Gross calorific value (GCV) has been introduced to biological research and applied to reflect the capability of plant species to fix solar radiation. Calorific value has also been considered as a coefficient characteristic to evaluate the adaptation strategies of plant species to the external environment. Therefore, understanding the variation in GCV among different ecosystems may provide a basis for assessing energy fixation, transformation, and utilization efficiency. A number of studies have indicated that GCV varies among different geographical locations and ecological categories. Some studies have suggested that the energy contents of alpine plants should be higher than those of tropical plants, and have also shown that energy content differs among different plant life forms, decreasing in the sequence tree > shrub > herb. However, little has been reported on the patterns of GCV in different typical ecosystems (at the levels of species, life form, and community) across multiple zones. In this study, we compared the leaf calorific values of plant species in two forest ecosystem-subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests in China. Field sampling was carried out in early August 2013 at Jiulian Mountain (Jiangxi Province) and Dongling Mountain (Beijing Province), China. Leaf samples of 276 plant species were collected from subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests, and the calorific values of these leaves were measured using a PARR 1281 oxygen bomb calorimeter. To explore the variability in GCV, we analyzed the data at the levels of species, life form (trees, shrubs, and herbs), and community in the two forest types. Furthermore, trees were subdivided into evergreen and deciduous, and coniferous and broad-leaved. The results showed that the GCV of the subtropical evergreen broad-leaved forest was 17.83 kJ/g (n=191), whereas that of the warm temperate deciduous broad-leaved forest was 17.21 kJ/g (n=85). The changing trends in GCV among the different life forms were similar in both forests. The sequence of GCV in the subtropical evergreen broad-leaved forest was tree (19.09 kJ/g) > shrub (17.87 kJ/g) > herb (16.65 kJ/g), while the sequence in the warm temperate deciduous broad-leaved forest was tree (18.41 kJ/g) > shrub (17.94 kJ/g) > herb (16.53 kJ/g). Moreover, in both forest types, we found that the GCV values decreased in the following order: evergreen trees > deciduous trees and coniferous trees > broad-leaved trees in the both forests. The average GCV for deciduous broad-leaved trees was larger in the subtropical forests than in the warm temperate forests, whereas the GCV values of evergreen coniferous trees showed the opposite trend. In addition, the leaf calorific values of four coniferous trees in both forests were: Larix principis-rupprechtii (19.32 kJ/g, warm temperate deciduous broad-leaved forest) < Cunninghamia lanceolata (19.40 kJ/g, subtropical evergreen broad-leaved forest) < Pinus massoniana (19.82 kJ/g, subtropical evergreen broad-leaved forest) < P. tabuliformis (20.95 kJ/g, warm temperate deciduous broad-leaved forest). The findings of this study demonstrate the preliminary characteristics of GCV in subtropical evergreen broad-leaved and warm temperate deciduous broad-leaved forests, and also provide new insights about the energy cycles of forest ecosystems and the adaption strategies of plant species to environmental changes.