Analysis of the population dynamics of Acacia trees in the Negev desert, Israel with a spatially-explicit computer simulation model

Most trees in the Negev desert, Israel, are either Acacia raddiana, A. tortilis or A. negevensis. They provide food and shelter for many desert animals and are a major source of livestock feed and firewood for the native Bedouin people. High mortality and low recruitment of these trees have been reported. To develop sustainable conservation strategies it is necessary to understand the population dynamics of the Acacia trees. Therefore, on the basis of demographic data gained by field studies, a spatially-explicit, individual-based computer simulation model of the population dynamics of A. raddiana has been developed. We evaluate the relative importance of different processes such as seed production and seed infestation by parasites, germination, mortality, and mistletoe infestation to the survival and recruitment of Acacia trees in the Negev. Mortality rates at different life stages, the production of uninfested seeds and the weather regime were most influential. The infection of trees by semi-parasitic mistletoes proved to be of minor importance. The most important result is that an increase in the germination rate of Acacia seeds, such as may result from passage through the digestive tract of large mammalian herbivores, is capable of counteracting the detrimental effect of unfavourable climatic conditions. Consequently, we discuss the use of increased large mammalian herbivore densities as a possible management option for enhancing the survival of Acacia populations in the Negev.