Abstract
The Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) was first introduced to the southeastern Horqin sandy land in the mid-1950s. Since then, it has been widely planted and has become the most important conifer species in Northern China, providing significant ecological, economic and social benefits. However, its function in sequestering carbon at different developmental stages has been little studied. In this study, twenty plots inventory and destructive sampling of eight trees were conducted in 12-, 19-, 34-, 48- and 58-year-old Mongolian pine stands of China. Allometric biomass equations (ABEs) for tree components were established and used to determine the magnitude and distribution of tree biomass and carbon density. The carbon density of the understory, forest floor and soil was also determined. The ABEs with age as the second variable could simply and accurately determine the biomass of plantation tree branches, foliage and fruit, which were considerably influenced by age. With increasing stand age, the proportion of stem biomass to total tree biomass increased from 22.2% in the 12-year-old stand to 54.2% in the 58-year-old stand, and the proportion of understory biomass to total ecosystem biomass decreased, with values of 7.5%, 4.6%, 4.4%, 4.1% and 3.0% in the five stands. The biomass of the forest floor was 0.00, 1.12, 2.04, 6.69 and 3.65 Mg ha−1 in the five stands. The ecosystem carbon density was 40.2, 73.4, 92.9, 89.9 and 87.3 Mg ha−1 in the 12-, 19-, 34-, 48-, and 58-year-old stands, in which soil carbon density accounted for the largest proportion, with values of 67.4%, 76.8%, 73.2%, 63.4%, and 57.7% respectively. The Mongolian pine had the potential for carbon sequestration during its development, especially in the early stages, however, in the later growth stage, the ecosystem carbon density decreased slightly.
Highlights
Under the influence of anthropogenic activities and climate change, the concentration of greenhouse gases such as carbon dioxide (CO2 ), methane, and nitrogen oxides in the atmosphere has increased and brought about a series of environmental problems
R2 values increased slightly after considering the age effect in Allometric biomass equations (ABEs), for the sake of simplicity and accuracy, equations with D as a single variable were recommended for biomass determination of the above components and were used in the subsequent analysis
For the biomass of branch, foliage and fruit, the results of ABEs with a single variable were poor, with R2 values of 0.91, 0.83, and 0.59, respectively; the R2 values increased to 0.95, 0.91, and 0.92 after considering the age effect, indicating that the biomass of these components was significantly affected by age
Summary
Under the influence of anthropogenic activities and climate change, the concentration of greenhouse gases such as carbon dioxide (CO2 ), methane, and nitrogen oxides in the atmosphere has increased and brought about a series of environmental problems. The global atmospheric CO2 concentration reached 391 ppm in 2011, 40% higher than the preindustrial level [1]. As the largest carbon reservoir in terrestrial ecosystems, play an important role in mitigating elevated atmospheric CO2 concentrations and preventing global warming [2,3]. Forests 2019, 10, 197 type of forest, planted forests have the dual mission of timber production and ecological restoration, accounting for 7% of global forest area and having an important impact on the global carbon cycle [4]. Since the late 1970s, China’s government has launched a series of national forestry projects, such as the Three North Shelterbelt
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