Fig. 1. Forest distribution map of Heilongjiang Province

Fig. 2. Differences between forest canopy height data and average tree height observations in sample plots

Fig. 3. Accuracy of forest age for different forest types estimated by different models

Fig. 4. Overall validation accuracy of forest age estimated by different models

Fig. 5. Spatial distribution of forest age in Heilongjiang in 2020 using random forest model

Fig. 6. Distribution of forest age data for different forest types in Heilongjiang

Fig. 7. Forest age distribution of Heilongjiang in Shang’s data and differences between it and the data in this study

Fig. 8. Differences between the estimated forest age and Age_shang

Fig. 9. Statistical comparison of two forest age data

Fig. 10. Importance of different factors in a random forest model for estimating forest age