Entomophily, ornithophily and anemochory in the self-incompatible Boswellia ovalifoliolata Bal. & Henry (Burseraceae), an endemic and endangered medicinally important tree species

Abstract

Boswellia ovalifoliolata (Burseraceae) is a narrow endemic and endangered deciduous tree species. Its flowering, fruiting and seed dispersal events occur in a leafless state during the dry season. The flowers are small, bisexual, mildly odoriferous and actinomorphic; weakly protandrous but strictly self-incompatible. While insects and sunbirds pollinate the flowers, floral characteristics suggest that entomophily is the principal mode. Both bud and flower feeding by a weevil and flower and fruit feeding by the Palm Squirrel have been found to affect the success of sexual reproduction. The Garden Lizard serves as a predator of pollinating insects, especially bees and wasps, thus influencing pollination of this tree species. Fruit set in open pollination is below 10%, rising to 34% in manual cross-pollination. Limitation of cross-pollination, space constraints for seed production from all flower ovules and availability of limited resources in rocky, dry litter of the forest floor appear to constrain higher fruit set. Mature fruits dehisce and disseminate their lightweight, papery winged seeds with the aid of wind. The study site being windy provides the necessary driving force for effective dispersal of seeds away from parent trees. Seed germination occurs following rainfall but further growth depends on soil water and nutritional status. The success rate of seedling recruitment is highly limited, and it could be due to nutrient-poor soil and water stress resulting from dry spells during the rainy season.