Monitoring and conservation of the rare orchid Didimoplexis verrucosa in the face of change

Abstract

Abstract Background: Didymoplexis verrucosa is a cryptic leafless saprophytic ground orchid (~70 mm tall) growing on the coastal forest floors of southern Zululand and classified as Vulnerable (D2). As part of a population monitoring programme, 960 man-hours of species specific searching over five consecutive flowering seasons were conducted, yielding only one individual plant. Objective: The aim of this study was to increase detection rate by developing a profile of environmental indicators for the accurate identification of suitable habitat. Methods: A detailed description of suitable habitat was compiled based on the Braun-Blanquet approach. Results: The results showed that key attributes shared by localities include similar topographic position in the landscape, hydrology, soils, vegetation composition and structure, forest age, leaf-litter composition of the forest floor, the co-occurrence of Isoglossa woodii, and a similar degree of protection from sunlight, wind and desiccation. Significance of the findings: This profile of essential habitat characteristics can be used as a surrogate in the absence of actual locality data when identifying target conservation areas and compiling management strategies for this very cryptic species. A by-product of this habitat analysis was the discovery of a long list of impacts on the long term survival of D. verrucosa. The combination of these stochastic and deterministic events will drive habitat change at rates beyond the species’ ability to adapt. Managing these variables forms the crux of its successful conservation. A conservation status revision, based on the formal IUCN criteria, indicate that D. verrucosa should be reclassified as Critically Endangered Category B2a and D.