Enrichment planting in a logged-over tropical mixed deciduous forest of Laos

Abstract

Enrichment planting is commonly used for increasing the density of desired tree species in secondary forests often characterized by a prevalence of low commercial species. The objectives of the study were to identify the optimal enrichment planting method vis-a-vis gap and line planting, and to evaluate the performance of two dipterocarps (Vatica cinerea and Dipterocarpus alatus) and three legumes (Afzelia xylocarpa, Pterocarpus macrocarpus, Dalbergia cochinchinensis) planted in logged-over mixed deciduous forest of Laos. The enrichment planting trial was arranged in a randomized complete block design with seven replications. Survival, height and diameter were measured seven years after planting and subjected to analysis of variance. Survival rate of planted seedlings did not vary between enrichment planting (p > 0.05). However, diameter and height growth was favored more in gaps than in planting lines. This was related to rapid canopy closure in both gaps and lines, albeit more remarkable in planting lines. Significant inter-species variation was detected for survival rate, height and diameter. The shade-tolerant dipterocarps had better survival and growth than the light-demanding leguminous species (p < 0.0001). The size class distribution of individuals was irregular, accentuating uneven light condition in the understory. Given the difficulty to maintain constant line width and even light condition, the cost of annual clean operation and the rigid geometric patterns of planting lines, the use of logged-over gaps for enrichment planting is recommended. Dipterocarpus alatus and V. cinerea are recommended for enrichment planting in mixed deciduous forests. A. xylocarpa, D. cochichinensis and P. macrocarpus can be planted in wider gaps, lines and open sites as plantation of mixed species or under canopy of young swidden forests.