| Pinus yunnanensis, one of dominant species in In the mountainous area of southwestern Sichuan province, is a pioneer species and timber tree for quasi-wet broad-leaved forest. Current studies about Pinus yunnanensis mainly focus on the forest management, and little on the relation of gap characters and Pinus yunnanensis regeneration in the Pinus yunnanensis forest. Study on gap regeneration is benefit for us to realize the process of Pinus yunnanensis forest cycle and evaluate the capability of nature Pinus yunnanens forest in regeneration and sustaining. Therefore, the gap characteristics of Pinus yunnanensis forest gap and its regeneration, in Dahei mountain forest park, panzhihua city, Sichuan province, were studied. The factors influencing gap regeneration were further analyzed. Result were as follows:(1) There was an ellipse shape in gap and the proportion of long and short axes was 1.8 in the canopy gap (CG) and 1.5 in the expand gap (EG). Gap area was mainly below 500m2, and averaged as 255.6±195.7 m~2 ranging from 18.1 to 934.5 m~2 in CG, and as 458.9±272 m~2 from 50.7 to 1356.5 m~2 in EG. Gap size depended on the community environments before the gap formation, and the taller, bigger and more numerous gap boundary trees and gap makers produced bigger gaps. There was averagely 2.64 gap makers in each gap (from 1 to 10, and 8 was in short), and half of the gap maker came from wind treefall, 1/4 from standing death and artificial cutting respectively. On the basis of field survey, there were seven gap formation modes: wind treefall (WT), standing death (SD), artificial cutting (AC), WT, WT+ AC, SD+ AC and WT+ AC + SD, and each gap maker could produce 118 m2 CG and 219 m2 EG. The features of gap makers showed as follows: 17.6±2.8 m (averagely and from 11.5 to 24.9 m)in height, 89.3±24.7 a(from 15 to 140 a)in age, and 35.6±7.5cm(from 18 to 64 cm) in DBH. Through the coefficient analysis, we found that gap size did not affected by gap shape, but affected by the characteristics of gap makers and border trees. There were bigger gap makers and border trees, the older community age, and the larger gap size in Pinus yunnanensis forest. On the account of the sustainable management for forests, we should use the gap maker with reason, and selectively and corporately cut the timber, cultivate and manage natural forests according to the rules of nature disturbance for Pinus yunnanensis forest.(2) In Pinus yunnanensis forest, the most GBTs were Pinus yunnanensis and there were mainly 5～9 GBTs per gap (75%);The average height of GBTs per gap was mainly form 18 to 22m (61 %), and the average diameter at breast height was mainly form 35 to 50 cm (82%); The GBTs' crow inclination are obvious, and RCI-1 was greater than 0.5, the average RCI-1 of GBTs per gap was mainly form 0.6 to 0.8 (75 %); The size of GBTs increased with the area of gaps.(3) Crown inclination is consequences that the biological and its environmental factor synthetically influence the crown structure. In the border trees of Pinus yunnanensis gaps in the mountain area of southwest Sichuan, the crown inclination phenomenon, and whether the distribution of neighborhood trees influenced the degree of crown inclination were investigated in this paper. The crown inclination phenomenon was a general feature in the border tree of Pinus yunnanensis, the individual amounts of degree of crown inclination bigger than 0.5 reached 95% [crown inclination 1 (shorted as RCI-1), averaged as 0.72±0.14 (n=291,0.231～1 )]and 93%[RCI-2, averaged as 0.86±0.37(n=291, 0.134～2.583)]. In the especially location studied, the orientation of crow inclination probably related to azimuth, and there were near 80% border trees that were west orientation including southwest and northwest. The RCI-1 significantly related to DBH, lateral tree intervals, back tree intervals, but not to height and low branch height of border trees; the RCI-2 was only obviously correlated with lateral tree intervals, not with DBH, height, low branch height, back tree intervals. Summarily, distribution of neighborhood tree mainly influenced the degree of crown inclination, and probably its size as well in the border trees of Pinus yunnanensis gaps.(4) Three competition indices were used to analyze the neighborhood competition between the standing death tree and living tree, which are in the same DBH. Compartmentalize neighborhood around objective tree in 8m into three types: Pinus yunnanensis,Fagaceaea and other trees. The result shows that, around standing death tree, Pinus yunnanensis,Fagaceaea and other trees individual numbers account different for 42.83 %, 20.65 % and 36.52 % of all individual numbers. Around living tree. Pinus yunnanensis, Fagaceaea and other trees individual numbers account different for 44.29%,22.49% and 33.22% of all individual numbers. For standing death tree, Intra-specific competition and Inter-specific competition are similitude (p>0.05). For living tree, Intra-specific competition> Inter-specific competition(p<0.05) . The competition effects for standing death tree is larger than that for living tree, but the diversity of them is not marked (p>0.05) .Meanwhile, the size of standing death tree have stop growing, but the growth of Neighborhood will release. So, the competition indices, when the tree died, would be lower than which we account. Base on the two points, competitive effect leading standing death tree up to die is not fact. Weiner index,Hegyi index and Zhang Yuexi index are different model, but the results are accord when using the three competitive index for analyzing the neighborhood competition between the standing death tree and living tree.(5) By analyzing effects of gap properties, including gap size, gap age, canopy openness, on the regeneration of Pinus yunnanensis forests in the mountainous area of southwestern Sichuan, the characteristics of regeneration in gap of P. yunnanensis forests were approached. The results showed as follows: 1) there was a higher density of seedlings in smaller gaps, but a higher density of saplings and mature trees in large gaps; 2) there was a higher density of seedlings and saplings in young gaps, and a higher densities of mature trees in mature gaps; 3) with the increasing of canopy openness, density of seedlings decreased, but density of saplings and mature trees increased, and until canopy openness was lower than 0.6, there was no regeneration in gap of P.yunnanensis forests; 4) the transition rate of seedlings to saplings was lower in small gap, young gap and 0.4-0.6 of canopy openness. 5) the importance value of P. yunnanensis listed the first both in gaps and non-gap, indicating the forest in this area will be mainly composed with P. yunnanensis in the future.
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