Autogenic Succession in a Subtropical Savanna: Conversion of Grassland to Thorn Woodland
Archer S, Scifres C, Bassham CR. 1988. Autogenic Succession in a Subtropical Savanna: Conversion of Grassland to Thorn Woodland. Ecological Monographs. 58(2):111-127
Dense thorn woodlands occupy what are thought to have been grasslands and savannas prior to settlement of the Rio Grande Plains of Texas. However, the tenet that grasslands have been converted to shrublands and woodlands in a recent history in controversial and based largely upon conflicting historical accounts. Our objective was to determine how the presumed physiognomic conversion from grassland or savanna to woodlands might have occurred. Some upland landscapes are dominated by closed-canopy woodlands in southern Texas, whereas others have a two-phase pattern of discrete shrub clusters scattered through a grassland. More mesic sties are dominated by closed-canopy woodlands. We hypothesized the two-phase landscapes represented an intermediate stage in the conversion of grassland to woodland. As new shrub clusters were initiated and existing clusters expanded and coalesced, a gradual shift from grassland to savanna to woodland would occur. Two address this hypothesis, we inventoried herbaceous interspaces for woody colonizers, quantified the composition and distribution of shrub clusters on upland sites, and compared the structure of clusters to that of adjacent, more mesic areas with continuous woody plant cover. To assess the physiognomic stability of the two-phase landscapes, cluster size, density, and cover were quantifies for 1941, 1960, and 1983 from aerial photographs.
- Type
- Journal Article
- Authors
- Archer, Steve; Scifres, Charles; Bassham, C.
- Units
- SODN
- Keywords
- DECORANA, detrended correspndence analysis, Diversity, facilitation, Grazing, Mesquite, mosaics, Patterns, Prosopis glanulosa, Rio Grande Plains, size class distribution, species-area curve, Tamaulipan Biotic Province, Texas