Regeneration in inland lowland forests in south vietnam one decade after aerial spraying by agent orange as a defoliant
Bois et Forets des Tropiques 211: 19-34
ISSN/ISBN: 0006-579X Accession: 006282338
In January 1983, lowland evergreen forests in southern Viet-Nam, for which aerial photographic and chemical spraying records were available, were visited to evaluate residual effects one decade after spraying had ceased. The direct effects of chemical defoliants on forests were immediate, and the chemicals responsible for defoliation do not persist in the ecosystem. The resultant damage varied greatly in intensity. In the majority only the canopy was destroyed, and regeneration existing below has survived to form a new stand. In substantial areas of the two forests examined, though, all but a few tree species were killed. In these areas burning, presumably man-induced, ensued and continues to occur annually in accessible areas, arresting woody succession and leading to semi-stable secondary savannas. The spatial pattern of damage resulting as a direct effect of defoliation is therefore generally no longer discernible. Two principal inland dry land climax forest formation occur in the seasonal lowlands of South Viet-Nam, both generally dominated by the important timber family Dipterocarpaceae. The predominant is a seasonal evergreen forest, which is fire-sensitive; but in drier, western areas fire-climax savanna woodlands occur. In the savanna woodlands many trees, following spraying, sprouted from the butt, or higher on the trunk. It is concluded that all forests effected will take long to recover through natural regeneration, and that the main consequence of defoliation has been to facilitate the penetration of secondary savanna into the evergreen zone. Substantial investment in research and development of plantation forestry is recommended.