Effects of tree size and competition on biomass allocation of five major afforestation tree species in Qingdao, Shandong Province of eastern China

Objective This paper explores the comprehensive effects of tree development stage and competition on biomass allocation of trees, so as to provide a theoretical basis for the optimization of functions of plantation ecosystem in the Laoshan area of eastern China.

Method Taking five main afforestation tree species in the Laoshan area of Qingdao, i.e. Pinus thunbergii, Pinus densiflora, Populus przewalskii, Robinia pseudoacacia, and Quercus acutissima as the research objects, we divided the sample trees in plot into diameter classes at 5 cm intervals, quantify the competition intensity of sample trees using Hegyi’s single tree competition index, and divide them into five competition levels. By harvesting and measuring the biomass of various tree organs, this study investigated the characteristics of biomass allocation and distribution among different tree species, as well as their responses to tree size and competition.

Result Leaf biomass was concentrated in the upper and middle layers of tree crown, while the proportion of branch biomass was the highest in the middle and lower layers. The proportion of trunk biomass was the largest (44.1%−69.9%), while the proportion of leaf biomass was the smallest (0.8%−13.1%); Except for Pinus densiflora, the underground biomass of other tree species increased with the increase of aboveground biomass, and the regression slope was Robinia pseudoacacia > Pinus thunbergii > Quercus acutissima > Populus przewalskii. Under competitive pressure, the investment in trunk and leaves of Robinia pseudoacacia increased significantly, while Pinus thunbergii preferentially increased the investment in roots. The interaction among tree species, diameter class, and competition intensity significantly affected the allocation patterns of various tree organs.

Conclusion The biomass allocation strategies of each organ during tree growth vary according to the physiological characteristics of tree species, and the strategies of fast-growing tree species in the competitive response are also different from those of other tree species. Tree biomass allocation is affected by synergistic effect of tree species characteristics, developmental stages and environmental pressures. This study provides basic data and scientific basis for further exploring the regulatory mechanisms of biotic and abiotic factors on the biomass allocation of trees and the functional optimization of plantation ecosystems.