Abstract:

Temperate forests in northeastern China play a key role in the national and global carbon budgets. However, relatively few studies were conducted in biomass allometry of these species, although understory tree species (including tree-like plants and typical shrubs) accumulate a substantial amount of nutrients and carbon. In this study, allometric equations for the organ (leaf, branch and root) and total biomass of 16 understory tree species were developed, and allometry of the organ biomass against plant size was analyzed. The result showed that 1) the forms and variables of optimal biomass equation varied with species and organs. The optimal equations for tree-like plants were power functions with diameter at 10 cm height (D₁₀) as the predictor. For typical shrubs, most of these equations were also power functions using crown area (CA) or crown area multiplying height (CAH) as predictors while the left few species fitted the other functions such as linear and quadratic polynomial equations. Generalized models regardless of species could be used to estimate biomass when the species-specific models were unavailable. 2) Models using plant height (H) or stem length (L) as independent variables in the biomass equations only improved the fit for most of the typical shrubs but not for the tree-like plants. Percentage increase in determination coefficients (R²) with adding L in the allometric equations was smaller than that with adding H. 3) The relationship between biomass of the understory with the plant size complied with allometric theory (P<0.05), but the power varied. For tree-like plants, power exponents of biomass components against D₁₀ varied from 1.712 to 2.555, and old branch biomass, branch biomass, large root biomass belowground biomass and total biomass nearly scaled as 8/3 power of D10. For typical shrubs, the ranges of power exponents scaling with CA and CAH were 0.688－1.293 and 0.527－1.017, respectively. In the contrast, foliage biomass, new branch biomass, large root biomass, belowground biomass and total biomass scaling with CA, and old branch biomass, branch biomass and aboveground biomass scaling CAH were both isometry.

Key words: understory tree species, biomass equations, allometry, temperate forest