Influences of frequent cool-season burning across a soil moisture gradient on oak community structure in longleaf pine ecosystems.

摘要

Fire and soil moisture gradients are thought to influence oak community structure in longleaf pine (Pinus palustris) woodlands. To explore these influences, oak density and species composition were measured within a longleaf pine/wiregrass (Aristidastricta) dominated landscape subjected to frequent (every 2-4 yr) cool-season prescribed burning for 70 yr. At 64 locations within the Joseph W. Jones Ecological Research Center in southern Georgia (USA), oak (Quercus spp.) trees, saplings and regeneration (seedlings plus sprouts) were counted in nested plots, and 20 additional measurements were taken to assess physical and chemical properties of soils, disturbance, density of other vegetation and topography. Principal components analysis of soil datarevealed a soil moisture and soil chemistry gradient. Trees and saplings were sparse (mean of 37 and 81/ha) and most common in dry and dry-mesic sites, while regeneration was abundant (mean of 110 100 stems/ha) and well-distributed across the soil moisture gradient. Fifty percent or more (depending on vegetation stratum analysed) of the cumulative species-environment relationship was accounted for in the first two axes of a canonical correspondence analysis with axes representing gradients in soil moisture and several chemical and physical properties including mineralizable N, extractable Ca and Mg and soil texture. Three oak species were concentrated in the dry end of the soil moisture gradient, 4 in the moist end, and one was common across much of the gradient. Species distributions probably reflect physiological tolerances of soil moisture extremes plus variation in fire regime caused by differences in soil moisture. Forest fragmentation and prescribed cool season burning may have increased oak densities in this landscape. If so, a change in fire regimes may be necessary to mimic natural disturbance patterns better.