succession were studied in soil—island communities on a granite outcrop in Georgia. The island communities increase in area and depth over time and the soil becomes more organic. The strong moisture and temperature fluctuations that occur in shallow pioneer soils are significantly reduced in the later stages. Plant biomass and vertical stratification increase throughout succession as larger plant species invade the deeper communities. A small winter annual is the dominant pioneer species. Lichens, annuals, and eventually perennial species invade as succession progresses. Interspecific competition for moisture and nutrients regulates plant species composition at successive stages. Macroarthropod populations increase in density, biomass, and diversity throughout succession. The few soil microarthropod species that occur in the pioneer stages often exhibit rapid density oscillations in the shallow substrates. The deeper and more environmentally constant substrate of later stages contains a greater variety of microarthropods. Biotic diversity generally increases during primary succession on the outcrops. Plant diversity peaks at intermediate stages while microarthropod and macroarthropod diversity increase from pioneer through later stages. The strong physical factors on the outcrops determine the rate and extent of community development in particular soil—islands. However, as the many soil—islands undergo succession they converge in community characteristics such as total density, biomass, and diversity.

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