Multi-Temporal Canopy Gaps Assessment Using Airborne Laser Scanning Data: The Case of the Protected Forests in the Carpathian Montane Ecosystem in Poland

Canopy gaps are important footprints in understanding the forests’ disturbance regime and regeneration process, yet there is a need to employ multiple metrics along the gradient of time for a deeper understanding of the dynamics. In this study, aerial laser scanning-derived canopy gap data of three protected forests in the Carpathian Mountains, stratified by location and forest types, were examined at temporal and spatial scales. Multiple features were examined, such as gap size structure, gap area proportion, gap geometry, and the relationship between gap geometry and size and gap formation. The results indicated that the gap size frequency has a heavy-tailed right-skewed distribution and mostly maintains the same proportion across time, even after the reduction in gap numbers. Meanwhile, the probability distribution of the gap sizes is not exclusive to the power law; it also follows log-normal and exponential distributions. Gap counts and gap percentages decreased over time, but with the increasing size of gaps. Gap shape complexity was moderate around 2.0, but tended to have a complex shape as the gap size increased. The temporal gap dynamics were characterized by four gap types: recovered or closed gaps, persistent gaps, expanded gaps, or new openings, with the balance influenced by the severity of disturbance. These findings underscore the importance of collective gap metrics across temporal and spatial scales in elucidating gap dynamics of unmanaged forests.