Abstract: Tree regeneration understory and in gaps of an Abies fargesii-Betula utilis mixed forest and the soil chemical properties were investigated in Taibai Mountain, China, and the effects of gaps and the soil chemical properties on tree regeneration were analyzed. The results showed that there was low tree regeneration density in the Abies fargesii-Betula utilis mixed forest (0.059 trees·m^-2), but the regeneration amount of Abies fargesii was dominant no matter in gap or understory. The difference of tree regeneration densities was not significant between understory and in gap (P=0.160), however, the seedling density of Abies fargesii in gap was significantly higher than in understory (P=0.012). Correlation analysis indicated that small gaps were more conducive to the regeneration of Abies fargesii (r=-0.397,P=0.030), while gap size had no significant effect on the regeneration of Betula utilis (r=0.125,P=0.511). In understory, the regeneration density of Betula utilis was significantly positively correlated with soil alkali-hydrolyzable N content, total P content and pH. In gap, the regeneration density of Abies fargesii was significantly negatively correlated with soil total P content and available P content, and the sapling density of Betula utilis was significantly negatively correlated with soil total P. The other soil chemical properties understory (organic matter content, total N content and available P content) and in gaps (pH, organic matter content, total N content and alkali-hydrolyzable N content) had no significant correlation with the regeneration densities of Betula utilis and Abies fargesii. Soil pH was significantly higher in understory than in gaps, whereas organic matter content, total N content, alkali-hydrolyzable N content, total P content and available P content were significantly lower than in gaps.

Key words: tree regeneration, understory, gap, soil chemical properties, Taibai Mountain