Biodiversity assessment in tropical wet evergreen forest: species composition and evaluation of sampling designs

Speaker : Dr. Ayyappan N., Researcher, IFP

Organisers : Department of Ecology, French Institute of Pondicherry.

Venue : Main Indology Hall, French Institute of Pondicherry, 11, Saint Louis Street, Pondicherry - 605 001.

Time : 10.30 am

Abstract

Species richness is the simplest and straightforward means to describe biodiversity among its components and it underlies many ecological models and conservation strategies. A wide range of sampling methodologies has been employed to measure this metric importantly to deal with the fact that the richness of species in a community usually cannot be observed directly because a complete enumeration of every species is seldom feasible. In practice, a sample of a community is assessed and more often small sample plots are frequently used for rapid assessment of biodiversity.

This presentation evaluates biodiversity assessment of trees (stems > 1 cm dbh) inventoried by employing two sampling designs - a contiguous (0.5hectare; 100 m x 50 m) and non-contiguous systematically laid 120 quadrats of 5 m x 5 m (totaling 0.3 ha) spread out within a in 30 ha plot of a tropical evergreen forest at Varagalaiar, Western Ghats, India. Altogether 124 species and 3,375 stems were enumerated. Although the two sampling designs harbored equal species richness (98 species in contiguous 0.5 ha and 99 in non-contiguous 0.3 ha), the species accumulation curve was steeper for non-contiguous sample than for the contiguous design. Both species-area and species-individuals rarefaction curves displayed similar trends for both the sampling design. Non-contiguous 0.3 ha area captured 33 exclusive species (33.3%) while contiguous 0.3 ha yielded 20 species as exclusives (23.3%). The two sampling designs shared 66 species.

Shannon and Simpson diversity indices were greater for non-contiguous sample, but the differences were minimal. One-way ANOVA revealed that the sub-samples of 0.025 ha, 0.05 ha, 0.1 ha and 0.15 ha of the two sampling designs did not differ significantly in species density, stem density (except for 0.025 ha) and basal area, which indicated the homogeneity of the studied area. The features such as occurrence of more number of trees, conspecifics, and relatively less number of exclusives and rare species in the contiguous sample design rather than the non-contiguous sample, could be the reason for the variation in species density between the sampling designs.