First Insights into the Floristic Community, Faunal and Macro-Fungal Richness of Diyagama Forest, Homagama, Colombo District

Abstract

Urban forest patches provide numerous environmental benefits. Diyagama forest (8.9 ha) is the only forest patch in the suburbs of Homagama which is left aside after recent infrastructure developments. For the first time we describe its biodiversity with special emphasis on floristics. Sampling was conducted in July 2024 for flora and from April-October 2024 for fauna and macro-fungi. Inventories of flora, fauna and macro-fungi were prepared. Ten 100 m² plots were located in pairs in five locations in the forest, and the tree height, diameter at breast height (DBH), and number of individuals in understory were recorded. Plant cover of undergrowth was estimated using Braun – Blanquet scale. Temperature, relative humidity, and light intensity were measured at three random points in each plot. Plant life form was analyzed, ecological dominance of canopy trees was determined using the importance value (IVI). Variations in forest plant community were determined by Bray-Curtis similarity index of hierarchical clustering method using SPSS Statistics. The temperature, relative humidity, and light intensity across all forest plots reported average values of 31.8°C, 80.94%, and 9413.31 lux respectively. The trees reached approximately 10m height in the canopy. Endemism was 12.6% for flora and 11.58% for fauna. The biological richness included 96 plant species belonging to 51 families and 87 genera of which 12.6% were threatened (8 vulnerable and 3 endangered). Only 12 were exotic species. The macro fungal richness was 48. Among the 72 bird species, 5 were threatened species (with 2 critically endangered). Out of 29 reptile species one species was in the threatened category. Amphibian richness included 7 species, while richness of fish species was 15 with 4 being threatened. Butterfly diversity was notable with 52 species, 3 of which are threatened. The site hosts 16 mammal species, including 5 threatened species. The canopy tree density was low (8.7/100m²) whereas the dense understory had 58.6 individuals/100m².  Due to shade undergrowth was scanty but had 36 individuals/100m². The dominant plant life form was trees (80.85%) of DBH range of 33-53cm. Higher IVI values were exhibited by Alstonia macrophylla (51%), Horsfieldia iryaghedhi (39.8%) and Lannea coromandelica (39.3%) reflecting their ecological dominance in the forest community.  Invasive alien shrub and herb species were restricted to forest edges and absent inside. The sample plots separated with<25% dissimilarity indicating an even community structure across the forest.  Nevertheless, it offered a variety of microhabitats for many fauna and macro-fungi.  As a biologically wealthy forest patch at mid-successional stage of regeneration, its conservation efforts should focus on controlling the spread of invasive species, prevention of road kills of fauna, protecting the remaining large trees against illegal exploitation and promoting natural regeneration with least disturbance in order to maximize its ecosystem services.

Keywords: Diyagama Forest, Plant community, Fauna, Macro- fungi