Predicting the Future Age Distribution of Conifer and Broad-Leaved Trees Based on Survival Analysis: A Case Study on Natural Forests in Northern Japan

Predicting future stand conditions based on tree age is crucial for natural forest management. The objective of this study was to model and predict the future age distribution of Picea jezoensis, Abies sachalinensis, and broad-leaved trees by assessing the past and current survival trends of preserved stands located at the University of Tokyo Hokkaido Forests (UTHF), Furano, Japan. This study analyzed forest census data of four plots (927 trees) in a preserved permanent area over 30 years (1989-2019). Individual tree-ring data were identified using a resistograph to determine the current tree age of the targeted trees. The predicted age distributions nearly converged to the shape of the survival probability curve. Among the scenario predictions, the multimodal age class distribution of P. jezoensis was predominant among all prediction scenarios. In contrast, the exponential shape of A sachalinensis and the age distribution of broad-leaved trees in the 100% scenario gradually shifted to the multimodal shape at the 50% scenario prediction. The species composition of conifer and broad-leaved trees and their age distribution would reach stable states in the long run by reaching a climax state. Therefore, it is theoretically possible to maintain stands under the pre-climax stage by allowing high growth rates at the stand level. The suggested age class-prediction of living and dead trees can improve the natural forest management of UTHF.