Nature-based Solutions can help restore degraded grasslands and increase carbon sequestration in the Tibetan Plateau

The study addresses how Nature-based Solutions (NbS) can restore degraded grasslands and enhance carbon sequestration on the Tibetan Plateau to support carbon neutrality targets. Against the backdrop of national and global net-zero commitments, the Tibetan Plateau represents a large potential terrestrial carbon sink across extensive grassland ecosystems. However, grassland degradation from overgrazing, climate change, and land use change has reduced soil organic carbon and turned some areas from sinks to sources. Prior restoration initiatives evolved from site rehabilitation to broader goals (biodiversity, soil quality, carbon), yet substantial gaps remain in coordinated approaches, evaluation methods, and stakeholder alignment. The authors posit that NbS, integrating local Tibetan traditional knowledge with science, can provide an effective, scalable pathway to protect intact systems, manage working lands, and restore degraded areas to increase carbon storage. The research aims to synthesize evidence, propose a conceptual NbS framework tailored to Tibetan grasslands, and quantify potential carbon sink gains under future scenarios.

The paper synthesizes prior work on terrestrial carbon sinks in China and the Tibetan Plateau, highlighting estimates of regional carbon sinks, vegetation and soil carbon stocks, and permafrost carbon. It reviews global and national literature on NbS and natural climate solutions, including pathways such as reforestation, grazing management, and ecosystem restoration, and case studies demonstrating NbS benefits (e.g., invasive tree removal improving streamflow resilience, frameworks linking social-ecological interactions to adaptation). It notes that NbS could significantly reduce China’s emissions and that applications in Tibetan grasslands remain limited. The review covers restoration outcomes (e.g., grazing exclusion, artificial grassland) and their contributions to biomass and soil carbon, but also documents uncertainties in remote-sensing-based degradation assessments, inconsistent criteria, and divergent stakeholder perspectives. It emphasizes integrating indigenous knowledge, inclusive governance, and adaptive management as identified in international NbS standards.

The study combines a literature review and meta-analysis with ecosystem modeling to assess NbS potential for Tibetan grasslands. Meta-analysis: Using Google Scholar and CNKI, the authors screened studies on grazing regimes, grazing exclusion, and artificial grasslands in the Tibetan Plateau that reported aboveground biomass (AGB), belowground biomass (BGB), soil organic carbon (SOC), plant litter, and microbial biomass carbon (MBC), without confounding interventions. Data from 284 publications were synthesized using response ratios with inverse-variance weighting and bootstrap 95% confidence intervals to quantify treatment effects. Degradation classification: Grassland degradation was mapped using NDVI trends (GIMMS AVHRR 3rd generation, growing seasons 1982–2020) in Google Earth Engine. Sen’s slope and Mann–Kendall tests identified significant trends to classify degradation stages. Carbon sequestration baseline and potential: Net ecosystem productivity (NEP) from the BEPS model (1981–2019) was used to define maximum historical carbon sequestration (Cmax) for each grassland. Future trajectories: The ORCHIDEE-MICT land surface model, driven by ISIMIP3b bias-corrected climate projections from five ESMs (GFDL-ESM4, IPSL-CM6A-LR, UKESM1-0-LL, MPI-ESM1-2-HR, MRI-ESM2-0) and varying atmospheric CO2, simulated carbon sequestration from 1960 to 2100 under SSP1-2.6, SSP3-7.0, and SSP5-8.5. NbS scenario design: Starting in 2020, NbS interventions corresponding to protect, manage, and restore pathways were assumed to be progressively implemented across degraded grasslands, achieving optimal state (Cmax) by 2060 and maintained thereafter. The additional NbS sequestration was calculated as ΔCNbS = Cmax − C2060, aggregated across pathways and phased in linearly from 2021 to 2060, then sustained to 2100. Framework development: A conceptual NbS framework adapted from IUCN Global Standard criteria was constructed, structured around four stages—theory, identification, practice, goal—and applied to classify 19 restoration techniques into protect, manage, and restore pathways and to design a project evaluation roadmap.

- Scale of degradation and carbon loss: About 40% of Tibetan grasslands are degraded (heavy 8–5.6%, moderate ~10–4.4%, light ~18–23.7% across estimates). Degradation has resulted in a loss of approximately 1.01 Pg soil carbon since the 1980s, double the potential accumulation from climate change and elevated CO2. - Restoration outcomes: Restored grasslands show on average 0.14 kg C/m2 (29.2%) higher plant biomass carbon and 1.15 kg C/m2 (12.3%) higher SOC density than degraded grasslands. Grazing exclusion significantly increases litter, AGB, and BGB relative to grazing, while heavy grazing reduces SOC and AGB; root biomass is generally unaffected by grazing intensity. Artificial grasslands sequester carbon via plant growth and soil transfer. Estimated carbon sink potentials: grazing exclusion ~49.87 Tg C/yr; artificial grassland ~34.33 Tg C/yr. - NbS framework and techniques: A four-stage NbS framework (theory, identification, practice, goal) centered on local herders’ traditional knowledge was defined. Nineteen restoration techniques were classified into protect, manage, and restore pathways. - Modeled carbon sequestration trajectories: Without NbS, projected 2060 carbon sink is 41 Tg C/yr (SSP1-2.6), 62 Tg C/yr (SSP3-7.0), and 70 Tg C/yr (SSP5-8.5). With NbS, additional sink by 2060 is +21 Tg C/yr (SSP1-2.6), +18 Tg C/yr (SSP3-7.0), and +15 Tg C/yr (SSP5-8.5), corresponding to total NbS contributions of 15–21 Tg C/yr depending on scenario. - Breakdown of NbS contributions: Protect lightly degraded grasslands (e.g., optimized grazing) ~10.5 Tg C/yr; manage moderately degraded (e.g., grazing exclusion) ~2.5 Tg C/yr; restore heavily degraded (e.g., artificial grassland) ~5.0 Tg C/yr.

Findings demonstrate that Nature-based Solutions can substantially enhance the Tibetan Plateau grassland carbon sink beyond climate-driven trends, directly addressing the need for scalable, coherent restoration strategies to support carbon neutrality. The meta-analysis confirms that reducing grazing pressure and implementing targeted restoration improve biomass and SOC, thereby increasing sequestration. Modeling shows that NbS provide significant additional sinks across diverse socioeconomic trajectories, with the largest gains from protecting lightly degraded lands through improved management. The NbS framework aligns ecological goals with socio-cultural contexts by placing local herders at the center of decision-making, improving legitimacy and long-term viability. It offers a systematic classification of techniques and a monitoring and evaluation roadmap to adaptively manage projects, balance trade-offs, and mainstream sustainability. Addressing uncertainties in degradation assessments and integrating stakeholders mitigates conflicts and enhances project outcomes, reinforcing the role of NbS as a complement to, not a substitute for, decarbonization.

The paper provides an integrated evidence base and a practical, culturally grounded NbS framework to restore degraded Tibetan grasslands and increase carbon sequestration. It quantifies added carbon sink potentials of 15–21 Tg C/yr by 2060, with protection and improved management delivering the largest gains. Contributions include: a four-stage NbS conceptual framework tailored to the Tibetan Plateau; classification of 19 restoration techniques into protect, manage, and restore pathways; and coupled meta-analysis–modeling quantification of NbS benefits under multiple SSPs. Future work should validate and scale NbS projects, integrate long-term monitoring, refine degradation mapping and evaluation methods, coordinate with regional ecological zoning, optimize project timing and scale, and further embed indigenous knowledge and biodiversity conservation. NbS should be deployed alongside aggressive emissions reductions and ecosystem connectivity protection.

- Degradation assessment uncertainty due to varied remote sensing datasets, inconsistent criteria, limited sample sizes, and difficulty capturing soil moisture, nutrients, and plant composition, leading to divergent estimates of degraded area and severity. - Lack of long-term, large-scale experimental evidence hampers causal attribution of drivers and restoration effectiveness. - Overlapping, top-down projects with multiple stakeholders complicate evaluation and may face local opposition if herders’ interests are not integrated. - Modeling assumptions include linear NbS implementation to 2060, restoration to and maintenance at optimal states, and reliance on a single land surface model (ORCHIDEE-MICT) and selected climate forcings, which introduce structural and scenario uncertainties. - Transferability and socio-economic feasibility depend on governance, funding, land tenure security, and sustained community engagement.