Phenological responses of four shorea species in Sinharaja rain forest to climatic factors

Abstract

The genus Shorea of the family Dipterocarpaceae represents tall canopy trees that dominate the Sinharaja rain forest. All the species in the genus are endemic to Sri Lanka.

Information on the frequency, duration and intensity of flushing, flowering or fruiting can be obtained from phenological studies. Phenological data are also important to determine the migratory pattern of animals, seasonality in animal reproduction and causes of animal population fluctuations. They can also be used to select trees with desirable characters such as early flowering or heavy fruiting for propagation purposes.

The phenology of four Shorea species (S. congestiflora and S. cffinis of the Thinia group; S. cordifolia and S. megistophylla of the Beraliya group) was studied to understand the differences in flowering and fruiting between the Thiniya and Beraliya group of species and to examine whether there is a variation in their phenological patterns in relation to El-Nino years and non El-Nino years.

The investigation, conducted in the Sinharaja MAB reserve, used marked individuals of the study species growing along the main logging roads. The crowns of the selected individuals were observed using a pair of binoculars at fort-nightly intervals. The daily rainfall and maximum and minimum temperatures recorded were used in this study.

Shorea offinis and S. congestiflora showed regular flowering, blooming every year. Shorea cordifolia and S. megistophyl/a did not flower annually and their flowering was associated with EI-Nino years. Shorea affinis, S. cordifolia and S. megistophylla always bloomed between December - June, mostly in March, while that of S. congestiflora was between August to January, mostly in November. During an El-Nino year, dry season rain fall or wet season irradiance or both can occur. During 1987, 1991 and 1992, the climate data shows that wet season irradiance occurred. The mean annual rainfall of the non EI-Nino and EI- Nino years was 5240 rom and 4710 mm respectively. It may be suggested that the high production of flowering and fruiting of the Beraliya species was associated with the high light levels and drought during the EI-Nino periods.