Disturbance, Seed Banks and Vegetation Dynamics of Desert Annuals
Investigators (most current known information)
Every rainy spring, annual plant communities in patchy semiarid shrubland are recruited from seeds that were: 1) produced the year before in the same patch, or 2) outside the patch, or 3) were lying dormant on or in the soil. This study examines the contribution of each of these seed sources (local, external, or residual) to community density, species richness, and species composition. Variation in the dependence of plant communities on these seed sources determines how they respond to changes in landscape structure by land use and management.
On a south-facing slope in Sayeret Shaked ILTER in the northern Negev of Israel, six groups-of-four plots of 1 x 2 m were delineated in the flat crusted intershrub matrix in 1998. The plot was bordered on the upper side and the long sides with a 5-cm high PVC wall. In the lower 30 cm, a 20-cm deep pit was dug, creating a plot with an undisturbed matrix and a soil pit without crust, which captures runoff generated on the crust. In one plot in each of the six groups local seed production was prevented by removal of the vegetation. In another six, vegetation was removed and the lower 30 cm of the matrix, and the pit was covered with a cotton sheet, canceling the external seed source as well. The third treatment was removal of vegetation and top 1 cm soil (of the pit), canceling both the local and the residual seed sources there. One plot per group was an unmanipulated control.
The plant community was sampled in 2002 in the lower 30 x 100 cm matrix and the entire 30 x 100 cm pit, by identifying species and counting individual plants. The results show that plant density on the matrix decreased by 50% in communities without local seed production, while species richness did not vary much around 10 species per patch. In the pits local seed production was unimportant. Residual seeds determined two-thirds of the density, while cancelling the external source decreased it by ca. 30%. Species richness varied little around 12 per patch.
Articles in Journals
Boeken, B. and M. Shachak. 2005. "Linking community and ecosystem processesthe role of minor species." Ecosystems (in press)
Boeken, B and M. Shachak. 2005. "Response diversity, community organization and resilience to drought of a semi-arid annual plant assemblage." Journal of Ecology (submitted).