Empirical models for measuring the leaf area and leaf mass across growing periods in broadleaf species with two life histories

Leaf area (LA) and leaf mass (LM) are key parameters for predicting plant growth, but empirical models for measuring LA and LM at the leaf scale in different broadleaf species of saplings and adult trees across growing periods have rarely been proposed. Here, we collected leaf samples from saplings and adult trees of eight temperate broadleaf tree species during three growing periods (i.e., May, July and September) in northeastern China. For each leaf sample, we measured LA, LM and some leaf structure parameters (e.g., leaf length, L, and leaf width, W). We calculated the leaf length: width ratio (L: W). Afterwards, the data from the eight broadleaf tree species were classified into two categories by L: W and then tested to determine whether life history and growing period had a significant influence on developing the empirical models. Finally, we developed combined empirical models for predicting the LA and LM of saplings and adults of different broadleaf tree species across growing periods. The results showed that both life history and growing period generally had a more significant effect on predicting LM than LA for the two L: W categories. Generally, the forecast accuracy of these combined empirical models in predicting the LA and LM of the saplings and adults of most species across growing periods ranged from 83% to 93% and from 76% to 82%, respectively. In addition, the combined empirical models of the saplings or adults were suitable for predicting the LA and LM of six shrub species with maximum forecast accuracies of 93% and 85%, respectively, indicating that our developed combined empirical models were generally effective in predicting LA and LM in other broadleaf species. Furthermore, the optimum number of leaf samples ranged from 11 to 14 for LA and from 59 to 62 for LM, with forecast accuracies all greater than 97% for the broadleaf species.