Invasive Prosopis trees in the hyperarid environment of the Dead Sea region

Invasive species cause enormous damage to ecosystems and are considered one of the main biotic factors contributing to the loss of global biodiversity. One of the most common exoctic plants in drylands is of the genus Prosopis, which has invaded natural ecosystems in many parts of the world. Despite the increasing presence of Prosopis spp. in natural areas, our knowledge of their function and impact in hyperarid regions is sparse. The goals of this study were to assess the state of the distribution of Prosopis trees in the hyperarid environment of the Dead Sea area, to characterize the habitats in which they established themselves, and the ways of dispersal in the area. Moreover, the study aimed to compare the functioning of invasive Prosopis and local trees, and to assess the impact that Prosopis has on native species. An extensive field survey showed that the seed sources of the invasive individuals are those Prosopis trees that were planted in populated areas. A combination of seed source availability, adaptation to a variety of substrates, and efficient dispersal vectors allowed this nitrogen fixer to invade natural hyperarid environments. Prosopis was shown to be more resistant to strong radiation, intense heat and high evaporative demand and showed a higher level of anisohydricity compared to the native Acacia tortilis. Higher nitrogen-to-phosphorus (N:P) ratios in Prosopis than in Acacia leaves indicated that Prosopis can accumulate higher amounts of N per unit of P than Acacia, which may be advantageous under these dry conditions where P availability is considered to be low. In addition, Prosopis exerted a negative impact on native Ziziphus spina-christi trees, the latter of which had a significantly lower water potential when growing in the vicinity of Prosopis trees than when growing near conspecific trees. The results of this research suggest that Prosopis may become a significant invasive species in the hyperarid environment of the Dead Sea region. A further rise in heat and drought as expected under climate change could increase the competitiveness of Prosopis spp. relative to the native tree species in the region, thus decimating their populations. To reduce the threat stemming from this invasive species, it is recommended to halt the spreading of Prosopis trees by eliminating the existing seed sources and banning livestock, a very potent dispersal vector.