| Tilia amurensis is an important broadleaf tree species in mixed broadleaved-Korean forests in Northeast China. To better understand its competition characters in natural forest, basic tree characters were measured in a4ha permanent study plot. And the above-and belowground biomass allocation pattern and crown structure of Tilia amurensis was analyzed using39harvested trees with different diameters at the breast height and different competition intensity. Allometric equations for different biomass components were developed by stem diameters (DBH; tree base, DB;30cm height, D30and1m height, D100). Our main results show that:(1) There was quite difference between intraspecies competition and interspecies competition of Tilia amurensis within different diameter classes in the broadleaved-Korean forest in Jiaohe, Jilin. Competition intensity reached the apex when the diameter was in the20-30cm class. Intraspecies competition intensity was less than interspecies competition intensity. Among all competitors, Ulmus japonica, Acer mono and Fraxinus mandshurica had the most intense competition intensity. The diameter showed a significant power relationship with the stand competition intensity.(2) The relative proportions of stem and roots biomass increased gradually at the small-and medium-tree classes, and decreased gradually at the big-tree class. The proportion of branch and leaf biomass was just opposite. But no significant difference was found among different tree-size classes. The branch and leaf biomass located mainly in middle and bottom layers of tree crown at each tree size category. The aboveground biomass significantly linearly correlated with belowground biomass (P<0.001). The slope of the fitted linear model was0.31. Both dbh and tree height showed a significant exponential correlation with aboveground competition intensity (P<0.001). Competition intensity showed no significant relationships with crown ratio, stem to foliage biomass ratio and root to shoot ratio (P>0.05). But the ratio of tree height to dbh exhibited a significant power relationship with competition intensity (P<0.05). According to the explainable variability and the significance of coefficients in allometric models, it can be concluded that dbh is a reliable variable for estimating the above-and belowground biomass of Tilia amurensis. Thus, the growth stage and tree size should be involved in allometry for precise estimation of above-and belowground component biomass.(3) Crown structure of Tilia amurensis showed a certain plasticity response with different competition intensity. With the weakening of the competition intensity, the average levels of collateral branch length and branch diameter increased gradually; total branch numbers and branch angles of the first-order branch increased at early stage but decreased latter; there was no significant difference in the branch angle of the second-order branch (P>0.05); total branch numbers of the second-and third-order branch increased gradually (P<0.05); branch angle and current-year branch length of the third-order branch had no difference among classes, but they tend to decrease gradually. The longest first-order branch located in the bottom of the crown, when the diameter reached10cm, the longest branch grew at4-8m position from the treetop. Each levels of collateral branch length and branch diameter in each diameter class showed significant difference in every canopy levels (P<0.05), however, branch angles within each canopy levels were not significantly different (P>0.05). There were no difference in branch number proportion of the second-order branch between the upper and middle layer of the canopy (P>0.05), while they both had difference with the lower layer of the canopy (P<0.05). Third-order branch of middle layer of the canopy had the highest branch number proportion, and had significant difference with other layers (P<0.05). With the decrease of the competition intensity, the difference of current-year branch length in each canopy layers decreased. |
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