该文对西双版纳的4种次生植物群落优势树种的热值进行了研究。4种群落类型分别是山黄麻(Trema orientalis)群落、白背桐(Mallotus paniculatus)群落、中平树(Macaranga denticulata)群落和思茅崖豆(Millettia leptobotrya)群落，群落年龄分别为2、4、6年和大于15年。4种群落各优势树种的平均干重热值分别为19182.11、19474.81、19551.38和19445.95 J•g-1。总体来讲，热值随着群落年龄的增加而增加。增长的原因应该是群落光能利用效率的增加。思茅崖豆群落的热值稍有降低，是因为这个群落样地处在阴坡，不能接受到像其它3个群落那样在阳坡的充足光照。先锋树种的热值明显低于顶极树种。可能是因为在群落演替初期，生态系统增加能量耗散的主要方式是通过生物量的增加；而当结构建成，生物量增加到一定程度，已经没有足够增长空间的时候，生态系统将会改变能量储存方式，主要通过单位质量固定能量的增加，也就是热值的增加，来耗散能量。山黄麻群落中叶片的热值非常低，低于根的热值水平，是短命树种将能量更多地投资于繁殖的原因。
Aims The objective of this study is to determine the allocation pattern of caloric values in dominant species of the secondary forests that developed from deforestation of tropical rain forests in Xishuangbanna, Southwest China.
Methods We studied three 20 m × 20 m plots in each of four communities : Trema orientalis forest, Mallotus paniculatus forest,Macaranga denticulata forest and Millettia leptobotrya forest, which were 2, 4, 6 and >15 years old. We recorded the species name and DBH of all trees with a diameter >3 cm. Caloric values of 17 dominant tree species were determined using five sample trees of each dominant species: one small tree, three intermediate and one large tree. The sampled parts were leaves, branches, stems and roots. The caloric values of three replications for each sample part were measured with a SDACM-IIIa oxygen bomb calorimeter, with an error less than 100 J•g-1. Differences were tested by t-tests.
Important findings The mean caloric values of T. orientalis, Mallotus paniculatus, Macarange denticulataand Millettia leptobotryaforests were 19182.11, 19474.81, 19551.38 and 19445.95 J•g-1, respectively. Generally speaking, the caloric values of the climax tree species were greater than those of the pioneer. Differences between leaves were significant, but differences between branches, stems, roots and the average were not significant. The caloric values of different parts were ranked as: leaves > stems or branches > roots at the average level, although T. orientalis, Vitex quinata and Aporusa yunnanensisshowed lower caloric value in leaves. Results suggest that there was an increase in the utilization efficiency of energy with aging of forests. Ecosystems develop by systematically increasing their ability to convert incoming solar energy; therefore, the transformation efficiency of energy was higher in climax trees than the pioneers. We postulated that in the early succession, ecosystems increase the absorption of energy though biomass accumulation; therefore, pioneer trees show lower caloric values. Along with build-up of organic structure, however, ecosystems augment the fixation of the energy quality, and then caloric values can be enhanced per unit weight.