Recently there has been a wide concern regarding reports of high mortality rates and lack of recruitment in the acacia populations throughout the Negev Desert and the Arava rift valley of Israel. Acacia trees in arid zones are considered to be `keystone species', having strong and direct influence over the entire ecosystem functioning and over the habitat biodiversity. Understanding the acacia response to drought stress and the essential factors for the longevity of the trees population is of high importance and essential in order to evaluate the entire ecosystem vulnerability.
This eco-physiology study will include and combine both long term field monitoring and controlled environment (greenhouse) experiments on acacia drought stress. The foundation of this current study is a continuously yearly based survey started at 2000 at seven plots in the Southern Arava. Each plot represents different types of ecosystem and hydrological regime. This survey provides a unique database of the acacia population dynamics during a sequence of dry years that ended in vast floods events during the winter of 2010. The most alarming finding of this survey is a lack of new seedlings found during the dry years and very few seedlings that were found to survive the summer after the 2010 winter floods.
In order to understand the physiological and morphological mechanisms of acacia seedlings under drought stress and the environmental conditions that enable recruitment, we will continue the conventional field monitoring and will investigate additional physiological and remote sensing tools in the field. In addition we will conduct experiments in a greenhouse on the three acacia species found in the Negev (A. raddiana, A. tortilis and A. pachycera). The first experiment will investigate the acacia species response to different water and salinity regimes. The second experiment will examine water pulse influence on the root development of acacia young seedlings. Those experiments results will be used to design additional experiments. Exploring the geo-ecophysiology aspects of acacia tree population in these years, can provide insights into long term impacts of climate fluctuations on the entire ecosystems in arid zones.
In this work we aim to combine different measurements methods consist of plant physiology and remote sensing of vegetation and study the contribution and performance of each of the above mentioned methods to sense stress indicators in acacia trees in particular and vegetation of arid zones in general. We will try to develop a technique that can be used as a long term ecological monitoring of trees in arid environments that will improve our understanding of the spatial and temporal changes of these populations.