A Test of Janzen-Connell Hypothesis in Indian Deciduous Forest

Almost 4 decades ago Janzen(1970) and Connell(1971) proposed that one of the key factors in maintaining high tropical tree species diversity was played by the various host-specific seed and seedling predators, herbivores and pathogens. They predicted inexplicably high mortality of seed and seedlings close to the parent tree because of these natural enemies. In the present paper, the primary motive was to identify the spatial patterns of the dispersed seedlings, about four years old and subsequent infection by fungal pathogens, which determine their recruitment, relative to the distance from the parent tree. The field experiment was carried out in the dry deciduous part (50 Hectare plot) of the Mudumalai Tiger Reserve, Tamil Nadu, which confirmed that there is both a decrease in the seedling density and in the proportion of infected seedlings, as a function of distance from the parent tree, among the seedlings of Syzygium cumini, a bird-dispersed tree species. This supported Janzen¿s hypothesis that pathogen activity and seedling vulnerability to disease is maximum, when established near parent tree where seedling density is highest.