AN INVESTIGATION OF SOME PHENOLOGICAL EVENTS IN THREE MANGROVE GENERA WITH REFERENCE TO SELECTED CLIMATIC FACTORS IN NEGOMBO LAGOON

Abstract

Mangroves consist of ICw tree species which are adapted to grow under tidal conditions.Studies on the phenology of mangroves is scarce. The main objective of this research wasto study major phenological cycles of some overexploited species and to compare thesewith previous observations on the same species samples from three other lagoons.

Phenological cycles of leafing. flowering and fruiting of R hizophora apiculata, R.Mucronata, Bru.guicra gvmnorhi:a. B. Sexangula and Ccriops taga! were studies for aperiod of 24 months at selected sites in Negombo lagoon which is located in the wet zoneof Sri Lanka. Phenological cycles were followed and phenological indices were calculated.Thcse d;lla were compared with monthly variations in rain fall. temperature and humidityof the study area.

Leal production showed two distinct maxima per year in all species. Rainfall seemed toexert a great influence on leaf rcflushing. Peaks of leaf rcflushing coincided with lulls ofIluwcriru; and fruiting. Annual bimodality was observed for flowering fruiting in allspecies. These species showed unimodal pattern of some of these events when they weregrowing in dry zone

Phenological cycles constructed using data obtained show no intraspecific variation in thetime required to complete a single flowering-fruiting cycle, Similarly. intragcncricvariation was absent in the life time of leafing cycles

In Rh izophora species. leaf bud jut emerged took I - 1,5 yrs to complete a single cyclewhere as in Bruguicra species this period was 2 - 2,5 yrs, In CeriOI)S tagal, it was 1,5 - 2yrs. Similarly. a flower bud of Rhizophora species took 1,5 - 2.5 yrs, Brugcciera species Iyr and C tagu! about 1,5 yrs to form a mature hypocotyl.

A comparison of these observations with findings of the previous study proves thatphenological cycles in studies species are environmentally dependent and not speciesspecific,

Unimodality of floral phenology in dry zone species may he due to the seasonal variation inground water salinity,