Decline Of The Negev's Acacias - A SpatiallyExplicit Simulation Model As An Aid ForSustainable Management

Abstract

In the Negev desert there is high concern about the high mortality and low recruitment of Acacia trees, a major source of livestock feed and firewood for the native Bedouins. The Acacias are mostly restricted to ephemeral riverbeds and areas with high ground water levels near oases. As the only trees in much of this desert, the Acacias constitute a major ecological concern in southern Israel. To develop sustainable conservation and management strategies it is necessary to understand the population dynamics of the trees. A spatially explicit, object-oriented computer simulation model is presented which is based on demographic data gained by field studies. As an example, we show first results of an application of the model to the ephemeral riverbed Nahal Saif which is cross-cut by a road. The road alters the flood regime. This leads to modifications in seed dispersal and reduces the water availability to the Acacia trees. It is shown that both factors have a negative impact on the population dynamics of A. raddiana. Culverts under the road would reduce the severity of this impact although this should be done in conjunction with the reintroduction of herbivorous mammals in order to facilitate seed dispersal and germination.