Dendrological characteristics and selection criteria for seed mother trees of Xylia xylocarpa (Roxb.) W.Theob. in Yok Don national park

Abstract

This study aimed to identify the dendrological attributes, stand structure, and selection criteria for seed mother trees of Xylia xylocarpa (Roxb.) W.Theob. in Yok Đon National Park, Dak Lak Province, Vietnam. Three line transects (3.1-4.5 km in length) combined with two 50 × 50 m sample plots and surveys of 20 candidate mother trees were employed to evaluate overstory composition, growth characteristics, and natural regeneration. The results indicated that X. xylocarpa is a dominant species in the dry deciduous forest ecosystem, occurring mainly at elevations of 220–270 m, with most sampled stands concentrated between 220 and 260 m on gently sloping terrain characterised by well-drained gray and basalt-derived soils. The species achieved an Importance Value Index (IV%) of 9.9–14.9%, confirming its ecological prominence alongside key associates such as Dipterocarpus obtusifolius, Shorea obtusa, and Lagerstroemia calyculata. Natural regeneration density ranged from 46 to 51 individuals per plot, of which X. xylocarpa accounted for 7-8 seedlings per plot; More than 70% of regenerating individuals were classified as good quality, and seed-origin regeneration was predominant (>75%), indicating a relatively stable regeneration process. Based on the Vietnamese Standard TCVN 8755:2024, 20 seed mother trees were selected, exhibiting superior phenotypic performance with a mean diameter at breast height (DBH) of 32.2 cm, a mean total height of 23.3 m, an average height-to-clear-bole ratio of 66.2%, a mean quality score of 14.4/15, and an average seed yield of 4.7 kg per tree. The findings provide essential quantitative evidence for forest genetic resources conservation, the establishment of seed stands and seed orchards, and the sustainable development of X. xylocarpa to support large-timber reforestation programs in the Central Highlands of Vietnam.