Site conditions for regeneration of Hopea odorata in natural evergreen dipterocarp forest in southern Vietnam

Matching species to suitable sites is important in reforestation. This study investigated the site conditions that support regeneration of Hopea odorata, a valuable timber species, in a secondary evergreen natural forest. Stand structure, light intensity at seedling level and soil condition were examined in three representative 50 × 50 m plots. The upper canopy was dominated by four dipterocarps: H. odorata, Shorea roxburghii, Anisoptera costata and Dipterocarpus alatus. The prevailing stand structure supported vigorous germination but not development of seedlings of all four species. Low light levels near the forest floor were the major constraint on seedling development of H. odorata. There was no regeneration when the mean per cent transmitted incident daily photosynthetic active radiation (PAR) was 2.2%; seedling germination but not development was supported when PAR was 6.6%; regeneration and development occurred when PAR was 11.4%. The soils were slightly acidic with low clay and high sand contents and low nutrient concentration, but this was apparently not a constraint on growth given adequate light conditions. The results suggest that the re-establishment of H. odorata on degraded sites using nurse crops should be possible provided that high levels of shading are avoided.