Ecological status of Nageia wallichiana (C. Presl.) kuntze an endangered conifier of western ghats in Mankulam forest division

Abstract

Nageia wallichiana (C.Presl.) Kuntze is a lesser-known rare arborescent, threatened evergreen conifer species of wet evergreen forests of Western Ghats. A study on the distributional status and ecology of this species was conducted in the natural habitats in Mankulam Forest Division. The study aimed at understanding the floristic composition and natural regeneration patterns in the natural habitats of Nageia wallichiana. The additional objective was to assess the physicochemical properties of the soil in the Nageia wallichiana growing areas. The purposive sampling of vegetation was done in 20 x 50 m main plots in Nageia wallichiana growing areas (NG) and control plots were taken in areas without Nageia wallichiana (WNG). The regeneration pattern of trees was studied by taking 5 m x 5 m subplots for saplings and 1 m x 1 m nested plots for seedlings inside the main plots of NG. From NG, a total of 188 individual trees belonging to 67 different species and 28 different families were identified from three different Nageia wallichiana growing patches, viz., Kannadipara, Idathattu, and Kallar. In WNG, 94 individual trees belonging to 46 species and 25 different families were identified. The altitudinal range of occurrence of Nageia wallichiana in the study area was found to be 934 –1463 m above MSL. The girth class distribution of the species showed an L-shaped curve with 90 percent of individuals below 50 cm girth. The floristic studies in the area showed that the natural habitats of Nageia wallichiana harbor a large number of trees in endemic and threatened categories. The typical evergreen species, Cullenia exarillata showed the maximum dominance in NG followed by Mesua ferrea and Bhesa indica. In WNG, the most dominant species were Dysoxylum malabaricum, Vateria indica and Polyalthia fragrans. The comparison of tree diversity between NG and WNG didn’t reveal any significant variations. The ecological distance analysis and clustering showed significant difference in species composition between NG and WNG. The ordination plots proved Bhesa indica as a strong species associate of Nageia wallichiana. The regeneration study showed a lower diversity of regenerating individuals in the study area than mature trees and a difference in species composition was also observed. The analysis of soil properties found that the soils from Nageia wallichiana habitats were higher in moisture content and organic carbon and lower in total nitrogen content. The study didn’t found any relation for soil pH and bulk density on the occurrence of N.wallichiana. The study identified the habitat specialist nature of Nageia wallichiana from the restricted distribution of the species in certain patches of the study area. The occurrence of this only conifer of the Western Ghats in the Mankulam forest Division indicates the importance of the area because Nageia wallichiana is considered as a better indicator of ecological conditions. The study also observed a higher rate of regeneration for this species in the study area indicating the presence of ideal ecological conditions. However, a more focused study considering the disturbance levels in the study area and some extra parameters such as soil depth, soil nutrient contents, frequency of fire occurrence etc. will give a better understanding of the restricted occurrence of this species in the study area and it may contribute in the development of specialized conservation strategies.