Anthropogenic disturbances to shrubs as ecosystem engineers and their effects on biodiversity

The semiarid ecosystems of the Negev have been subjected to anthropogenic disturbances for thousands of years. This includes livestock browsing and cutting shrubs for firewood. It has been suggested that shrubs are ecosystem engineers that modulate the landscape and resources available for other organisms. We tested the effects of clear cutting and browsing, on shrubs. We measured the effects of shrub cutting and browsing on the diversity of annual plants, spiders and soil dwelling arthropods. We found that the organisms respond to three distinct patch types in the landscape: shrub, biogenic crust and the edge between the shrub and crust. In the shrub patch there is a relatively low diversity of annual plants compared to the crust patch. In the edge there is high diversity. Grazing exclusion increased the diversity in the crusts but decreased the diversity under the shrubs and in the edge. Clear cutting of the shrubs didn’t affect the diversity in the crust and in the edge, but increased the diversity in the shrubs. Spiders and soil dwelling arthropods were affected differently. We present the mechanisms by which the shrubs affect the diversity and suggest an active managerial plan for increasing diversity of these organisms in a semi-arid ecosystem.