Reproductive adaptations and the availability of pollinating vectors in white Indian teak (Gmelina arborea Roxb.) in tropical rain forest of Indo-Burma Hotspot

Abstract

For the effective management of economically and ecologically valuable tree species, it is crucial to understand pollination and resource allocation particularly in biotic pollinated species. Gmelina arborea Roxb. growing in moist tropical forest of Indo-Burma region has high economic value for the pulp and paper, quality timber, medicines and a valuable component of agroforestry systems. We studied floral morphology, pollinating vectors and the reproductive potential of the species in natural forest during the flowering and fruiting seasons (March-June) of the years 2012 and 2013, which covered about one month period in each year. Floral morphometric traits, pollinating vectors, pollination and fruit formation were observed during the flowering season on ten randomly selected individuals within the population. Floral characters exhibited strong adaptations towards entomophily with emerging adaptation towards ornithophily. G arborea flowers were mainly visited by two legitimate functional groups of pollinators’ i.e. insects (e.g. Xylocopa violacea, Amegilla cingulata, Mylabris pustulata) and five birds species belonging to 2 families of order Passeriformes. Additionally, one species of squirrel (Callosciurus pygerthus) was noted to legitimately foraging the flowers. Xylocopa violacea ascertained highest visiting frequency over other pollinators. Xylcopa bee also exhibited high level of functional synchronization with floral morphology of G. arborea and ascertained as most important pollinator in the study region. However, long billed trait of passerines birds were important determinant for the bird species to act as potential pollinators in the species. Ornithophilic adaptation in G. arborea is key feature of the species to attract the birds and facilitates reproductive effort. There is significant role of both flower and pollen production (resource allocation) and availability of pollinating vectors (pollination limitation) in reproductive success. G. arborea shall be vital for insects and birds conservation through providing floral resources in natural forest and agroforestry land setting.