Introduction:

Sustainable management of oases needs knowledge of the conditions of composition and diversity of the species living there.

Objective:

Estimating and comparing the diversity and structure of vegetation in the tree, shrub and herbaceous strata of the San Ignacio oasis, Baja California Sur, Mexico.

Materials and methods:

A total of 140 circular sites (500 m2) were randomly located, where 20 m2 and 1 m2 sites were nested to record the vegetation in the herbaceous, shrub and tree strata. Species richness, Shannon-Wiener, Simpson, Pielou and species importance value indices were used to estimate plant diversity in the strata and to characterize their structure.

Results and discussion:

A total of 53 taxa were distributed in 17 orders, 25 families and 47 genera. Richness, diversity and homogeneity were higher in the herbaceous stratum (S = 41, H´ = 3.21, J´ = 8.64, respectively) and lower in the arboreal stratum (S = 21, H´ = 2.01, J´= 0.688). Regarding the importance value index, the species with the highest ecological weight was Prosopis articulata S. Watson (33.35 %) for the herbaceous stratum, Cylindropuntia alcahes (F. A. B. Weber) F. M. Kunth (65.60 %) for shrub and Phoenix dactylifera L. (92.94 %) for the arboreal stratum.

Conclusions:

Vegetation richness and diversity were higher in the herbaceous stratum. This study represents a baseline of indicators useful for the evaluation of changes generated by natural or anthropogenic events in the San Ignacio oasis.

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