Abstract:

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 denticulata and Millettia leptobotrya forests were 19 182.11, 19 474.81, 19 551.38 and 19 445.95 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 yunnanensis showed 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.

Key words: energy, caloric value, dominant species, secondary succession, Xishuangbanna