Influence of exploitation on population structure, spatial distribution and reproductive success of dioecious species in a fragmented cloud forest in India

Abstract

The population structure of three dioecious species, Diospyros montana, Diospyros sylvatica and Garcinia talbotii was studied in a seasonal cloud forest in the Western Ghats of India. In an undisturbed, natural population of D. montana, female fecundity was not significantly influenced by distance to neighbours or by flower numbers on neighbours. In the same population fruit set was also unrelated to the angular dispersion of neighbours. On the other hand, in an altered population of this species in which conspecifics are extremely isolated due to human activities, insect visitation and fruit set were strongly and negatively correlated with distance to the nearest male. Moreover, the number of insects and fruit set in the natural population were significantly higher in the natural population than in the altered population. In the natural population, trees of large girth produced larger numbers of flowers in both sexes and females which produced larger numbers of flowers, also produced more fruits and fruit set (fruits/flower). In the altered population, fruit numbers and fruit set in female trees were unrelated to the flower numbers, which is possibly due to pollination limitation as a result of inadequate pollinator visits at female trees. Sex ratios were male-biased (3.7:1) in the natural population and female-biased (1:2) in the altered population of D. montana, as well as in G. talbotii (1:3.8) and D. sylvatica (1:12.2) populations where the lower girth classes are mainly cut. The girth class distribution of G. talbotii and D. sylvatica populations was skewed towards larger girths suggesting that future recruitment will be severely affected.