Abstract:
Urban wetlands are vital ecosystems that play a significant role in ecological stability and
urban sustainability. The Beddagana Wetland Sanctuary, a Ramsar site in Sri
Jayawardenapura Kotte, Sri Lanka, provides important services such as enhancing
biodiversity, flood mitigation, water purification, and climate regulation. This study
surveyed the vegetation structure, and species composition in the sanctuary using a plot-
based sampling method. A total of six 10 m × 10 m plots were established randomly across
representative habitat types within the study area. In each plot, overstory vegetation with a
girth at breast height (GBH) of ≥10 cm was measured using a measuring tape and height was
recorded using a laser rangefinder. Understory vegetation (individuals <10 cm GBH and
above 1 m height) was measured within the same plots by counting the number of individuals
per species. A total of 25 plant species belonging to 23 genera and 19 families were recorded
across six plots. Of them, 19 were tree species followed by five shrubs, and one herbaceous
species. Syzygium caryophyllatum was the most dominant species (Important Value Index
IVI = 66), with high relative density but low average girth (18.5 cm ± 10.4), indicating strong
regeneration potential. Pongamia pinnata had the highest average girth (89.5 cm ± 10.4) and
contributed 27% to the basal area, highlighting its role as a key canopy species. Several mid-
dominant species such as Macaranga peltata, Cinnamomum verum, and Mangifera
zeylanica reflect succession processes. A reverse J-shaped girth distribution suggests active
recruitment and forest regeneration, characteristic of a dynamic, multi-layered tropical
wetland forest in transition. These findings emphasize the ecological resilience of the
Beddagana Wetland Sanctuary and its critical contribution in supporting urban biodiversity
and ecosystem services. To ensure the long-term health of this vital urban wetland,
continuous monitoring and management are necessary to control invasive species and
enhance its sustainability.
