Leaf size, as one of the easier measured plant morphological traits, reflects response and adaptation of plants to environment and indicates functions and processes of ecosystem. When measuring leaf size (the leaf area, LA) in the field, the number of leaves picked off, accepted through common practice, is usually 10-20. However, what the optimal number of leaves is remains unknown. In this study, we attempt to determine how many leaves should be investigated when the leaf size of a tree is measured. The study selected two dominant tree species (Schima superba, Ss and Liquidambar formosana, Lf) from a broadleaved evergreen and deciduous mixed forest in Jinhua Mountain of Zhejiang Province, eastern China. On the basis of a large amounts of sampling (>2500 leaves for each tree) in five diameter of breast height (DBH) classes of tree species and at six directions for each individual, variations of LA in two tree species are statistically analyzed. The optimal number of leaves can be able to mostly represent the common leaf size feature is further investigated.
Results/Conclusions
Mean LA of the evergreen tree Ss is smaller than that of the deciduous tree Lf. The former is 41.60±10.88 cm2 (16.74-100.80 cm2) and the latter 57.65±19.35 cm2 (11.31-129.51 cm2), respectively. LA of Ss is not, but LA of Lf is significantly related to the DBH. LAs of both trees in the middle DBH class (15-20cm) are not significantly different from their means. LAs of two trees have no significant correlations with the sampling directions, but LAs at the east, west and bottom have no significant relationships with their means. Considering the representativeness and practicality in the field sampling, the priority of selecting leaves can target the bottom direction of middle diameter mature trees. Random sampling analysis indicated that, the optimal number of leavea for tree LA measurement is species dependent. The optimal number of leaves for Ss is 40 and for Lf is 170, respectively. Therefore, the optimal sampling number of leaves when measuring leaf area should not be limited to 10-20 leaves. Under sufficient power of labor, material and time, it should measure more leaves.