Stipa Capensis Research Articles

Spatiotemporal Demographic Processes in Plant Populations: An Approach and a Case Study

The present paper suggests an approach combining theory and experiments to describe and analyze the effects of seed dispersal and seed dormancy on the population dynamics of annual plants. The approach is based on the identification of three potential sources of recruitment to plant populations: (1) local reproduction; (2) the soil seed bank; and (3) the net gain from dispersal. The quantitative relationships of the three sources determine the relative importance of dispersal and dormancy in population maintenance. Mathematical expressions for the different sources in the form of specific combinations (components) of demographic variables and parameters are derived from a dynamic model of an annual population in a spatially and temporally variable environment. An experimental procedure for quantifying the model components is described. This procedure was used to investigate the joint effects of dispersal and dormancy on the dynamics of populations of the desert annual Stipa capensis. The results confirm...

Suppression of Annuals by Artemisia Herba-Alba in the Negev Desert of Israel

SUMMARY In the Northern Negev (Israel) annual plants are more numerous on south-facing slopes dominated by Zygophyllum dumosum than on north-facing slopes dominated by Artemisia herba-alba. On the latter slopes annuals are fewer in the vicinity of A. herbaalba than elsewhere. In the year following experimental removal of Artemnisia plants the number of annuals increased, but remained smaller than on the south-facing slope. Unless there are differences in soil seed reserves, this suggests an inhibitory after-effect due to Artemisia. Experimental evidence is presented for the release from A. herba-alba shoots of volatile and water-soluble substances which strongly inhibit the germination of Helianthemum ledifolium and Stipa capensis. In Zygophyllum dumosum and cultivated tomato germination was less strongly inhibited, and in Medicago laciniata var. laciniata and var. brachyacantha not at all. No inhibition was exerted by Zygophyllum dumosum leaves. The inhibition of Stipa capensis and tomato by aqueous extracts of Artemisia shoots was to some degree reversible by short periods of leaching. The possible role of chemical inhibition of certain annuals in stands of A. herba-alba is discussed.