Comparison of two vegetation sampling methods in plots of variable area in Bicuar National Park, Huíla-Angola

Abstract

The present work compared the two vegetation sampling methods in the Bicuar National Park, with 30 plots (20 m × 50 m) and 3 plots (100 m × 100 m), in terms of sampling sufficiency – calculated from species accumulation curve; description of structure and species composition – calculated from the principal phytosociological parameters, as well as diversity, dominance and specific  richness  – calculated from Shannon Diversity Index (H’), Simpson Dominance Index, (D’), Margalef Richness Index  (I’) and equitability calculated by the Jaccard Equitability Index (J’). The obtained results points to a density of 1415 individuals, belonging to 15 botanical families and 46 species with 20 m × 50 m method and 1422 individuals, of 9 families and 28 species using the method of 100 m × 100 m. Being Fabaceae the most representative family. Relatively sampling sufficiency, the 30 sampling plots showed to be enough to describe the composition of species for this study. As long as the curve reached the stability with this number of sampling unities. However, in terms of diversity, dominance, richness the plots of 100 m × 100 m showed to be more efficient, implying that in bigger plots there are more possibilities to include major diversity, by the existing chance of sampling new species which have not sampled in the group of smaller plots. In both methods there was a certain uniformity between species, with the similarity index value to be above 0,50. It should be noted that, despite the operational costs, larger plots, installed permanently, offer the possibilities of future re-measurement of individuals, which allows us monitoring the vegetation dynamics, taking into account the various factors of disturbance from different sources that today threaten the park.