Table 5 The comparison of methods for gap age estimation
Method | Theory | Materials | Advantage | Disadvantage | References |
|---|---|---|---|---|---|
Whorl counts | Treat the saplings age as gap age | Saplings within gap | Quick, simple | Low precision and accuracy | |
The degree of decomposition | With large gap age, comes high decay degrees for gap maker | Gap maker | Quick, simple | Subjective, accuracy decrease with gap age increasing | |
Remote sensing | When the patch changes from forest in image of t1 to gap in image of t2, the gap formed during t1 to t2 | Multi-temporal images | High precision and accuracy | Limited by the spatial and temporal resolution of images, not applicable to gap individual | |
Tree-ring width analyses | The gap-surrounding trees would experience growth release in ring width when the gap formed | Rings of gap-surrounding trees | High precision | The accuracy is limited in the mixed secondary forest | York et al. 2010; Soliz-Gamboa et al. 2012; Cartera et al. 2021 |
Stable carbon isotope | ∆13C in tree rings would decrease after gap formation | Rings of gap-surrounding trees | High sensitiveness | Cannot distinguish gap formation and other small-scale damages, high time and economic cost | |
Tree-ring width in combination with ∆13C | First determine the rough time range of gap age by tree-ring analyses and then estimate the accurate time of gap formation by analyzing the ∆13C during the time range | Rings of gap-surrounding trees | High precision and accuracy | Need further verification in other regions | Our study |