RESULTS OF AN UNDERPLANTING TRIAL WITH TWO NATIVE TREE SPECIES T. javanica AND E. fordii IN Acacia hybrid PROTECTION PLANTATIONS IN QUANG TRI PROVINCE

Abstract

This study was conducted to assess the growth of two native tree species planted under the canopy of Acacia hybrid plantations in Quang Tri province and Hue city. It provides the basic for selecting appropriate species to establish a model of converting monoculture Acacia hybrid plantation forest into mixed native forest in Quang Tri province. The ealier survey had identified eleven native tree species planted under the canopy of plantation forest within the study area. Among these, two species (E. fordii and T. javanica Blume) were selected for underplanting experiment in Acacia hybrid canopies at two different canopy closure levels (0.3 - 0.4 and 0.5 - 0.6, respectively). After 2 years of planting, E. fordii demonstrated a survival rate of 90.4 - 92.3%, while T. javanica showed a lower, rate of 88.0 - 91.3%. Both species showed greater diameter at ground level (D₀₀) and total height (Hvn) growth under the 0.3 - 0.4 canopy closure compared with the 0.5 - 0.6 canopy level. Within the 0.3 - 0.4 canopy condition, E. fordii achieved the average D₀₀ of 1.55 cm and Hvn of 1.35 m, whereas T. javanica recorded as of 1.45 cm 1.25 m, respectively. The chlorophyll a/b ratio < 2.3 indicated that both species exhibit shade tolerance during the early growth stages, with E. fordii showing a higher degree of shade tolerance than that of T. javanica. The findings suggested that maintaining a closure level of 0.3 - 0.4 in the second year would be an appropriate silvicultural measure, facilitating optimal growth of underplanted native species in the process of converting Acacia hybrid plantations into mixed native forests.