1. Mr. Ariel Meroz

Human activity impacts vegetation, however, attributing the extent of changes to which is the result of human actions or of climate variability is challenging. The Israeli Negev desert is bordered by two countries (Egypt and Jordan), and by the Palestinian Authority (Gaza Strip and the West Bank), crossing three climate zones and a variety of soils and lithologic settings. Desert vegetation was traditionally subject to herds grazing, mostly done by the local Bedouin (semi-nomadic) community. Due to the extensive grazing, trampling, bush gathering, and rainfed agriculture by Bedouins, and other human land uses such as military training areas and protected areas, the anthropogenic impact on desert vegetation is hard to evaluate. We chose to use large-scale exclosures such as national borders and six military bases to estimate the different impacts that grazing and bush gathering have on vegetation cover and thus to isolate the human factor from the climatic factor. We used remotely sensed derived proxies of vegetation (the Normalized Difference Vegetation Index, NDVI) and surface albedo from Landsat and MODIS satellites to estimate the anthropogenic impact on vegetation cover in the past four decades (since 1984 – 2019). Our results showed that the cross-border differences in grazing and bush gathering led to a significant impact on vegetation cover within exclosures. These cross-border differences were more pronounced in the semi-arid and arid climate regions and decreased in the hyper-arid region. We also found that the sandy soil bed was the most active environment for vegetation growth in the arid environment, causing the most profound difference between the two sides. Exclosures thus provide a natural experiment which enables us to test the factors driving changes in natural vegetation.