As we have already seen, the ecosystem of the northern Negev is regulated by a source-sink dynamic between areas of topsoil crust and areas of vegetation. The topsoil-crust areas generate runoff water, erosion, nutrients and seeds, which are absorbed and stored in the vegetated areas, where they contribute to increased fertility, productivity and biological diversity.
The limans can be likewise regarded as large sinks that absorb water, soil, nutrients and seeds from their arid surroundings, thereby increasing their own productivity and biodiversity, together with the biodiversity of the desert landscape as a whole. It should be emphasized that no ecological research has been conducted on biodiversity within limans, but from research carried out in areas of extensive desert afforestation in Yatir and Sayeret Shaked Park, which uses various methods of runoff harvesting, we can perhaps draw conclusions regarding possible processes.
In these areas, as a result of the runoff-harvesting and afforestation techniques used, an increase was found in the productivity and diversity of herbaceous vegetation, arthropods (i.e., insects, arachnids, etc.) and birds.
The creation of areas of differing microtopography, where ground moisture levels are higher than in the surrounding arid topsoil-crust desert environment, provides a trap for runoff and seeds, and allows denser germination of herbaceous plants whose large seeds are spread by runoff and wind. As a result, a clear difference in the composition of annual plant populations was found to exist between the natural areas and the artificial areas that benefit from runoff harvesting.
The pits used for runoff harvesting were found to contain a greater wealth of common varieties and Mediterranean species that are usually found in the desert only in areas where resources and humidity are greater.
In view of anticipated climate change and increasing desertification, the contribution these artificial areas can make is even greater: they can now be regarded as providing a form of sanctuary for these species and for the conservation of biological diversity in the desert landscape.
Another possible role for the limans, as sites comparatively rich in resources and flora amidst an arid environment, is their high potential for attracting migratory birds, which may find them to be sources of food in the spring and autumn. The conservation and support of vital biological processes such as bird migration is, therefore, another important potential liman contribution to biodiversity.
On the other hand, there are fears that phenomena such as changes in the composition of the ecological population (changes of this kind have been discovered by research into flora, birds and reptiles in areas where runoff harvesting is used in forestry), may lead to the disappearance of desert-dwelling species that may be preyed upon or pushed out by competition. For example, research on reptiles conducted in Sayeret Shaked Park showed that local desert variety of lizard had disappeared as a result of greater predation by species of raptor that use trees as vantage points.
These desert varieties were replaced by widely-distributed Mediterranean species that appear to be better adapted to an environment where trees and raptors abound. The Beersheba valley, where the soil is loess mixed with quartz sand, serves as a habitat for a wide variety of species whose numbers are dwindling because of destruction and restriction of their natural habitat due to increased building, infrastructure extension and agriculture in the area. Local varieties of plants, reptiles, rodents and birds, such as the Negev iris, the Gilead iris, the leopard fringe-fingered lizard, the marginated tortoise, the lesser Egyptian jerboa and the houbara bustard are today in danger of extinction both regionally and worldwide.
The intrusion of widespread Mediterranean varieties into these newly created habitats is liable to result in competition or high predation pressure for local species already under the threat of extinction.
The hooded crow, for example, is a notoriously invasive Mediterranean species that has spread throughout the Negev in the wake of environmental change, causing serious damage to local species because of the pressure of high predation. Hooded crows prefer to nest in eucalyptus trees and they feed off the abundant food scraps often left in limans and forests. In order to conserve sensitive local species, spot treatments for invasive species like these have to be devised.
As the limans are intermittent features of the landscape, the chance that one of these Mediterranean species will use them to penetrate and settle the Negev, thereby pushing out the local desert species, would appear to be small.
We should bear in mind that settlement, agriculture, afforestation and roadside environments probably have a very much greater impact in this regard than the limans do. These issues have not yet been examined with regard to the limans; it would probably be a very good idea to monitor and research their ecology, perhaps with the help of the hydrological monitoring stations already in operation.