APPLICATIONS OF REMOTE SENSING TO MONITORING FOREST CANOPY DYNAMICS
遥感在林冠动态监测研究中的应用

Canopy dynamics are important in understanding the mechanisms regulating forest production and transition, and maintenance of forest biodiversity. The canopy is the place where important physiological processes such as photosynthesis, respiration, and transpiration occur, and it affects the primary forest production. Canopy dynamics include 3 types of changes: canopy changes caused by insect infestations, diseases, fires, and others; gap dynamics caused by strong winds like typhoons or hurricanes, landslides, floods, volcano eruptions, fires, and other disasters; and the normal changes of tree crowns and the forest canopy. Gradually, the role of remote sensing in detecting, monitoring and assessing forest canopy dynamics has become well established and both the advantages and disadvantages of this approach are widely understood. There are many publications in China and abroad regarding this research field. This paper has reviewed studies in applying remote sensing in the field of canopy dynamics in China and abroad up to the current date. It has looked into the different research emphases that each researcher selected, the methodologies they used, and the advantages and disadvantages involved. It tries to derive some useful suggestions for future research in this field. In summary, the remote sensing data used for canopy dynamics can be divided into two types: one is the satellite remote sensing data such as TM, MSS, and SPOT HRV, the other is aerial remote sensing data. Each of these two kinds of data has its respective advantages and disadvantages. Different data can be used to satisfy different research emphases and different methods and techniques are required accordingly. Satellite data can be used in measuring gap dynamics and canopy changes due to diseases, insects and fires in a large scale. Airborne remote sensing data can be used in monitoring the changes of individual trees, gaps and canopies in a finer scale. In recent years, highly reproducible and consistent orthorectified aerial photographs, in a digital format, have played a very important role in detecting and monitoring changes of tree crowns and the forest canopy. The higher resolution satellite remote sensing data, which will be available soon, would be more suitable for detecting and monitoring canopy dynamics. The existing studies have emphasized the mapping and monitoring of forest canopy, and the mechanism of canopy dynamics will be paid more attention to in the future since such research will provide more in_depth information in modeling the forest growth, forest production, and forest biodiversity.