Regeneration, Stand Structure and Species Composition of Magnolia lanuginosa (Wall.) Figlar & Noot. Forest in Kengkhar, Bhutan

Abstract

This study aimed to understand the regeneration, stand structure and associated species composition of Magnolia lanuginosa along the altitudinal gradient, assessed its conservation threats and looked into its suitable habitat niche for its growth and development model in the country using ArcGIS. A systematic sampling along the altitudinal gradient with the altitude difference of 100 m as the plot to plot distance was adopted in a natural forest at Nyugphu Goenpa in Kengkhar for data collection. Plot size of 20 x 20 m for trees (DBH ≥ 10 cm and H ≥ 1.3 m), 5 x 5 m for regeneration (DBH < 10 cm and H < 1.3 m) and 2 x 2 m for groundcover were used to collect vegetation data. Soil samples were collected using soil auger from the centre of each plot. A total of 279 plant species under 64 families were recorded from the study area. Hamamelidaceae was found to be the most dominant family in the study area. The associated tree species of M. lanuginosa were Exbucklandia populnea, Quercus glauca, Cinnamomum bejolghota, Macaranga denticulata, Pinus bhutanica, Symplocos racemosa, Quercus lamellosa, Quercus oxyodon, Eurya acuminata and Engelhardia spicata. The study covered slope ranging from 23% to 47% on south and north aspect. The maximum DBH of 115 cm and maximum height of 46 m were recorded. The total basal area of M. lanuginosa was 32,456 cm²/6,000 m² while the stem density was 17 stem/6,000 m². Over extraction and illegal felling were the highest conservation threats known to the species. However, regeneration of M. lanuginosa was minimal in close canopy forest compared to the human disturbed and open areas