Carbon sink turning points loom for subtropical needle-leaved forests after 2070

Researchers used the process-based LANDIS-II landscape model to simulate forest dynamics in China’s Guangdong-Hong Kong-Macao Greater Bay Area from 2020 to 2100, running four Shared Socioeconomic Pathways climate scenarios alongside a current climate baseline. Their central question was whether, and when, the carbon sink function of these forests might approach a turning point, defined as the statistical threshold at which aboveground biomass accumulation rates shift from positive to negative growth.

The results, published in Carbon Balance and Management, reveal sharply divergent trajectories for the two dominant forest types. Evergreen broad-leaved forests maintain positive aboveground biomass growth throughout the entire century in every scenario tested. Evergreen needle-leaved forests, by contrast, are projected to experience carbon sink turning points after 2070 across all scenarios, with the earliest onset appearing under the higher-emission SSP3-7.0 pathway. That split matters because it suggests the risk of reversal is not distributed evenly across the landscape but concentrated in a specific, and arguably more vulnerable, slice of the region’s forest estate.

To locate where those reversals would begin, the team applied a piecewise slope detection approach to their simulation outputs. The answer was reassuring in one respect: turning point zones remain spatially limited, covering less than 0.5 percent of the total forest area. But their placement is telling. The zones cluster in ecologically fragile areas of Zhaoqing, a prefecture within the Greater Bay Area where forest fragmentation and human disturbances overlap. Forests that are already broken into smaller patches and subject to ongoing human pressure, the modelling implies, are the first to cross the threshold at which biomass accumulation flips into decline.

Perhaps the most counterintuitive finding concerns the moderate-emission scenario. Under SSP2-4.5, the region achieves the highest total aboveground biomass accumulation of any pathway simulated, yet that same scenario also produces the most rapid post-peak biomass decline. In other words, the pathway that delivers the biggest carbon gains over the century also sets up the steepest fall once the peak has passed. The authors interpret this pattern as evidence that carbon sink turning points mark the breakdown of stable carbon budget equilibria, and they argue that such turning points can serve as early warning proxies for broader shifts in ecosystem functional status.

The methodological choice underpinning these conclusions is worth unpacking. Early-warning signal approaches used elsewhere in ecology are largely limited to retrospective historical analysis, which makes it difficult to say anything about the future. Running it from 2020 to 2100 under four SSP scenarios and a baseline allowed the researchers to compare how different climate futures reshape the timing and geography of carbon sink failure in a single, consistent framework.

The Shared Socioeconomic Pathways themselves provide the scenario architecture. Because the needle-leaved turning points appear after 2070 in every scenario, the study indicates that some degree of reversal risk is baked into the century regardless of emissions trajectory, but the timing of onset shifts with the climate pathway, arriving earliest under the most forcing-intensive scenario. The broad-leaved forests’ unbroken positive growth through 2100 suggests that species composition is a decisive variable in how long a subtropical landscape can keep sequestering carbon above ground.

Spatially, the concentration of turning point zones in Zhaoqing carries practical weight. The study characterises these areas as ecologically fragile, with overlapping forest fragmentation and human disturbances, conditions typical of landscapes squeezed between conservation priorities and urban or agricultural expansion. Because the zones occupy less than 0.5 percent of total forest area, the findings point to a targeted rather than region-wide management problem: a small, identifiable footprint where intervention could plausibly delay or prevent the crossing of critical growth reversal thresholds.

That targeted logic shapes the study’s management recommendations. The authors recommend prioritising adaptive forest management for needle-leaved forests, especially within the identified turning point zones, with the stated aim of improving ecosystem resilience and sustaining regional carbon sequestration capacity before critical growth reversal thresholds are reached. Because the outputs are derived from multi-scenario, spatially explicit process modelling, the team frames them as policy-relevant insights for managing coupled carbon-climate-human systems in urban-affected subtropical forests, a framing that speaks directly to planners in one of the most densely urbanising regions on Earth.

Several caveats deserve emphasis. These are model projections, not measurements of biomass change that has already occurred; the turning points lie in the future by construction, and their dates depend on the assumptions embedded in each SSP scenario and in the LANDIS-II parameterisation. The study also focuses on aboveground biomass, so belowground carbon pools and soil carbon are outside the reported turning point analysis. The article was published as open access on 9 October 2026 and is being shared early as a peer-reviewed, accepted version that remains citable and carries a permanent DOI, subject to further edits before the final Version of Record appears. Even with those qualifications, the core message stands: within the Greater Bay Area’s subtropical forests, the carbon sink story to 2100 is not one story but two, and the needle-leaved half carries a date after 2070 when its contribution may begin to run in reverse.

Subject of Research: Projected turning points in subtropical forest carbon sinks in southern China under multiple climate scenarios

Article Title: Turning points of subtropical forest carbon sinks in southern China: spatiotemporal dynamics and management insights

Article References: Shao, Z., Wu, Z., Li, Y., Zeng, H., Zheng, G., Liu, G., Gao, Y., & Gong, J. (2026). Turning points of subtropical forest carbon sinks in southern China: spatiotemporal dynamics and management insights. Carbon Balance and Management. https://doi.org/10.1186/s13021-026-00530-5

Image Credits: AI Generated

DOI: 10.1186/s13021-026-00530-5

Keywords: forest carbon sink, subtropical forests, Greater Bay Area, LANDIS-II, Shared Socioeconomic Pathways, aboveground biomass, evergreen needle-leaved forest, evergreen broad-leaved forest, climate scenarios, turning point zones, adaptive forest management, Zhaoqing