Effect of Environmental Factors on Pollen Viability of Tropical Trees in Garhjungle Sacred Forest Of West Bengal, India

Abstract

Tropical trees of Garhjungle sacred forest, West Bengal, India may change in pollen viability according to pollinator, flower exposure, and pollen predacious thrips. A pole clipper system was used, and in vitro viability measures, to evaluate relative impact of such factors in six forest tree species. Relative pollen viability was measured with Alexander’s stain, or TTC stain for Madhuca indica Gmelin. (Sapotaceae); Buchanania lanzan Spreng. (Anacardiaceae); Pterocarpus marsupium Roxb. (Fabaceae); Alangium lamarckii Thw. (Alangiaceae); Schleichera oleosa (Lour.) Oken (Sapindaceae) and Tectona grandis Linn. (Verbenaceae). The impact of thrips was gauged from bagged and open flowers, and direct counts on flowers in Buchanania and Tectona; canopy position impact (affecting light, exposure, temperature) was gauged using collections made with pole clippers, and by reciprocal transfer of inflorescences on branches. Four native bee species were scored for viable pollen as they first left their nests in early morning. Viability decreased according to thrips presence in Buchanania and Tectona. The former had more thrips and significant damage only among lower flowers, while the latter showed most thrips damage on higher flowers. Pollen viability was higher on the higher flowers in Tectona, Madhuca, Buchanania, Pterocarpus, Alangium and Schleichera. Pollen viability in transplanted inflorescences changed in Tectona, Madhuca, Buchanania, Pterocarpus, Alangium and Schleichera. Viable pollen was recovered on native bees first leaving their nests in early morning, indicating prolonged pre-pollination potential. Various factors influence pollen viability in tropical field conditions. Thrips may effectively remove a large portion of pollen and exert more influence than physical exposure. Some flowers increase in pollen viability when exposed to gap conditions, but others show the opposite trend, with implications for degraded habitats. Bees may secondarily disperse viable pollen from their nests, in which it retains viability from one day to the next. Relative pollen viability was in agreement using different in vitro tests.