Pollen limitation failing reproductive success in selected animal pollinated trees of tropical moist deciduous forest of north-eastern hill region, India

The aim of this study was to estimate reproductive effort and success in tropical trees and to examine the effect of pollen limitation on reproductive success. Pollen limitation was assessed through pollen supplementation experiment to contrast the open pollination treatment. The taxa selected were Bombax ceiba, Erythrina stricta (ornithophilous trees), Lagerstroemia speciosa, Mesua ferrea and Schima wallichii (entomophilous trees). Index of pollen limitation was highest in Bombax ceiba and Erythrina stricta (both self-incompatible species). The remaining three species were partially self-incompatible with favouring selfing in Lagerstroemia speciosa and Mesua ferrea and supporting outcrossing in Schima wallichii. Therefore, the high index of pollen limitation in Bombax ceiba and Erythrina stricta might be due to the effect of either lacking quality pollen or lacking bird pollinators. All five species produce a large amount of pollen at individual tree level in the order of 108 (Erythrina stricta) to 1010 (Mesua ferrea). Fruit and seed set following pollen supplementation were higher than the open pollination (as control) in all studied species. Pollen limitation in this study is likely associated with the effectiveness of pollinator and their frequency, as all the studied species had produced ample pollen at tree crown level which ultimately leads to pollinator resource limitation in tropical trees.