Low soil fertility? Most arid and semi-arid areas actually have fairly high soil fertility. There are several techniques that have done well to increase rehabilitation and biodiversity in these areas, including certain types of pulse grazing management, contouring the landscape, and reforestation through the use of drought tolerant species.

From development-cooperation works in Syria / Arab League and Timbuctu / Sahel-Zone and Afar-+Somali-Region of Ethiopia I can give these orientations to enhance biodiversity: A) The soils contain a well-established high number of diverse hidden / still viable, often old seeds, which start germinating once the area is protected from herds / animals by any type of fencing. B) On a small strictly-fenced research-area of e.g. 100 sq-meter one can test this potential, esp. after irrigation within a few months. C) The analysis of feaces / dung reveals astonishing figures of seeds per kg of grazing animals, which are transported over far distanced esp. by pastoralists / nomads and can contribute do biodiversity. D) In Afar- and Somali-Region of Ethiopia the pastoralists have breathtaking re-vegetation-results on large areas after fencing and creating a semi-sedentary habitat. E) The famous Belgian missionary's Acacia-approach in Sahel-zone leads also to a new diversity in pasture-regrowth in the protected area. F) Barbed wire and natural fences, esp. Acacia-branches or Euphorbia-hedges are the key- and corner-stone for re-vegetation and biodiversity in semi- and arid areas. G) Ethiopia and Rwanda --- as example --- are well ahead with strict prevention of uncontrolled grazing.

Depends on what is intended. The arid and semiarid regions of the Iberian Peninsula contained the greatest proportion of Iberian endemic plant species, even greater than Mediterranean high mountain areas. Then it's not just a question of diversity; also need to assess the specificity and uniqueness of the much of the flora of arid areas.

Hi Mohammed: Here is an link which could be useful for you. In this study the summaries of selected case studies and innovative experiences have been discussed.

http://earthmind.net/slm/docs/unep-2002-arid-case-studies.pdf

Regards