**2.2 Collection of data**

**262** The Phytoecological study was used. Surveys were conducted between October 2019 and January 2020 and between April and July 2020 to maximize the chances of harvesting easily identifiable, fertile specimens. The sampling was based on:

*Phytoecological Study, Ethnobotanical and Dynamic of Dry Vegetation in the Ngazidja Island… DOI: http://dx.doi.org/10.5772/intechopen.107330*


Eighteen (18) surveys and 10 transects following a North–South gradient, perpendicular to the sea, were delineated. Part of species was identified onsite, another part was identified at the INRAPE herbarium and the rest with the flora of Madagascar and Comoros [15] with the databases samples of the herbarium of the Museum of Natural History of Paris [16] and the Herbarium of Mayotte on the basis of the National Botanical Conservatory of Mascaraing.

Species density was assessed by counting trees with a diameter at breast height greater than 10 cm. This DBH is established from the measurement of the circumference using a tape measure. The size of the trees was evaluated by the total height (Ht), measured using a clisimeter.

Physiomomic analysis, floristic diversity and similarity: Quantitative vegetation parameters (density, basal area, regeneration, species richness, biological spectra, maximum tree height) were used to characterize the types of vegetation.

For the study of natural regeneration, the Placeau method was used and consists in measuring the diameter of all the individuals of each species present in a 1 ha plot. Those iIndividuals are classified into two categories: regenerated species (DHP <10 cm or Nr) and seed species (DHP ≥ 10 cm or Ns). The regeneration potential is expressed by the number of regenerated individuals over the number of seed-bearing individuals, expressed by the regeneration rate (TR): TR (%) = (Nr/NS) X 100


Threat assessment on dry vegetation formations: Ethnobotanical surveys were conducted among local populations, 200 individus, in 14 localities bordering the study sites: Singani, Dzhadjou, Sima-Ambouani, Ifoundihé-chambouani, Ikoni, Moroni, Hahaya, Domoni-Ambouani, Domoni-Adjou, Ntsaouéni, Bangoua-kouni, Ouella, Ivoini and Ouémani. They understand the interactions of local communities with plant resources (different uses) as well as the threats that weigh on the habitats. Observations were also made in the field. The formula of [17] was used to evaluate the species utilization index in order to know the species that were widely used. The people concerned above all are those who appear to have a direct or indirect impact on dry forest or thicket: lumberjacks, wood traders, collectors of medicinal plants, peasants, carpenters, carpenters, farmers, head of non-governmental associations. These surveys were carried out collectively or individually, in the form of semi-direct interviews with semi-open, open or sometimes closed questions asked to men (65%) and women (35%) between 18 and 70 years old. The information is collected using a dictaphone.
