Floristic Quality Index Value of Trees in Vallanadu Blackbuck Sanctuary, Thoothukudi, Peninsular India

Abstract

Floristic Quality Assessment (FQA) provides a standardized approach to evaluating ecological integrity by integrating species composition, abundance, and distributional rarity. In this study, we applied the Floristic Quality Index (FQI) to assess the floristic condition of Vallanadu Blackbuck Sanctuary, a tropical thorn forest fragment in Thoothukudi District, Tamil Nadu, India. Vegetation data were compiled from 700 plots (10 m × 10 m), recording 35 woody species. Conservatism coefficients (C-values) were assigned through a novel district-based weighting system that incorporates both nativity and occurrence frequency across Tamil Nadu’s 38 districts, thereby capturing regional rarity. The mean C-value was 6.17±2.02, resulting in an unweighted FQI of 34.34. Dominant species such as Vachellia mellifera, Commiphora berryi, and Ziziphus xylopyrus strongly influenced FQI values, while restricted taxa such as Fernandoa adenophylla contributed to the sanctuary’s regional distinctiveness. Overall, Vallanadu represents a moderately intact thorn forest ecosystem with conservation value for its biogeographic uniqueness.