IMPACT OF NUTMEG (Myristica fragrans) DOMINANCE ON VEGETATION COMPOSITION AND DIVERSITY IN KANDYAN HOME GARDENS

Abstract

Kandyan home gardens are well-established land use systems found in the mid country wet zone especially in and around the Kandy District. Due to their unique vegetation characteristics, these ecosystems play an important role in enhancing food security and biodiversity. Among the cultivated species, nutmeg (Myristica fragrans) has become a popular crop due to its high economic value. This study aims to investigate the dominance of nutmeg in Kandyan home gardens and its impact on plant diversity by comparing the species diversity of home gardens with and without nutmeg trees. Vegetation data were collected using the Point-Centered Quarter Method (PCQM) at 10 sampling points along a 50 m transect, recording 40 trees in total. Light intensity at each point was measured and for each plant, the distance from the central point, diameter at breast height (DBH), and tree height were recorded. Species dominance, diversity, and structure were assessed using standard ecological indices. A species abundance matrix within study sites was analyzed using PCORD software. Cluster analysis and Detrended Correspondence Analysis (DCA) were used to determine species composition patterns across Kandyan home gardens. Biodiversity indices were computed using Biodiversity Pro software for comparative analysis between sampling sites. Nutmeg was found in 78% of the sites surveyed, contributing an average of 17% to total tree density and 19.75% to overall basal area, indicating its strong ecological presence. Home gardens with higher nutmeg density showed lower absolute tree density, reduced light intensity, and a strong negative correlation between nutmeg abundance and understory light levels. Species diversity was notably lower in nutmeg-dominated sites. Cluster and DCA analyses grouped home gardens into distinct clusters based on species assemblages, with nutmeg dominated sites forming separate ecological outliers. DCA ordination confirmed that Myristica fragrans strongly influenced site distribution, highlighting its role as a key driver of species composition. These findings suggest that nutmeg dominance can substantially alter species diversity and ecosystem structure in Kandyan home gardens. Adaptive management strategies are recommended to maintain productivity, ecological resilience, and biodiversity conservation in these systems.