The Patagonian steppe is a temperate semiarid ecosystem composed by shrub and tussock grasses. Total cover in the community is 50%. Grasses and shrubs are spatially organized in a two-phase mosaic. High-cover patches are formed by grasses and shrubs. Low-

AGUIAR,M.R.; WIEGAND, T.; CIPRIOTTI, P.A.; PARUELO, J.M.

Freising, Alemania

Congreso; International Asociation Vegetation Science Symposium; 2001

IAVS

The Patagonian steppe is a temperate semiarid ecosystem composed by shrub and tussock grasses. Total cover in the community is 50%. Grasses and shrubs are spatially organized in a two-phase mosaic. High-cover patches are formed by grasses and shrubs. Low-cover patches are formed by scattered tussock grasses. To study the temporal and spatial patterns of the species and the processes that maintain this two-phase mosaic we developed a simulation model that simulates soil seed bank, seed dispersal, establishment, growth, reproduction, and mortality of shrubs and grasses. The model simulates all the processes in cells 400cm² in area arranged in a grid of 100 x 100 cells in a monthly time step. Temporal plant dynamics result from seed dispersal, life history process of the species, and interaction among plants (competition and facilitation) and water availability in the different soil layers. Spatial dynamics among cells occurs via seed dispersal and rules that allow the growth of shrubs in grass-dominated cells but forbid the growth of grasses in shrub- dominated cells. Simulations highlight the importance of seed dispersal in controlling population distribution and dynamics.