Patterns of Primary Succession on Granite Outcrop Surfaces

Abstract

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.

Floristics, structure and soil of insular vegetation in four quartzite-sandstone outcrops of "Chapada Diamantina", Northeast Brazil

“…Severe environmental conditions, such as soil scarcity and nutrient deficiency, high daily temperature oscillations and intense irradiation restrict the occupation of the exposed rock by plants (Shure & Ragsdale 1977, Burrows 1990, Ware 1990, although these unfavorable conditions are somewhat ameliorated when the vegetation is denser (Daubenmire 1968). These plant aggregations surrounded by rock surfaces are called "soil mat communities" (Hambler 1964), "island communities" (Burbanck & Platt 1964, McCormick et al 1974, Shure & Ragsdale 1977,…”

Ilhas de vegetação em afloramentos de quartzito-arenito no Morro do Pai Inácio, Chapada Diamantina, Bahia, Brasil

“…Ilhas de plantas agrupadas em áreas pequenas e bem delimitadas pelo substrato rochoso de granitognaisse foram bastante estudadas na África e nos Estados Unidos, envolvendo enfoques variados em ecologia, como descrição estrutural e aspectos funcionais e temporais relacionados à sucessão primária (Weaver & Clements 1938;Burbanck & Platt 1964;Hambler 1964;McCormick et al 1974;Shure & Ragsdale 1977;Porembski et al 1995). Mesmo situadas em regiões distintas, essas ilhas de vegetação sobre rocha apresentam similaridades fisionômicas, apesar da distinção regional na composição de espécies de plantas (Porembski et al 1994;Seine et al 2000).…”

Reproductive phenology, pollination and seed dispersal syndromes on sandstone outcrop vegetation in the "Chapada Diamantina", northeastern Brazil: population and community analyses

“…special communities completely surrounded by rock surfaces are called "soil mat communities" in Africa (Hambler 1964), "island communities" in the United States (Burbanck & Platt 1964, McCormick et al 1974, Shure & Ragsdale 1977, and "soil islands" in Brazil (Meirelles 1996). Some of the highest peaks in northeastern Brazil are found in the Chapada Diamantina Mountain Range.…”