Abstract: Regeneration characteristics of major tree species are very important to forest regeneration and sustainable management of secondary Pinus tabulaeformis forests in the Ziwu Mountains , Gansu Province .The primary objective of this study was to examine the regeneration patterns of major trees in gaps and non-gaps of a secondary P . tabulaeformis forest .Major trees of the shrub layer in 25 gaps and 25 non-gaps were surveyed and classified into four ecological groups of species according to their importance value (IV).Results of regeneration in gaps showed that Group 1 :six tree species that had a strongly positive response ;Group 2 :two tree species that had a strongly negative response ;Group 3 :eight tree species that had a moderately negative response ;and Group 4 :15 tree species that had no response .For Group 1 the average density and average height of the seedlings in the gaps were superior to those in the non-gaps .For the four ecological groups of species , in gaps and non-gaps there were obvious differences , such as tree density , tree height , the major trees' IV in composition .Regeneration of major trees in gaps was also quicker than non-gaps .Thus , gaps provided favorable growth conditions for regeneration of major trees in secondary P .tabulaeformis forests of the Ziwu Mountains .[ Ch , 2 fig .1 tab .14 ref .]