Die-out of Manilkara hexandra from Bundala National Park, Sri Lanka: Causes and some possible underlying mechanisms

Abstract

Bundala National Park (BNP) is a biologically diverse wetland habitat where a sizable area of Tropical Semi-deciduous (TSD) forests of Sri Lanka exists. Manilkara hexandra is the only dominant canopy tree species in these forests. However, the species appears to be dying out from BNP. With the aim of revealing the causes and possible underlying reasons for the die-out of the species, the population size, spatial distribution, natural regeneration and the healthiness of individuals of M. hexandra in BNP were examined in twenty five 50x50 m² plots in three belt transects which were established across different forest categories in BNP. The major alien exotic plants in these plots were also enumerated. Results revealed that the tree die-back and poor natural regeneration were among the major causes for the die-out of M. hexandra from BNP, which had altered the population structure and distribution of the species over space. Live individuals of the species were absent in some degraded sites especially those invaded by Prosopis juliflora. Presence of over-mature cohorts, occurrence of tree cankers and presence of the aggressive invader, P. juliflora appear to affect the die-back of M. hexandra. This study provides a clue that there is a possibility of dying-back of the remaining healthy trees of M. hexandra in TSD forests of BNP in the near future, unless the threats imposed upon M. hexandra are uplifted through strategic management activities.