AN INVESTIGATION OF PHENOLOGICAL EVENTS IN SOME ENDEMIC TREE SPECIES OF SRI LANKA, WITH REFERENCE TO CLIMATE

Abstract

Thirteen endemic tree species were selected for the study from Kottawa Forest Reserve(6.06 N, 80.18E) and Ellakanda Forest Reserve (5.59 N, 80.36E), both of which aresituated in the Southern Province of Sri Lanka. The Southern Province lies in the lowcountry wet zone of Sri Lanka in between the isohytes of 2000 & 2500 mm and is withinthe agroecological region WL 4 where the 75% expectancy value of annual rainfall is>1525 mm. Tropical lowland rain forests dominate both reserves and humid warm climateprevails. Kottawa reserve receives an average annual rainfall of 3700 mm distributedthroughout the year with 2 maxima in April-May and in October-November whileEllekanda receives an average annual rainfall of about 2000 mm with the main rainyseasons from April to June and October to November. The average temperature is around26° C. Phenological events such as leaf growth/greening, leaf fall, flowering, seedripening/fruiting. growth periods, increment growth per month etc. were monitoredmonthly for a period of one year.

It was observed that most phenological events do occur either during the rainy months orare triggered by the onset of rains. All investigated tree species within the reservesexhibited two prominent growth periods per year except for Dipterocarpus zeylanicus,Doona congestiflora and Carallea calycina which showed only one major growth periodper year. All species except for Doona congestiflora, Palaquium rubiginosum andCarallia calycina showed at least some growth throughout the year. The leaf growth inmost species was during the S. W. monsoon period or during the intermonsoon period fromSeptember to November. In the case of Mastixia tetrandra the leaf growth was duringJuly/August. None of the investigated species showed seasonal leaf fall. Flowering wasconfined in most species to the driest months of the year, JanuarylMarch or toAugust/September. Only some species showed two flowering periods per year such asDipterocarpus zeylanicus and Mangifera zeylanica.