Recovery of secondary forests on swidden cultivation fallows in Laos

Species composition, structure and diversity of secondary forests recovered on abandoned swidden cultivation fields in the lowland of Laos were studied in relation to distance from the natural forest, fallow age and crop-fallow rotation cycle. All woody species with stem diameter ≥1 cm were identified, counted and their diameter at breast height (1.3 m, dbh) measured on 290 plots in 162 swidden fallows. Distance from the forest edge related non-linearly and explained 46%, 54%, 63% and 52% of the variation in species richness, stem density, basal area and Simpson's index, respectively. The basal area of secondary forests increased significantly (p < 0.0001) while stem density tended to decrease (0.05 < p < 0.1) with increasing fallow age, whereas species richness and diversity measures remained insensitive. Species richness, stem density, basal area and Shannon-Wiener index were reduced by 28%, 35%, 72% and 23%, respectively while the number of bamboo clumps increased significantly by 45% as the crop-fallow rotation cycle increased from one to three. The occurrence of bamboo had a negative effect on most of the vegetation characteristics analyzed. From forest production and biodiversity conservation viewpoints, it is recommended that the natural regeneration in fallows with a history of previous severe land use intensity should be supplemented with enrichment planting irrespective of its distance from the natural forest. Although the management objectives for secondary forests on swidden fallows are not clearly set, promoting the development of bamboo forests in fallows would be one management option, given its importance in rural livelihood.     

老挝过度采伐热带混合落叶林区的人工补植(英文)

人工补植通常用于增加低商业价值树种盛行的次生林中期望树种的密度。本研究评估了均格种植法(vis-à-vis gap)和行植法(line planting)2种人工补植方法,以及老挝过度采伐的热带混合落叶林中的青皮木(Vatica cinerea) 和龙脑香木(Dipterocarpus alatus)和3种豆科植物(缅茄 Afzeliax ylocarpa,大果紫檀Pterocarpus macrocarpus,酸枝木Dalbergia cochinchinensis)的表现。人工补植实验安捧在了一个随机完整的大块场地,做了7个重复。栽植7年后测定了存活率、高度和直径生长,并进行方差分析。用2种人工补植方法栽植的幼苗的存活率没有发生变化(p0.05)。然而,就直径和高度生长而言,均格种植法要比行植法效果更好。这与林冠在格间和行间块速封闭有关,这种情况在行间更加明显。在存活率,高度和直径生长方面,存在着明显的种间变异。耐阴的龙脑香科树种存活率和生长表现优于喜光树种(p0.0001)。个体的大小分布不规则,说明林下光照条件不均衡。考虑到行植法很难维持恒定线条宽度和均匀光线条件,及其每年用于清理的成本和僵硬的几何模式,我们推荐采用均格种植法。龙脑香木(Diperocarpus alatus)和青皮木(V.cinerea)可用于混合阔叶林人工补植的树种。缅茄、酸枝木和大果紫檀可作为人工林的混合树种,在较宽林隙地、直线区域和开放地种植或在火耕林幼林冠下种植。