Abstract: [Objective] Understanding the relationship between above- and below-ground biomass is of profound significance to predict the biomass of forest ecosystem and global climate changes. This paper was aimed to test whether the aboveground biomass scaled isometrically with under-ground biomass of shrub layer plants and how forest management measures influenced such scaling relationships. [Method] Above-(y)and under-ground biomass(x)of shrub layer plants in natural evergreen broad-leaved forest and Chinese fir plantation in Fujian province (Nanping and Sanming) were harvested to test the biomass allocation patterns, a. Software SMATR (standardized major axis tests and routines)was used to calculate and analyze the allometric scaling a and exponent constant b, as the equation: log y=b+a log x. [Result] The scaling exponents for the shrub layer plants of young, middle-age, pre-mature and mature natural evergreen broad-leaved forests were 0.942, 1.003, 0.946, and 0.951, respectively. Furthermore, the scaling exponents were not differ significantly among the four stand ages of natural evergreen broad-leaved forests, indicating that above-ground biomass scaled isometrically with under-ground biomass. For the shrub layer plants of young, middle-age, pre-mature and mature Chinese fir plantations, the scaling exponents were 0.837, 0.817, 1.011, and 0.984, respectively. The 95% confidence intervals of such scaling exponents all covered the predicted theoretical value 1.0, showing that above-ground biomass scaled isometrically with below-ground biomass. [Conclusion] The above-ground biomass of understory scales nearly one to one with under-ground biomass in different regions and different types of forests. Although different forest tending measures appeared to affect the scaling constants, but not the scaling exponents of above-vs . under-ground biomass of shrub layer plants. Generally, the above- and under-ground biomass allocation patterns of shrub layer plants in natural evergreen broad-leaved forest and Chinese fir plantation in Fujian province were in consistence with the isometric biomass allocation theory. The research validated and developed the theory of isometric scaling of above- and under-ground biomass of forest vegetation.

Key words: shrub layer vegetation, biomass allocation, age groups, natural evergreen broad-leaved forest, Chinese fir plantation