WATER AND TREE-UNDERSTORY INTERACTIONS: A NATURAL EXPERIMENT IN A SAVANNA WITH OAK WILT

Savanna trees influence water, light, and nutrient availability under their canopies, but the relative importance of these resources to understory plants is not well understood. In a three-year study in a Texas savanna, trees infected with the disease oak wilt were used in a natural experiment to isolate the effects of light and soil resources, particularly water, in oak–understory interactions. Herbaceous biomass and survival of transplanted Prosopis glandulosa (mesquite) seedlings were monitored in plots under healthy and symptomatic Quercus fusiformis (live oak) trees, and in open sites. Shade cloth maintained similar midday light levels in plots under symptomatic and healthy trees. Plant physiological attributes, soil parameters, and woody plant densities were also compared across habitats. Water availability was significantly lower near healthy trees than near symptomatic trees or in the open. Shade-cloth plots under symptomatic trees had over twice the herbaceous biomass of ambient-light plots under...

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