The floristic richness of a small agricultural holding in an urbanizing landscape: A case study of Mannankulam Estate, Eastern Coastal Sri Lanka

Agricultural lands are often undervalued as potential refuges for biodiversity. This study aimed to (i) document the floristic diversity of Mannankulam Estate in Akkaraipattu, Ampara District, Eastern Province, Sri Lanka, (ii) assess the conservation status of indigenous and threatened plant species, and (iii) evaluate the role of regenerative agriculture and habitat heterogeneity in supporting biodiversity. The 12.5 ha estate, surrounded by the urban sprawl of Akkaraipattu town, is a remnant of former extensive coconut plantations and rice fields, partially converted to residential and commercial use over the last four decades. The estate comprises 32% coconut plantation, 32% plantation edge with natural regeneration, 27% rice fields, and 9% lagoon edge with natural vegetation, has practiced regenerative agriculture since 2009 and certified as organic. Over a three-year period (2021–2023), 227 plant species belonging to 179 genera and 63 families were recorded. Indigenous flora accounted for 78.4% of species, including the endemic shrub Jeffreycia zeylanica. Seventeen species (9.6% of indigenous flora) are listed as Threatened or Near Threatened in the National Red List, including 2 Critically Endangered, 3 Endangered, 6 Vulnerable, and 6 Near Threatened species. Notably, populations of the endangered woody climber Argyreia elliptica and the epiphytic orchid Vanda tessellata were substantial. Floristic richness was supported by regenerative cultivation practices, habitat heterogeneity with 41% semi-natural and natural areas, living fences, 1000 coconut trees, and several large old trees. The structural and trophic complexity provided by fruiting trees, herbaceous and woody flowering species, and rice fields attracted frugivorous and granivorous birds, insect and avian pollinators, butterflies and caterpillars. This study demonstrates the potential of small, privately owned agricultural holdings to serve as vital biodiversity refuges, particularly in regions undergoing rapid urbanization.