Abstract:
Detailed overstorey and understorey floristic structure and floristic composition of an upper
montane rain forest, Thotupolakanda was investigated during this study. Due to floristic
heterogeneity, vegetation was studied in the following strata; lower elevation (2200 m –
2270 m), middle elevation (2270 m - 2340 m) and higher elevation (above 2340 m) with
stratified random sampling method. Vegetation structure was surveyed with vertical
distribution, girth class distribution and life form distribution with 31 plots, each 10 m × 10
m in size. Plant species higher than 1 m and gbh greater or equal to 10 cm were considered
as overstorey vegetation. The remaining plants in the understorey vegetation was sampled
with two randomly selected sub plots (1 m × 1 m) in each main plot. The floristic richness
and endemics were also studied. The identity of the collected plant specimens were
confirmed with the National Herbarium, Peradeniya.
During the study 1824 individuals were enumerated and 108 species of 64 genera
belonging to 39 families were revealed. The overstorey consisted of 42 plant species and
understorey consisted of 66 plant species. Poorly distinct two strata were recognized in the
lower elevation as canopy (6 m –12 m) and sub canopy (1 m – 5 m). No clear stratification
was distinct at higher altitude and draft vegetation was recognized from the middle
elevation. Girth class distribution of stems showed the typical reverse “J” shaped curve with
girth of most of the individuals within 11 cm – 20 cm at each elevation level while very few
individuals attained girth more than 70 cm. Both plant height and gbh decreased with
increasing altitude. Life forms recorded in the overstorey were trees and shrubs while
herbs, shrubs, epiphytes and climbers were in the understorey. The prominent life form in
the overstorey and understorey was trees and shrubs respectively.
Compared to the species richness in the overstorey vegetation, higher species richness
was recorded in the understorey vegetation. The highest understorey species richness was
recorded in the middle elevation. Of the total recorded plant species 48% are endemic to
Sri Lanka. The overstorey comprises 67% and understorey comprises 46% endemic
species. Critically endangered possibly extinct endemic plant species Hedyotis
quinquinervia (Rubiaceae) was rediscovered after 107 years in Sri Lanka during this study.
Keywords: Floristic composition, floristic structure, overstorey, Thotupolakanda
