RELATIONS BETWEEN BIODIVERSITY, DESERTIFICATION AND CLIMATE CHANGE
by Prof. Uriel N. Safriel
Jacob Blaustein Institute for Desert Research, Ben Gurion University of the Negev and Department of Evolution, Systematics & Ecology, Hebrew University of Jerusalem
Editor’s Note: This paper is part of a longer study, entitled "Problems and Long-Term Goals of Conservation of Biodiversity in Israel" which was submitted to the Ministry of the Environment within the framework of its strategy for sustainable development. These and similar issues will be discussed in an Expert Meeting on Synergies among the Conventions on Biodiversity, Climate Change, Combating Desertification and the Forest Principles which will take place at the Blaustein Institute for Desert Research at the Sede Boqer campus of Ben Gurion University of the Negev in March 1997. The meeting will provide an opportunity to discuss key aspects of these international instruments and to recommend measures to promote the synergies in their implementation.
Several international legal instruments addressing sustainable development were adopted during the past few years, including: the Convention on Biological Diversity, the Framework Convention on Climate Change and the Convention to Combat Desertification and Drought. These instruments deal with issues that are intrinsically related and interconnected since the road to sustainable development entails the safeguarding of biodiversity from climate change and desertification, which in part are caused and are definitely exacerbated by damages to biodiversity. To a large extent, inappropriate agricultural practices and non-sustainable rural development and land management are responsible for this vicious cycle of interactions and feedbacks between loss of biodiversity, deforestation, desertification and climate change. Israel provides an interesting case study for the synergies between these three phenomena.
DESERTIFICATION AND BIODIVERSITY
The UN Convention to Combat Desertification (1995) defines desertification as "land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities." These vulnerable drylands comprise about 40% of global lands, of which at least a quarter are already degraded. It is generally agreed that desertification most frequently results from development which is not sustainable, due to the mismanagement of biodiversity: overexploitation of vegetation cover leading to topsoil erosion and hence reduced productivity, or improper water use resulting in salinization. This affects not only crops but also rangeland and its biodiversity.
Overpopulation and increased demands, mostly in semiarid regions, bring about overexploitation of fire wood, overstocking, overgrazing and trampling, and the transformation of rangelands (with year round vegetation cover) to croplands (with intermittent vegetation cover). The reduced vegetation cover, the breakage of the biogenic soil crust, and the development of a physical soil crust, lead to topsoil erosion. The soil loses the recycled minerals, the organic matter, the moisture-retention potential and the seed bank. Furthermore, irrigation brings about salinization of the topsoil. This is because the scarcity of water does not allow the application of quantities sufficient for leaching, and the high evaporation leaves the salt in the topsoil. Such croplands, when abandoned due to salinization, cannot revert to their original function as rangeland, since most range species are intolerant of the increased salinity. Thus, either due to loss of topsoil or due to salinization or both, land degradation reaches the point of irreversibilitydesertification. Increasing water supplies, enabling the intensification of rangeland utilization and turning rangelands to croplands in semiarid regions, leads to non-sustainability.
When the transformation of rangeland to irrigated cropland results in desertification, the effect on biodiversity is in the loss of natural ecosystems. When the overexploitation of rangeland results in desertification, the effects on biodiversity are first expressed in the direct loss of plant species and the animals associated with them, and laterin the loss of topsoil and the potential for rehabilitating biodiversity. These biodiversity losses, both in goods and services, further exacerbate desertification in the affected areas. They also affect adjacent and other areas, that used to enjoy some of the services, such as aquifer recharge for example.
CLIMATE CHANGE AND BIODIVERSITY
Climate change, mainly global warming, results from non-sustainable development: emission of greenhouses gases coupled with destruction of their natural sinksvegetation. Reduction of soil plant cover in drylands due to the desertification process causes further reduction of sinks, i.e., global warming, which in turn exacerbates desertification. Warming increases evapotranspiration hence aridity, thus bringing more drylands under the risk of desertification. Loss of surface moisture due to desertification releases solar energy, otherwise expended on evaporation, to warming of the lower atmosphere. This increases warming and reduces rainfall. Thus, desertification and climate change are interlinked by positive feedback relations. Desertification and climate change are therefore a manifestation of non-sustainable development. Desertification can result from non- sustainable water resource development and use, and climate change may further reduce water supplies.
The current prediction for the effect of climate change in Israel is that of reduced soil moisture and aquifer recharge due to increased evapotranspiration, despite the possible increase in future precipitation.
Desertification is caused by reduction of biodiversity and causes further reduction of biodiversity. Reduction of biodiversity reduces carbon sinks hence increasing climate change. Thus, it is the loss of biodiversity that initiates the vicious circle of desertification-global warming-further loss of biodiversity. There is one difference, though, between desertification, climate change and loss of biodiversity: if emissions are reduced, the climate system can be restored; if rehabilitation measures are taken, desertified land may be reclaimed. But a species lost, or even a component of its genetic diversity lost, cannot be reconstructed or resurrected. Thus, the predicted warming of Israel may result in loss of drought-sensitive species and with themthe impairment of ecosystem services.
PERIPHERAL POPULATIONS AND CLIMATE CHANGE
However, the prospective loss of biodiversity due to global warming may still be mitigated by an exploitation of the genetic diversity of species living in the semiarid ecosystems of Israel. There is a growing amount of evidence supporting a theory which suggests that geographically peripheral populations of a species, as compared to the populations of the same species inhabiting core areas of its geographical distribution, are living under low environmental stability, have high within-species diversity, high evolutionary potential, and most importantlyhigh resistance to environmental changes, hence persistence under the forecasted climatic change. There are therefore climate change scenarios that will cause core populations of drought-resistant species to become extinct due to their low genetic diversity (hence a lack of drought-resistant genotypes), whereas peripheral populations will persist and could be used to rehabilitate the core areas of distribution of their species. This is not to say that the semiarid peripheral populations, if protected from development and desertification, will not be affected by climate change. Climate change will act as a selection agent, that will eliminate the non-resistant genotypes and thus will reduce genetic diversity. But the populations will persist and will be used for rehabilitation of the core areas. The rehabilitated population of a given species will differ in its genetic structure as compared to the extinct oneit will be composed predominantly of drought-resistant genotypes, originating in the semiarid region. But the species will persist, and the ecosystems will not be damaged.
The semiarid belts sandwiched between the arid and the dry subhumid belts, constitute climatic transition areas, between the "desert" (arid and hyperarid) and the non-desert (dry subhumid), in which species, both arid and dry subhumid ones, reach their distributional peripheries. Therefore, the semiarid regions constitute a repository of unique within-species biodiversity, with great evolutionary potential for rehabilitation purposes. Thus, the conservation of habitats in the semiarid region constitutes a climate change mitigation strategy.
Is there indeed a high incidence of peripheral populations in semiarid regions? A survey of the Israeli bird species, for example, quantified the degree of peripherality of the 200 Israeli breeding bird species, on a scale of zero to one. It was found that of the 124 species which have the highest value of the peripherality index, 100 have Israel as their southern periphery, and 17 and 7 have Israel as their northern and eastern periphery, respectively.
Within Israel, the semiarid region is the one richest with peripheral populations. It is also the region within which the "desert edge," as expressed in the isohyete that determines the transition between rainfed and irrigated agriculture, pulsates vigorously between years. These pulsations make the species that live in the semiarid region of Israel experience desert climate during a sequence of years, and a non-desert climate in a subsequent series of years. This is presumably what maintains a high genetic diversity in the peripheral populations. Indeed, it was found that the genetic variability, as expressed in isoenzymes’ variability, increased in the Israeli chukar partridge Alectoris chukar, from the core to the periphery, namelyfrom the dry sub-humid to the arid region.
As shown earlier, semiarid regions are most prone to desertification. At the same time, these regions harbor biodiversity that may be significant for future mitigation of the detrimental effects of climate change elsewhere. The natural habitats of the semiarid belts should therefore be protected, both from desertification and from agricultural development, so that they can serve as repositories of biogenetic resources used in the future for rehabilitation of ecosystems of other regions, should they be damaged by climate change.
In the 1950s, David Ben-Gurion, Israel’s first Prime Minister, coined the slogan "if we don’t conquer the desert, the desert will conquer us." The transport of water to the Negev through the National Water Carrier from Lake Kinneret, some 200 kilometers away, did indeed help "green" the semiarid belt of the Negev. But at what cost? The transformation of this traditional rangeland to fertile irrigated cropland was at the expense of biodiversity, whose prime significance is in the value of its biogenetic resources. Today, as the synergies between biodiversity, climate change and desertification are becoming better known, it is imperative to find new ways of incorporating the value of Israel’s semiarid region, as a repository for biogenetic resources, in development plans for this region.