BIODIVERSITY AND ECOLOGICAL RELATIONSHIPS OF Sindora tonkinensis A. Chev. Ex K. & S. S. Larsen WITH ASSOCIATED TREE SPECIES IN SELECTED FOREST CONDITIONS IN QUANG TRI AND QUANG NAM PROVINCES

Abstract

This study employed standard diversity indices (Shannon, Simpson, and Pielou) to analyze the biodiversity and investigate the ecological relationships of Sindora tonkinensis A. Chev. Ex K. & S. S. Larsen with associated tree species across three distinct forest conditions - broadleaf evergreen and semi - deciduous forests categorized as rich, medium, and poor in Quang Tri and Quang Nam provinces. The results show that the Shannon index ranged from 3.37 to 3.67 in Quang Tri and 3.41 to 3.62 in Quang Nam. The Simpson index remained consistently high at 0.96 to 0.98, while the Pielou index varied from 0.92 to 0.95. These values collectively indicate a relatively stable and uniform community structure, despite variations in species richness among the forest conditions. The number of co - occurring tree species with S. tonkinensis was relatively high (45 - 51 species). However, the occurrence of S. tonkinensis itself was very low, with the species found in only 5 of the 80 observed plots. This represents a sparse 5 - 10% distribution per forest condition, averaging just 6.25% overall. These findings confirm that S. tonkinensis exhibits low gregariousness, with individuals distributed sparsely and independently, significantly challenging its natural regeneration. Associated species classified as "highly frequent" and "frequent", which include Dẻ gai (Quercus macrocalyx), Huỷnh (Tarrietia javanica), Ươi (Scaphium macropodum), Kháo vàng (Machilus bonii), Lim xẹt (Peltophorum dasyrrhachis), Máu chó lá nhỏ (Knema globulifolia), Máu chó lá to (Knema lenta), Chủa (Dacryodes dungii), Săng đen (Diospyros crumenata), Vạng trứng (Endospermum sinensis), Lèo heo (Polyalthia nemoralis), Mít nài (Artocarpus tonkinensis), Trám trắng (Canarium album), Chò đen (Parashorea stellata), Bời lời vàng (Litsea pierrei), Kiền kiền (Hopea pierrei), and Dầu rái (Dipterocarpus alatus). These species are crucial for informing species selection and guiding the design of mixed-species plantation models. Furthermore, S. tonkinensis exhibited superior growth compared to its associated species, confirming its characteristic as a light - demanding species that typically occupies the upper canopy layer. The average distance from an S. tonkinensis tree to its six nearest neighbors ranged from 4.05 to 4.86 meters across the two provinces. Based on these results, the study proposes in-situ conservation strategies, including protecting rich and medium - quality forests, restoring poor forests using appropriate silvicultural measures, and enhancing biodiversity monitoring to ensure the species' long-term survival.