Ecological studies on Aerangis biloba (Lindl.) Schltr. (Orchidaceae) in NACGRAB field gene bank, southwestern Nigeria

Temitope Israel Borokini,Adedotun Onoyinka Afolayan

doi:10.11609/jott.o2728.3075-81

Abstract

Aerangis biloba (Lindl.) Schltr. belongs to the family Orchidaceae, which is listed as threatened under the Appendix II of the CITES. This study was conducted to estimate the population and distribution of Aerangis biloba in the field by National Centre for Genetic Resources and Biotechnology (NACGRAB), Ibadan, southwestern Nigeria. Twenty five sample plots of 50m by 50m each along line transects were randomly chosen and studies were carried out on them. The results were correlated with the factors that affect the distribution and survival of A. biloba. A total of 129 specimens of A. biloba were observed within the study area, giving a population density of 5.16 orchids per m2. This indicates that the species is abundant in the sampled area, as a result of good population of the selected phorophytes. The analysis of the data indicated a high correlation between and among the plots (P=0.0003). A. biloba was observed only on nine trees among over 160 trees present in the sampling area, suggesting that these nine trees could act as phorophyte for A. biloba of which, Irvingia gabonensis and Irvingia wombulu harbored the highest number of orchids. The paper gives a synopsis of the economic and ecological significance of orchids. It also recommends controlled harvesting, reduced deforestation and establishment of orchid gardens as some of the effective ways of enhancing orchid conservation in Nigeria.

Highlights

The family Orchidaceae comprises over 850 genera and an estimated 25,000 species representing about 10% of the world’s flowering plants and the largest family in species number (Roberts & Dixon 2008)
Most African epiphytic orchids were classified in the genus Angraecum in the mid 18th century and Lindley described this species as the ‘two-lobed Angurek’ - Angraecum bilobum (Stewart 1975)
A total of 129 Aerangis biloba were identified in the 25 plots sampled within the field gene bank of National Centre for Genetic Resources and Biotechnology (NACGRAB), Ibadan, Nigeria; giving a population density of 5.16 (Table 1)

Summary

Introduction

The family Orchidaceae comprises over 850 genera and an estimated 25,000 species representing about 10% of the world’s flowering plants and the largest family in species number (Roberts & Dixon 2008). A study of the notes attached to the herbarium specimens of Aerangis biloba at Kew revealed that most have been collected in dense forest in the Ivory Coast and on isolated trees in the savannah areas of northern Nigeria. Most of the plants collected in flower have been found in July and August, which is towards the end of the main rainy season in West Africa This indicates that the plants require plenty of water prior to blooming and have a specific and predictable blooming season that corresponds to seasonal rainfall and coordination of the life-cycle of its pollinators. It thrives when planted in a slatted basket with large pieces of bark (Stewart 1975). Epiphytic orchids contribute to the complexity, structure and function of the canopy, and are important components in terms of both biomass and species diversity; they interact with vast numbers of canopy invertebrates, as well as many vertebrate species (Nadkarni 1984; Ellwood et al 2002; Wolf & Flamenco 2003; Gravendeel et al 2004; Monteiro et al 2009)

Methods

Results

Discussion

Conclusion