PARENT SESSION
Oral Session #19: Plant Competition. Presiding: N. Slade.
Monday, August 6, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.
Effect of perennial bunchgrass density and soil rock fragment content on Prosopis velutina size and production.
Thomas, Leigh1, Weltzin, Jake1, 1
ABSTRACT- In semi-arid regions, spatial and temporal patterns of soil moisture dictate plant distribution and abundance, especially in ecotonal communities such as savannas. Within savannas, woody plant seedlings and bunchgrasses often compete for soil moisture, which may be affected by the abundance of rock fragments in the soil profile. Our goal was to evaluate the response of seedlings of the arborescent legume Prosopis velutina along gradients of (1) density of the C4 bunchgrass Eragrostis lehmanniana, and (2) soil rock fragment content. Four levels of grass (thinned to 0, 110, 220, and 440 plants/m2 at experiment initiation) were combined with three levels of rock fragment content (0, 15, and 30% by volume, achieved by mixing known volumes of gravel with silty loam soil) in a completely randomized design. Dependent variables included shoot, root, and total mass, shoot height, leaf number, and root:shoot ratios for P. velutina seedlings, and shoot mass for E. lehmanniana. All P. velutina mass and size response variables were inversely related to E. lehmanniana densities (P < 0.0001). P. velutina mass and size were greatest at intermediate soil rock fragment contents (P < 0.0001). Results indicate that increasing densities of E. lehmanniana adversely affect size and production of P. velutina, and suggest that intermediate quantities of rock fragments may facilitate percolation of soil moisture to depths accessible only by roots of the woody plant seedlings.
KEY WORDS: Prosopis velutina, Eragrostis lehmanniana, semi-arid savanna