Reproductive ecology of Shorea roxburghii G. Don (Dipterocarpaceae), an Endangered semievergreen species tree of peninsular India

Abstract

Shorea roxburghii is an Endangered semievergreen tree species restricted to peninsular India in the Eastern Ghats. Leaf shedding and leaf flushing are annual events while flowering is not annual, but when it does flower, in March, it shows massive blooming. Massive blooming, drooping inflorescence with pendulous flowers, ample pollen production, gradual pollen release as a function of anther appendage and aerodynamic pollen grains - all suggest anemophily. The characteristics of nectar secretion, hexose-rich sugars and amino acids in nectar are additional adaptations for entomophily. The plant is functionally self-incompatible, obligately outcrossing and ambophilous. The natural fruit set does not exceed 15% despite the plant being ambophilous. Scarabaeid beetle by causing flower damage and bruchid beetle by using buds, flowers and fruits for breeding greatly affect fruit set rate and thus the success of sexual reproduction in this plant species is also affected. Seeds are non-dormant, the embryo is chlorophyllous while the fruits are on the plant. Healthy seeds germinate as soon as they reach the forest floor but their establishment is seemingly affected by resource constraints due to the rocky habitat. The study suggests that non-annual flowering, massive flowering for a short period, high bud/flower and fruit infestation rate, absence of seed dormancy and rocky habitat could attribute to the endangered status of S. roxburghii.