Description

Longleaf pine savannas are fire-dependent ecosystems typically characterized by relatively nutrient-poor soils. It is generally agreed that repeated fires reduce competition and maintain plant species diversity in these systems. One documented effect of fire is the reduction of aboveground competition through the destruction of aboveground parts of plants and the combustion of associated litter. In addition to fire, low soil fertility is thought to maintain species diversity in pine savannas. Two alternative hypotheses are offered to explain species coexistence in nutrient-poor soils. 1) Plants avoid competition for nutrients with one another by occupying different niches at fine spatial scales, 2) Slow growth and low nutrient demand limit competition. Recent investigations of competition between carnivorous pitcher plants and their neighbors have shown that, in years without fire, depriving pitcher plants of prey does not reduce their competitive ability. Apparently, low soil nutrient demand and slow growth obviate intense competition between pitcher plants and their neighbors. However, nutrient demand (measured as investment in carnivory) is a plastic trait, which increases significantly following fires. Because most fires in pine savannas cause little mortality and tend not to damage belowground parts of plants, increases in nutrient demand following fire could lead to increased belowground competition for nutrients. Hence, complementary nutrient use by carnivorous and non-carnivorous plants after fires could contribute to coexestence. I argue that studies that attempt to test altermative hypotheses about competitive mechanisms in longleaf pine savannas should consider the effect of fire-regulated plasticity in nutrient demand. © by the Ecological Society of America. Abstract reproduced by permission.