Monitoring canopy recovery in a subtropical forest following a huge ice storm using hemispherical photography.

We estimated canopy structure and transmitted radiation using hemispherical photography in four monitoring years (2008-2010, 2016) following the 2008 huge ice storm in a subtropical forest in south China, so as to assess changes in canopy biophysical parameters during forest recovery from natural disturbance. Significant decrease in canopy openness (CO), transmitted direct radiation (TransDir), and transmitted diffuse radiation (TransDif), as well as significant increase in leaf area index (LAI), were found in the disturbed forest stand in the subsequent years following the ice storm, indicating rapid canopy recovery. In contrast, these biophysical parameters of the undisturbed forest stand were quite stable during the monitoring years. The strength of relationships between CO and other canopy biophysical parameters decreased in the disturbed stand along the monitoring years. The disturbed stand had common slopes for the CO-TransDir and CO-TransDif models in the first two monitoring years, but different slopes for the CO-LAI model between the first and the subsequent monitoring years, while the undisturbed stand had common slopes for all the regression models in the first three monitoring years following the huge ice storm. These results showed that stronger correlations of LAI or TransDir with CO were characteristic of less complex canopies, such as those damaged by disturbance; the sensitivity of transmitted radiation in response to CO decreased with canopy recovery. Our findings demonstrated that forests with different canopy structure varied in biophysical parameters, which can be quantified by hemispherical photography.