Document: BER-3-40-2

Facilitation of dominant by subordinate species in herbaceous desert plant communities.

BOEKEN, B.* and M.SHACHAK

Ben-Gurion University of the Negev, Israel 84990 ¹

Abstract:
We studied the role of local seed production and seed rain in determining plant density, biomass and species richness of annual plant communities by selective and total vegetation removal in small-scale inter-shrub patches of a semi-arid shrubland. In one field experiment the entire annual vegetation was removed from eight 1m x 1m plots for 6 years (1993-98). In another only the most dominant species, the annual grass Stipa capensis, was removed from ten 60 cm x 60 cm plots for 3 years (1996-98). All plants were identified and counted in spring of each year. Vegetation removal caused a decrease in plant density and biomass, due to the decline of the two dominant annual grass species S.capensis and Bromus fasciculatus. Mean densities of other species and species number were not affected. Selective S. capensis removal had no effect on density or species number, nor on its own density. Vegetation removal frequency did not affect other species either, but caused progressively lower densities and biomass of the two dominants. We conclude that in spite of removal of local seed production, seeds of the dominant and the subordinate species arrive, but that those of S.capensis can only establish in the presence of the subordinates. The facilitation overcomes the inability of S. capensis seeds to penetrate into the dense soil crust if there are no obstacles providing leverage.

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This abstract is being presented at: 1:45 PM in session:
Oral Session #33: Plant Demography.