**Abstract**

The dry vegetation of Ngazidja, Comoros Islands, is very rich in biological diversity. However, it is the most threatened and least known in this island. The purpose of this study is to provide ecological information about dry vegetation and to elaborate proposals for conservation. Data collection is ecological surveys, and ethnobotanical and socioeconomic surveys. Several floristic, and structural and soil parameters were processed and analyzed to characterize the sites. Five types of dry vegetal formations are identified: the dry forests of Lac-salé, Ngouni-Hamboda and Infoundihé-Chambouani, and the dry thickets of Singani, Domoni-Amboini, Hahaya. Eighteen surveys of 10 transects were undertaken. The forests are well stratified and the trees do not exceed 15 m high, with deciduous leaves. The density varies from 500 to 800 individuals per hectare in forest against 310 to 165 in thicket. A total of 103 species, belonging to 46 families, were recorded in these formations, including 70 trees and shrubs. Natural regeneration is only good for thickets and the dry forests of Lac salé and Infoundihé-Chambouani. Sustainable alternative solutions are proposed in order to improve the socioeconomic living conditions of the population and the conservation of biodiversity.

**Keywords:** dry vegetation dynamic, socio-economic, conservation biodiversity of ecosystems, Ngazidja, Comoros
