Abstract:Typical sampling method was conducted to select typical forest gaps of different size, each typical forest gap contained 3 repeats, and the Pinus tabulaeformis seedlings from different size gaps in artificial P. tabulaeformis plantation of Huanglong mountain in Shaanxi province were selected as the research objects. The research was aimed at surveying the effects of forest gap size on branch architecture, leaves characteristics and their vertical distribution, and exploring the adaptation and architecture of P. tabulaeformis seedlings to different size forest. The results showed significant differences in the aboveground architecture and growth of P. tabulaeformis seedlings in different size gaps. (1)Gap size was positively related to caliper, seedling height, crown length and crown area. (2)With the increase of forest gap size, the stepwise bifurcation and interval between branch, while the total bifurcation ratio was declined.(3) The gap size was contrary correlated with needle length and width, but with the increased with needle lengthwidth ratio, total needle area and average needle number. (4)The needles in CK were mostly distributed in below middle part of seedlings, whereas the seedlings in forest gap were mostly distributed in above middle part of seedlings. (5) With the increase of forest gap size, the needle number and relative total needle number of whorled branch in same year increased. In order to promote the regeneration of P. tabulaeformis seedlings, cultivate high quality wood, and improve the stand quality, we should adopted appropriate thinning techniques in the future.