Abstract: The size structure,disturbance character and forming character of canopy gaps were studied in middle mountain mosit evergreen broadleaf ved forest in Ailao Mountain,Yunnan Province,China.The results showed that the gap size depended on the forming modes of gaps, and the sizes and species of gap maker.The areas of actual gaps was enormously less than the one of extended gaps,and the average of the former was only 33.2% of the latter.The small gaps were main types for the actual and extended gaps.However,the total area of the large gaps was much more than the small gaps.For the actual gaps,the area of the gaps being more than 100～200 m² was about 66 4% of total area. for the extended gaps,the area of the gaps being more than 200～300 m² and 400～500 m² was about 33.1% and 20.6% of the total area. Due to the strong wind in winter, the uproot and snapping were the main types of gap makers,and respectively were 35% and 28% of total number of gap makers. The most gaps were formed of 1～3 gap makers which mostly consited of Castanopsis rufescens,Lithocarpus xylocarpus and Lithocarpus hancei. The three species constituted the 78% of the total gap makers.Under the middle or small scale disturbing, the main arboreal dominant species of upper communicate definitively influenced the gap forming.The distrbution of DBH classes of gap makers mostly varied over 21～40,41～60 and 61～80 cm.The amounts of them were about the 31.6%,20.0% and 18.3% of total amount,respectively. The distribution matched perfectly with the distribution of the gap areas.This indicated that the DHB calsses of the gap makers were closely related to the gap areas.

Key words: Soil organic carbon storage, Soil organic carbon density, China soil database