Taxonomy, seed morphology and ecology of great hornbill dispersed rainforest trees of the anamalai part of the southern western ghats, Kerala

Abstract

The tropical evergreen forests of Anamalai part of Southern Western Ghats are particularly special as it contains the entire range of natural vegetation rich in species diversity and endemism. The great diversity of this area is due to bioclimatic, physiographic and edaphic factors and also due to the presence of pollinators and seed disperses. The Great hornbill is in proximity of evergreen forests at an elevation from 250 meters to 1500 meters above sea level. According to IUCN Red List Category, Great hornbill is classified as vulnerable (VU) due to habitat loss. The diet of the Great hornbill consists mainly of fruits. Fruits of some important plant species of tropical forest coming under families such as Moraceae, Lauraceae, Myristicaceae, Annonaceae and Meliaceae constitute major part of the diet of hornbill. They feed on large fruits and regurgitate the seeds intact. They deposit a great number of seeds under the nesting tree during breeding season and thus serve as important agent for maintaining the habitat equilibrium of primary forests. They also move over large distances, possibly regurgitating and defecating the seeds far away from the parent tree. The present study attempts to find the mutualistic relationship between Great hornbill and these trees. The plant species selected in the study area belongs to Lauraceae (24 species of 8 genera), Meliaceae (6 species of 5 genera), Myristicaceae (3 species of 2 genera) and Elaeocarpaceae (2 species of genus Elaeocarpus). Some of the recorded species include Canarium strictum of family Burseraceae, Diospyros crumenata of family Ebenaceae, Syzygium cumini of Myrtaceae, Palaquium ellipticum of Sapotaceae and Maesopsis eminii of Rhamnaceae. These species come under vulnerable or endangered category and are endemic to Western Ghats expect Maesopsis eminii, which is an exotic species. A detailed taxonomic study was done for these species and an identification key was prepared. The fruits of these plants were collected in various stages of development up to mature stage. Detailed morphological studies were done, and an identification key based on fruit and seed characters was prepared. Phenology of the selected species was done, and it showed that the fruiting period of these trees corresponds with nesting time of hornbill. Germination experiments were carried out to check the seed viability as well as to etermine if there was any difference in germination in regurgitated vs. fallen (control) seed. Germination was tested ex situ in the rainforest field station at Malakkappara. Study showed marked variations; regurgitated seeds of all the species showed fast germination than controlled seeds. In order to find out the species diversity and sapling diversity, quadrat study was done around the nesting tree (square plots of 0.16 ha) at 8 locations in Vazhachal, Sholayar and Parambikulam forest divisions. Phytosociological parameters as well as saplings and seedling regeneration were noted. The study showed that most species found in these areas are hornbill dependent species. Seedlings of 21 food plants were recorded beneath the nesting tree, more seedlings were found in front of the nest than behind. Most of the seedlings were of Myristica, Persea, Palaquium, Knema and Dysoxylum. Even though the seeds of many of these species are eaten by various animals like macaque, giant squirrel etc. they crush the seeds while eating and are not efficient seed dispersers. Great hornbill, however, regurgitates the seeds intact and acts as an important seed dispersal agent. Great hornbill and these forest trees maintain a mutualistic relationship.