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Open access Sep 2026

Region-specific forest structure pathways reveal climate effects on old-growth tropical forest biomass

Old-growth tropical forests store vast amounts of carbon in their aboveground biomass (AGB), yet the relative roles of abiotic factors such as climate, soil, and topography in governing its spatial distribution remain poorly understood. In particular, the degree to which climate acts on AGB through forest structure is still poorly quantified at the pantropical scale. Using a pantropical dataset of more than 2,000 old-growth forest plots and a structure-explicit framework, we assess how climate influences AGB through its effects on four structural attributes: basal area, mean diameter, stem density, and basal area-weighted wood density. We find that climate shapes AGB primarily through its effects on forest structure. However, structural attributes respond to climate in opposite directions, so climate’s net effect on AGB largely cancels out, and no clear climate-AGB relationship emerges across tropical regions. Moreover, only wood density responds consistently, decreasing with annual precipitation and increasing with precipitation seasonality, whereas all other attributes respond to climate differently from one region to another. This geographical variation further obscures any global climatic signal on AGB and points to the role of biogeographic history in shaping forest structure. Our findings highlight the central role of the climate-structure nexus in explaining AGB variation, and call for structure-explicit models to improve carbon stock predictions and inform climate adaptation strategies.

Pauline Depoortere, D. Bauman, A. Fayolle et al. · 0 citations
Review Open access Jul 2026

Climate Change Impacts on Alpine Vegetation: The Role of Microclimatic Variability

Global surface temperatures have increased by about 1.1°C relative to 1850–1900, with 2011–2020 being the warmest decade on record and accompanied by changing precipitation patterns. Warming is amplified in alpine regions such as the European Alps, where temperature increases have been roughly twice the northern hemispheric average since the late 19th century, alongside contrasting precipitation trends between northern (wetter) and south-eastern (drier) areas. Alpine ecosystems, defined as treeless zones above the tree line, are highly sensitive to climate change, exhibiting upward species shifts, phenological changes, vegetation restructuring, and local extinctions. However, strong microclimatic heterogeneity may buffer these impacts. This study presents a narrative literature review of microclimatic buffering in alpine vegetation. The evidence was synthesized showing how topography-driven radiation differences, wind-induced cold-air pooling, and snow dynamics generate fine-scale habitat variability. These processes create microhabitats that can reduce exposure to macroclimatic warming and support potential microrefugia for plant species. The study argues that microclimatic buffering is a key but still insufficiently understood mechanism shaping alpine vegetation responses to climate change. Improved understanding of its limits is essential for more accurate predictions of vegetation dynamics and for informing conservation strategies in mountain ecosystems.

Samyog Dhakal · 0 citations
Open access Aug 2026

Spatiotemporal Dynamics and Environmental Associations of Vegetation Carbon Sinks in the Middle and Lower Yellow River Basin, China

Vegetation carbon sinks are an important component of the terrestrial carbon cycle, and net ecosystem productivity (NEP) is widely used to indicate ecosystem carbon-sink strength. However, the long-term dynamics and environmental associations of vegetation carbon sinks in the middle and lower Yellow River Basin remain insufficiently understood. Based on remote-sensing net primary productivity (NPP) and an empirical heterotrophic-respiration model, annual NEP was estimated for 2001–2024. Theil–Sen trend analysis, the Mann–Kendall test, coefficient of variation, optimal-parameter geographical detector (OPGD), and regression residual analysis were applied. Basin-mean annual NEP increased from approximately 214 to 425 g C m−2 yr−1, with significantly increasing areas accounting for 89.93% of the study area. Areas with NEP above 300 g C m−2 yr−1 expanded from 18.51% to 78.86%. Precipitation and solar radiation showed the highest explanatory power for NEP spatial differentiation, with mean q values of 0.538 and 0.490, and their interaction reached 0.722. Comparison with a published NEP product, parameter-sensitivity analysis, and an NPP-based robustness test supported the main temporal patterns and factor rankings. The residual-derived non-climatic component exceeded 40% of the combined component-trend magnitude across approximately 94% of the study area, but should not be interpreted as a direct measure of human activities. These findings support regional carbon-sink monitoring, water-constrained ecological restoration, and land-use management.

Chenyang Li, Lianhai Cao, Haodong Ji et al. · 0 citations
Open access Aug 2026

Soil Moisture Thresholds for the Temperature Sensitivity of Ecosystem Respiration

Ecosystem respiration (ER) is the largest source of biogenic CO2 to the atmosphere, and its temperature sensitivity (Q10) before reaching maximum values is crucial for understanding land–climate feedback. However, despite decades of studies showing that Q10 varies considerably across space, time, and biomes, the mechanisms underlying this variability remain unresolved. Here we demonstrate that global variation in Q10 can be reconciled within a unified hydrothermal framework. Using data from 142 eddy covariance sites around the world, we show that Q10 exhibits unimodal responses to soil moisture. At each site, Q10 first increases with soil moisture, peaks at a threshold (SMth), and then declines. This SMth is ecosystem‐specific, which consistent with mechanisms involving plant–soil–microbial interactions, shaped by long‐term hydroclimatic regimes and soil physical constraints. Global mapping of SMth shows that about 25% of the planet's vegetated land currently operates above SMth, including many carbon‐rich peatlands and tropical forests, where moderate drying may amplify temperature sensitivity and accelerate carbon loss. By identifying soil moisture thresholds as a first‐order control on Q10, our study provides a unifying mechanism that links hydrological state to the thermal sensitivity of carbon fluxes. This framework offers a predictive basis for anticipating respiration responses to climate change by explicitly resolving whether shifts in soil moisture move ecosystems toward or away from these critical thresholds.

Qin Zhang, Song Wang, Qin-Yu Zheng et al. · 0 citations
Open access Jul 2026

Temporal dynamics of carbon fluxes in a tropical montane forest ecosystem in Southern Ecuador

Tropical rainforests represent major carbon reservoirs and play a critical role in regulating carbon dynamics and climate. Quantifying their carbon fluxes is essential for understanding ecosystem responses to climate variability and improving future climate change projections. In this study, we investigated interannual and seasonal variability in gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem productivity (NEP) in a montane tropical rainforest in Southern Ecuador using eddy-covariance measurements from 2019 to 2024. GPP showed rather low interannual variability with a gradual increase from approximately 7.79–8.92 gCm − 2 day − 1 over the study period. Seasonal differences were generally weak, although a more pronounced contrast was observed in 2024 with higher GPP during the wet phase (10.26 gCm − 2 day − 1 ) and compared to the dry phase (7.38 gCm − 2 day − 1 ). The ecosystem consistently functioned as a net carbon sink, with maximum carbon uptake occurring in 2024 (NEP approximately −3.97 gCm − 2 day − 1 ). Despite the general stability of GPP, variability in net carbon exchange was primarily driven by changes in Reco, indicating a stronger sensitivity of respiration to environmental fluctuations. Principal component analysis (PCA) revealed that carbon flux variability reflects a combination of radiation and moisture controls. Incoming solar radiation (Rg) showed the strongest association with GPP, whereas soil temperature (Ts) and soil moisture (SM) appeared to influence variations in Reco. Furthermore, we assessed the influence of ENSO phases on carbon fluxes and found reduced productivity during El Niño conditions, associated with elevated Ts and slight reduced SM and Rg. These results highlight the sensitivity of tropical montane forests to both local environmental drivers and large-scale climate variability. Overall, our findings demonstrate that while short-term photosynthetic processes remain generally stable, respiration processes were identified as important correlates of interannual variability in carbon balance, highlighting their relevance to tropical carbon dynamics.

Charuta Murkute, F. Pucha-Cofrep, Galo Carrillo-Rojas et al. · 0 citations
Review Open access Aug 2026

The Role, Issues, and Challenges of Afforestation in Climate Change Mitigation

Afforestation can contribute to climate-change mitigation when tree establishment is matched to ecological context and sustained by long-term management, but its net climatic effect is not uniformly cooling. Existing syntheses often emphasize carbon sequestration while treating biophysical, hydrological, disturbance, and socioeconomic evidence separately. Here, we provide a structured integrative review. We distinguish afforestation from reforestation, natural regeneration, forest restoration, and improved management. We explicitly assess evidence from global modeling, remote sensing, meta-analyses, long-term observations, and regional case studies. Global forests cover about 4.14 billion ha in 2025, while annual net forest loss remained about 4.12 million ha yr−1 during 2015–2025. Global forests were a sink of about 3.5 ± 0.4 Pg C yr−1 in the 2010s, but this existing-forest sink should not be interpreted as an afforestation-specific removal rate. Humid tropical and subtropical regions generally have the greatest potential for net climatic cooling. In contrast, afforestation at snow-covered high latitudes may cause substantial albedo-driven warming, while water-limited regions require careful species selection and conservative planting densities. Soil carbon gains are most consistent on former croplands and other low-carbon degraded lands, but responses on carbon-rich grasslands are highly variable. Long-term benefits further depend on disturbance resilience, permanence, land competition, financing, and credible monitoring. Additionally, we identify five priorities for the future: climate-smart adaptive silviculture, digital forestry with field-calibrated uncertainty, permanence and disturbance-risk accounting, sustainable forest bioeconomy, and integrated international governance and finance.

Quimei Wang, Qiang Zhu, Wei Liu et al. · 0 citations

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