Change of oases farming systems and their effects on vegetable species diversity: Case of oasian agro-systems of Nefzaoua (South of Tunisia)

The paper discussed the change of oases cropping systems and their effects on vegetable species diversity. The change of oases cropping systems especially the intensification of date palm production and the introduction of new vegetable varieties with more commercial interests have led to the marginalization of local and traditional varieties. These varieties have genetic traits such as tolerance to salinity, to high temperature, to drought, to water deficiency and to resistance to pests and parasites. The identification and evaluation of the vegetable diversity are the basis of its conservation and sustainable use. In this study, several floristic and species diversity indices were used to evaluate vegetable diversity of the region in the three types of oases agricultural system in the 120.84h surveyed area. Different cropping systems and farming practices were described to evaluate the effects of cropping system change on the vegetable diversity. The total Shannon–Weiver indice value in the studied region was 3.3. This measured value is below the maximum of diversity (Hmax=4.17). Thus vegetable species were not equally represented in the oases of Nefzawa region. Significant differences in the vegetable diversity indices were detected between public oases: ancient and modern ones (they form a homogeneous statistical group) and private modern oases. The maximum diversity indice values were observed in the private modern oases type. The oases cropping systems structure varied at different crop floor in the three types of oases. This evolution was defined as a trend toward intensification of oases agricultural system by the monoculture of “Deglet Nour” date palm variety, exploitation of large oasis area, water irrigation requirements and high use of chemical in-puts. To conclude, this study has showed that the new agronomic and socio-economic trends of oases agro-systems improve their profitability, but threaten their sustainability by poor management of local plant genetic resources and overexploitation of available water resources.