Primary Succession on Granite Outcrops in Southwestern Oklahoma

Abstract

UNO, G. E. AND S. L. COLLINS (Dept. Bot. and Micro., Univ. Oklahoma, Norman, OK 73019). Primary succession on granite outcrops in southwestern Oklahoma. Bull. Torrey Bot. Club 114: 387-392. 1987.-Species presence was recorded in 90 islands of soil on granite outcrops in southwestern Oklahoma. Islands ranged in size from 0.002 to 22.4 m2 (x = 1.17 im2). Species cover was estimated in 795 10 x 10 cm quadrats located along transects in 11 of the largest islands. A total of 37 plant species was recorded in 48 of the 90 islands, the remaining islands contained soil but no plants. Soil samples were collected from 18 of the unvegetated islands. From these samples, only four seedlings grew, suggesting that seed pool sizes are extremely small in bare islands. Excluding unvegetated islands, species richness was positively correlated with island size and soil depth. Cluster analysis of the island data produced four community types which differed significantly in species richness and soil depth. Based on cover, the most common species were Selaginella peruviana (47%), Sedum nuttalianum (25%), Bouteloua hirsuta (18%), and Plantago wrightiana (10%). Association analysis of the common species indicated a successional sequence that begins with islands dominated by Selaginella or Sedum on shallow soils. As soil depth increases, species richness increases and islands become dominated by perennial grasses characteristic of the surrounding mixed-grass prairie.