Research Background
Forest carbon sequestration is an important pathway for mitigating global climate change. The temperate forests in Northeast China cover a vast area and store substantial carbon, playing a crucial role in the nation’s carbon balance and regional climate regulation. Therefore, accurately assessing their carbon sink capacity is of great significance. However, estimating forest carbon sinks does not simply yield a single numerical value. Observation methods, sampling timing, spatial heterogeneity, and measurement errors in component analysis can all affect the reliability of the results. Current research lacks a systematic analysis of the sources and contributions of uncertainty, which hinders comparisons among different studies and constrains further improvements in the accuracy of forest carbon sink estimations.
Based on this, the research team led by Professor Zhu Jiaojun from the Shenyang Institute of Applied Ecology, Chinese Academy of Sciences, took typical secondary forest ecosystems in Northeast China as their study object. Combining plot surveys, soil respiration measurements, and long-term monitoring of soil carbon stocks, they systematically evaluated the carbon sink strength of different forest stands and identified the sources of uncertainty. Furthermore, they proposed a framework for estimating carbon sinks with lower uncertainty, providing an important reference for improving the accuracy of forest carbon sink accounting. The study was published in the Journal of Forestry Research.
Key Findings
(1) The annual average NPP of the three forest types was 6.90 ± 1.48, 7.36 ± 1.75, and 6.54 ± 1.40 t ha⁻¹ a⁻¹, respectively, with no significant overall difference. Carbon input was primarily concentrated in the aboveground biomass.
(2)The annual average total Rs values for the three forest types were 7.21 ± 1.04,8.66 ± 0.58, and 5.24 ± 0.33 t ha⁻¹ a⁻¹, respectively; the Rh values were 4.91 ± 0.98,5.49 ± 1.09, and 3.86 ± 0.21 t ha⁻¹ a⁻¹, respectively. The Mongolian oak forest exhibited the highest Rs and Rh values; however, its relatively high net primary productivity (NPP) was offset by strong soil carbon sequestration, ultimately resulting in the lowest net ecosystem productivity (NEP). This indicates that when assessing forest carbon sequestration capacity, one should not rely solely on plant productivity—soil carbon flux is equally critical.
(3) The NEP values for secondary mixed broadleaf forests, Mongolian oak forests, and larch plantations were 1.99 ± 1.78, 1.87 ± 2.06, and 2.68 ± 1.42 t ha⁻¹ year⁻¹, respectively, indicating that all three forest types generally function as carbon sinks. Among them, the larch plantation had the highest NEP value, while the Mongolian oak forest had the lowest.
Figure 1. Comparison of Rs, Rh, and NEP among the three forest stands;
Table 1. Net Primary Productivity (NPP, t ha⁻¹ a⁻¹) and its uncertainty for the three forest stands
(4) Although all three forest types act as carbon sinks, traditional NEP estimates exhibit considerable uncertainty.
(5) The uncertainty decomposition results show that fine roots contribute the most to the uncertainty in NPP and NEP; followed by Rs. Leaves also have a certain impact, while shrubs, herbs, and coarse roots contribute relatively little.
(6) The "Low Uncertainty Carbon Sink" framework significantly reduces the uncertainty associated with carbon sink estimation and enhances the reliability of the results by focusing on the tree trunk, coarse root, and soil carbon pools.
Table 2. Relative contribution of ecosystem components to NEP uncertainty
Research Methodology
The study was conducted at the Qingyuan Forest Ecosystem National Field Scientific Observation and Research Station of the Chinese Academy of Sciences. Three typical forest stands—secondary mixed broadleaf forest, Mongolian oak forest, and larch plantation—were selected, and permanent sample plots were established around flux towers. The experiment primarily collected data on various components, including NPP, Rs, Rh, as well as soil temperature and moisture levels.
Soil respiration was measured in situ using the PS-9000 Portable Soil CO₂ Flux System (Beijing Lijia United Technology Ltd.). Researchers pre-buried PVC rings within the sample plots; during measurement, the soil respiration chamber was hermetically sealed to these rings, and soil flux was calculated based on changes in gas concentrations within the chamber. At the same time, root-cutting treatments were implemented to distinguish between total Rs and Rh, which is primarily generated by microbial decomposition. Formal observations were conducted under stable weather conditions at intervals of 7–10 days.
In terms of data processing, the study uses soil temperature and moisture content to model soil respiration and extends this approach to continuous flux estimation. It calculates annual-scale Rs and Rh, thereby estimating carbon sinks and analyzing sources of uncertainty. Building on this foundation, the study further introduces the concept of “low-uncertainty carbon sinks,” which includes only stable carbon pools that make significant long-term contributions to carbon sequestration and exhibit relatively low measurement errors—namely, stem NPP plus coarse root NPP plus changes in soil carbon—to enhance the reliability of forest carbon sink estimates.
Revelation
Forest carbon sink assessments should not only focus on the amount of carbon sequestered but also address whether the carbon can be stored long-term and whether the results are reliable. In the future, by strengthening long-term monitoring of stable carbon pools and underground processes and refining the uncertainty analysis framework, we can enhance the accuracy of forest carbon sink accounting and provide more reliable support for ecological carbon sink management and carbon neutrality goals.
Journal: Journal of Forestry Research [Impact Factor: 4.1]
Research institutions: Institute of Applied Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, and others.
Study site: Qingyuan Forest Ecosystem National Field Scientific Observation and Research Station, Chinese Academy of Sciences
Equipment used: PS-9000 Portable Soil CO₂ Flux System
DOI: https://doi.org/10.1007/s11676-026-01998-0