Forest gap is a driving force for regeneration and succesion of forest ecosystem. The concept was put foward 70 years ago and It has been defined qualitatively: Forest gap is discontinuours gaps formed since tree death or other reasons in the forest.
Literature survey revealed that the gap might be as big as 2 hectars or as smallest as 4 m2. Based on this fuzzy definition, it is hard to make coparisons among various research work. Especialy, as to the decision makers - morden forest manager , it is hard to simulate the natural forest gap process in their practice.
To solve this problem, Prof Jiaojun Zhu and his group in our institute proposed size limitations of the concept acording to the tree shadow length on forest flour The mid day(12:00) shadowlength is taken as the minimum diameter of forest gap (Fig 1) and the shadow length when the daily irradiance reachs the photosynthesis saturated point for light-demanding tree species in the morning is taken as the maximum gap diameter.(Fig. 2). The ratio of everage gap diameter /everage tree height(D/H) is taken as an index to discribe relative gap size. For the temperate forest, zone,for example, when 0.49 <D/H≦1.0,the gap defined as small, when the ratio is 1.0< D/H≦2.0, it is a middle gap and when 2.0<D/H≦3.5 the gap is seen as big. Acording to this definition, any gap that with D/H <0.49 or D/H > 3,5 should not be taken into acount as forest gap. This definition is easily operated and may be used in practice by morden forest managers.
The work was published in Agricultural Land Meteorology, 213 (2015) 64-76.
Zhu JJ, Zhang GQ, Wang GG, Yan QL, Lu DL,Li XF and Zheng X. 2015. On the size of forest gaps: Can their lower and upper limits be objectively defined? Agricultural and Forest Meteorology, 213: 64–76, DOI: 10.1016/j.agrformet.2015.06.015.
