Abundance and spatial distribution analyses of Stemonoporus moonii Thwaites (Dipterocarpaceae) - a critically endangered species endemic to Sri Lanka

Abstract

Hora Wel Stemonoporus moonii Thwaites, a plant species endemic to Sri Lanka, is the central focus of this study. Because of its strictly narrow distribution area of fewer than 100 km2 and declining habitat, coupled with a high risk of extinction, it is placed under the ‘Critically Endangered’ category in International Union for the Conservation of Nature Red List category. A field survey was conducted during February–March 2020 in Walawwe-Watta Wathurana freshwater swamp forest to assess the population status of this species. Global positioning system (GPS) coordinates of individuals were documented. The root collar diameter of plants was measured to differentiate adults. Population size analysis was performed using GeoCAT online software, and a distribution map was prepared using Quantum GIS (QGIS 3). A total of 600 plants were recorded, with 50% each adult (root collar diameter more than 2.0 cm) and young individuals (root collar diameter equal to or less than 2.0 cm). The extent of occurrence (EOO) and area of occupancy (AOO) of S. moonii were calculated as 0.06 km2 and 4.000 km2, respectively. Two subpopulations of S. moonii can be seen within the Walawwe-Watta Wathurana Environmental Protection Area. The findings of the present study support the current IUCN Red List status of S. moonii as Critically Endangered. Even though the existing populations of this species located within a protected area and not presently exposed to major threats, the location is easily accessible and can potentially be affected by anthropogenic pressures and habitat loss. Therefore, this species and the habitat warrant suitable in situ conservation measures.