Objective The present work aims to explore the variation trends of the heating values of woody plant foliage and its relation to the chemical composition.

Method 27 woody plant species belonging to 20 families including coniferous, broadleaf trees and shrubs, were adopted and the measurements were conducted through the proximate analysis, ultimate analysis and the detection of the heating values.

Result Test results of the leaf samples indicate that their higher heating values on air-dried basis (HHV_d) vary in a broad range from 17.48 to 24.01 MJ·kg^-1, with the average value of 21.16 MJ·kg^-1. The values of the HHV_d are very close for the samples from the same family, and the ash content on air-dried basis plays negligible role in altering the magnitudes of the HHV_d for the species studied. Further analysis indicates that the HHV_d closely relies on the content ratio of volatile matter to the fix carbon (VM_d/FC_d). The ratio of VM_d/FC_d increases with the increase in the atomic O/C ratio of the leaf samples, whereas the content ratios of fix carbon to the combustible substances correspond to the levels of the lignin content stored in plant foliage.

Conclusion The increases in the atomic O/C ratio and atomic H/C ratio imply a decrease in the lignin content stored, which lead to a reduction in a higher heating value on air-dried basis. It is found that the higher heating values of these leaf samples on air-dried basis can be precisely determined by the empirical formulas proposed as the following:HHV_d=0.189 3VM_d+0.369 5FC_d and HHV_d=0.447 8C_d+1.407 2H_d-0.283 7O_d, which provide the basis for quick evaluation of the heating values of the leaf samples on the received basis.