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Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests
Abstract
The world's forests influence climate through physical, chemical, and biological processes that affect planetary energetics,
the hydrologic cycle, and atmospheric composition. These complex and nonlinear forest-atmosphere interactions can dampen or
amplify anthropogenic climate change. Tropical, temperate, and boreal reforestation and afforestation attenuate global warming
through carbon sequestration. Biogeophysical feedbacks can enhance or diminish this negative climate forcing. Tropical forests
mitigate warming through evaporative cooling, but the low albedo of boreal forests is a positive climate forcing. The evaporative
effect of temperate forests is unclear. The net climate forcing from these and other processes is not known. Forests are under
tremendous pressure from global change. Interdisciplinary science that integrates knowledge of the many interacting climate
services of forests with the impacts of global change is necessary to identify and understand as yet unexplored feedbacks
in the Earth system and the potential of forests to mitigate climate change.
... Forests are fundamental to maintaining ecological stability and advancing sustainable development [1]. Comprising one-third of Europe's landmass, forest ecosystems present significant potential for climate change mitigation efforts by policymakers and land managers [2]. ...
... Forest cover dynamics strongly modulate land surface temperature (LST) through coupled biophysical and biogeochemical mechanisms [3][4][5][6]. From a biogeochemical perspective, forests induce planetary-scale cooling primarily via photosynthetic carbon sequestration, which lowers atmospheric CO 2 concentrations [1,[7][8][9]. Concurrently, biophysical regulation occurs through three countervailing processes: (1) enhanced evapotranspiration promotes localized cooling by converting sensible to latent heat flux [10,11]; (2) reduced surface albedo increases solar radiation absorption [12][13][14], potentially inducing localized warming [1]; and (3) thermal isolation by vegetation affects surface-atmosphere heat transfer processes, thereby lowering the LST [15][16][17][18]. Collectively, these antagonistic mechanisms demonstrate that forests modulate LST through multifaceted modifications to surface energy balance and thermodynamic properties [5,18,19]. ...
... From a biogeochemical perspective, forests induce planetary-scale cooling primarily via photosynthetic carbon sequestration, which lowers atmospheric CO 2 concentrations [1,[7][8][9]. Concurrently, biophysical regulation occurs through three countervailing processes: (1) enhanced evapotranspiration promotes localized cooling by converting sensible to latent heat flux [10,11]; (2) reduced surface albedo increases solar radiation absorption [12][13][14], potentially inducing localized warming [1]; and (3) thermal isolation by vegetation affects surface-atmosphere heat transfer processes, thereby lowering the LST [15][16][17][18]. Collectively, these antagonistic mechanisms demonstrate that forests modulate LST through multifaceted modifications to surface energy balance and thermodynamic properties [5,18,19]. ...
Forest ecosystems critically regulate land surface temperature (LST) from local to regional scales. Over the last three decades (1986–2016), increasingly frequent and severe disturbances have substantially altered the European forest canopy structure and carbon storage. However, the biophysical interactions between forest disturbance severity (FDS) and LST, particularly their spatiotemporal dynamics, remain insufficiently quantified at regional-to-continental scales. This study integrated multi-source, high-resolution remote sensing data spanning 1986–2016 to systematically investigate European FDS and its biophysical control over LST. We find significant spatiotemporal heterogeneity in FDS, which decreased markedly from 5.92 ± 4.6 in 1986 to 0.35 ± 2.36 in 2016, stabilizing after a sharp decline pre-2000. Concurrently, the mean regional LST exhibited significant warming trends, increasing from −27.04 ± 10.15 K to 16.47 ± 10.67 K, and declining FDS indirectly contributed up to 65% of this temperature rise. Mechanistically, the reduced FDS enhanced the secondary forest leaf area index (LAI), decreasing surface albedo and increasing net radiation absorption, thereby inducing positive radiative feedback that drives surface warming. Our findings demonstrate that the carbon sequestration benefits accrued during forest recovery can be partially offset by associated biophysical warming effects. This evidence is crucial for optimizing European forest management strategies to balance carbon sink enhancement and climate regulation functions.
... Terrestrial surface energy balance refers to the equilibrium between incoming solar radiation, energy stored in soil and plant biomass, and outgoing energy in the form of energy reflected (albedo) and energy used for heat and evapotranspiration, typically measured as surface temperature (Schulze et al., 2019;Still et al., 2019). Along with mass balance, understanding this energy balance is essential for managing ecosystems, predicting their responses to climate change and assessing their role in carbon and water cycles (Bonan, 2008). Emerging remote sensing methods can capture states and processes related to mass and energy exchange (Hall et al., 1992), but applying these methods to prairie restoration options remains largely underexplored (Blackburn et al., 2021). ...
... Similar effects of productivity and energy balance have been noted for forests (e.g. Bonan, 2008) but have generally not been considered for grasslands, which cover roughly 40 percent of terrestrial surfaces and dominate the interannual variability in the terrestrial carbon sink (Poulter et al., 2014;Ahlström et al., 2015;Wang et al., 2022), offering significant climate mitigation potential. In our study, these effects were detectable in the altered productivity, albedo and surface temperature in treatment plots (Figs 2, 5, 6). ...
... For example, the carbon benefits of woody plants may come with accruing costs of biodiversity loss in the original grassland ecosystem, threatening the ecosystem services provided by grasslands (Veldman et al., 2015;Pellegrini et al., 2016). Although clearing forests releases carbon stored in trees, it alters the albedo and evapotranspiration patterns, leaving the overall net climate cooling or warming unsettled (Bonan, 2008;Luyssaert et al., 2018;Temperton et al., 2019). Thus, we recommend long-term strategic investigation into the impact of grassland restoration practices, considering not only diversity and productivity but also surface-atmosphere feedbacks in the context of various management treatments that include grazing and burning, which have been an integral part of historical prairie management. ...
Grassland restoration efforts aim to reestablish vegetation cover and maintain ecosystem services. However, there is a lack of systematic evaluation of the effects of grassland restoration and management strategies on biodiversity, productivity and surface–atmosphere feedbacks affecting climate.
Through a multiyear grassland restoration experiment in a tallgrass prairie site in Nebraska, USA, we investigated how different management practices affected biodiversity, productivity and surface–atmosphere feedbacks using a combination of in situ measurements and airborne hyperspectral and thermal remote sensing.
Our findings indicated that management treatments affected vegetation diversity, productivity and energy balance. Higher diversity plots had higher plant growth, albedo, canopy water content and lower surface temperature, indicating clear effects of management treatments on grassland ecosystem processes influencing surface–atmosphere feedbacks of mass and energy.
The coherent responses of multiple airborne remote sensing indices illustrate potential cobenefits of grassland restoration practices that enhance ecosystem productivity and biodiversity and mitigate climate change through surface–atmosphere feedbacks, offering a new strategy to address the challenges of biodiversity loss and climate change in grassland ecosystems.
... These complex dynamics, including key uncertainties, are illustrated in Fig. 1 (b), (c). These albedo trade-offs are rarely included in large-scale forest carbon assessments despite their growing policy relevance [27,29,37]. To address these gaps (summarized visually in Fig. 1(c)), we employ an integrated modeling approach using the Growth and Yield Projection System (GYPSY) [23] and the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) [24] to evaluate 250year carbon stock trajectories under various A/R scenarios in the Taiga Plains. ...
... Notably, our 250-year dual carbon-albedo assessment goes beyond prior studies that examined shorter time frames or considered only carbon sequestration [27,30]. By simulating ecosystem carbon dynamics alongside albedo-driven radiative forcing, we capture legacy effects and trade-offs that shorter or carbon-only analyses might miss. ...
The boreal forest plays a crucial role as a global carbon sink. This study uses two 250-year simulations of Canada's Taiga Plains, an area targeted by the 2 Billion Trees Program to evaluate afforestation and reforestation strategies that vary by species mix, planting density, and surface albedo. Medium density stands, 600 to 1400 trees per hectare, composed of mixed species with approximately 25 to 40 percent deciduous trees sequestered 15 to 30 percent more net ecosystem carbon than conifer monocultures. These benefits stem from a combination of rapid early growth, long-term carbon retention, and enhanced resilience to disturbance. Replanting understocked stands with such mixtures increased long-term carbon storage by 18 to 30 percent relative to prevailing scenarios. When surface albedo was considered, pure evergreen or deciduous stands showed a reduction in climate benefit by 6 to 20 percent, while mixed stands maintained net cooling and achieved the highest sequestration rates, approximately 4.6 to 4.7 tons of carbon dioxide equivalent per hectare per year. Scenarios involving partial harvesting followed by replanting sustained or improved ecosystem carbon stocks, about 300 to 340 tons of carbon per hectare, and productivity, roughly 1.6 to 2.0 tons of carbon per hectare per year, without increasing ecological risk. Overall, integrating fast-growing deciduous species with long-lived conifers at moderate planting densities enhances the climate mitigation potential of boreal afforestation and reforestation efforts and offers guidance for reforestation policy in similar high latitude ecosystems.
... One such activity is anthropogenic land use and land cover change (LULCC), manifested primarily as the loss of primary and secondary land (psl, either forested or non-forested) and the expansion of agricultural land, such as cropland, pasture and rangeland, in the recent centuries. LULCC influences the climate system biogeochemically by modifying the CO 2 concentration in the atmosphere 6 and biophysically by changing land surface properties 7 . The biophysical effects include direct effects and indirect effects. ...
... Our analyses demonstrate that historical LULCC alleviated such water crisis in these two regions to some extent (Fig. 4). Notably, this result cannot be misinterpreted as we encourage deforestation, as forests can provide many other services 6 . On the contrary, historical LULCC has decreased water availability in South Australia that is already facing water scarcity 47 , exacerbating the situation. ...
Anthropogenic land use and land cover changes (LULCC) have profound impacts on land water availability, defined as precipitation (P) minus evapotranspiration (ET), through biophysical pathways. However, such impacts have long been debated mostly due to either the inadequate consideration of the atmospheric feedbacks arising from the changes in circulations and background climate in observation-based studies or unrealistic representation of historical LULCC in idealized-simulation-based studies. To overcome these limitations, we use the latest simulations from multiple Earth system models to investigate the impacts of historical (1850-2014) and future (2015-2100) LULCC on P–ET. Here we show that historical LULCC caused an insignificant reduction in global P–ET, mainly in wet regions. Locally, P–ET tends to decrease (increase) in deforestation (reforestation) regions mainly due to the dominant role of precipitation. Approximately 3.8% of the global land area (5.1 Mkm2) even has experienced opposite regime shifts, in which negative (positive) P–ET becomes positive (negative). Under a medium-to-high warming scenario, however, reforestation is projected to decrease P–ET even over reforested areas. This study not only elucidates the hydrological effects of realistic LULCC with atmospheric feedbacks being fully considered, but also highlights that the relative importance of the local effects and atmospheric feedbacks varies with background climate changes. We stress that background climate changes and feedbacks due to LULCC should be considered when planning reforestation and other land-use policies.
... Land surface albedo modulates the amount of energy that the Earth absorbs from the Sun, and it is thus a key variable influencing surface temperature and water balance [11][12][13][14][15] . The anthropogenic intensification of land use or land cover (LULC) and the continuing climate change are profoundly altering landscape characteristics and land physical processes, ultimately causing large changes in surface albedo [1][2][3] , which directly alter the Earth's radiation budget. ...
... To explain the reasons for albedo changes in non-conversion regions, a multivariate linear regression model (equation (13)) is used to fit monthly shortwave albedo changes in each pixel from MCD43A3 C6.1 (Extended Data Fig. 1c where ε represents the model residuals, NDVI 51 was defined in the main text, and SSI and NMDI denote the spectral shape index 33 and the normalized multi-band drought index 34 , respectively. NDVI, SSI and NMDI are used to characterize the PV cover, NPV cover and SWC, respectively. ...
Surface albedo greatly affects how much energy the Earth absorbs. Intensive human activities and accelerated climate change have altered surface albedo across spatial and temporal scales1, 2–3, yet assessments of the effects of land use or land cover (LULC) and snow variations on land surface albedo are scarce at the global scale. As a result, the global land surface albedo dynamics over recent decades and their corresponding radiative forcing to the climate system remain poorly understood4, 5, 6, 7, 8–9. Here we quantify the individual and combined effects of snow cover dynamics, LULC conversions and non-conversion regions on albedo variations during 2001–2020 and estimate their induced radiative forcing. We show that the negative radiative forcing induced by the global land surface albedo change was −0.142 (−0.158, −0.114) W m⁻² over the past two decades. The global snow-free land surface albedo increased by 2.2% (P < 0.001), with a negative radiative forcing of −0.164 (−0.186, −0.138) W m⁻² (P < 0.001). The magnitude of this negative forcing is sevenfold larger than the positive forcing induced by snow dynamics, and equivalent to 59.9% of that caused by CO2 emissions from 2011 to 2019¹⁰. The global radiative forcing due to albedo changes in LULC non-conversion regions is 3.9 to 8.1 times greater than that from LULC conversions. The radiative forcing induced by albedo changes highlights the important role of land surface dynamics in modulating global warming.
... Forests cover more than 31% of the Earth's surface and have a crucial role in the global water and energy cycles (Bonan, 2008). Transpiration, which is the primary way for plants to release water through stomata into the atmosphere, influences the local climate and precipitation patterns (Bonan, 2015;Ellison et al., 2017). ...
... Transpiration, which is the primary way for plants to release water through stomata into the atmosphere, influences the local climate and precipitation patterns (Bonan, 2015;Ellison et al., 2017). It also significantly affects biogeochemical cycles and other forest characteristics (Bonan, 2008;Jasechko et al., 2013;Schlesinger & Jasechko, 2014;K. Wang & Dickinson, 2012). ...
Forests significantly influence regional and global water cycles through transpiration, which is affected by meteorological variables, soil water availability, and stand and site characteristics. Variable retention harvesting (VRH) is a forest management practice in which varying densities of trees, such as 55% and 33%, are retained after thinning or harvesting. These trees can be grouped together or evenly distributed. VRH aims to enhance forest growth, improve biodiversity, preserve ecosystem functions, and generate economic revenue from harvested timber. Application of VRH treatment in forest ecosystems can potentially impact the response of forest transpiration to environmental controls. This study analyzed the impacts of four different VRH treatments on sap flow velocity (SV) in an 83‐year‐old red pine (Pinus resinosa Ait.) plantation forest in the Great Lakes region in Canada. These VRH treatments included 55% aggregated (55A), 55% dispersed (55D), 33% aggregated (33A), and 33% dispersed (33D) basal area retention, and an unharvested control (CN) plot, 1 ha each. Analysis of counterclockwise hysteresis loops between SV and meteorological variables showed larger hysteresis areas between SV and photosynthetically active radiation (PAR) than vapor pressure deficit (VPD) and air temperature (Tair), particularly in clear sky and warm temperatures in the summer. It demonstrated that PAR was the primary control on SV across VRH treatments, followed by VPD and Tair. Larger hysteresis loop areas and higher SV values were observed in the CN and 55D treatments, with lower values found in the 55A, 33D, and 33A plots. This suggests that maintaining dispersed retention of 55% basal area (55D) is the optimal forest management practice that can be utilized to enhance transpiration and forest growth. These findings will assist forest managers and other stakeholders to adopt sustainable forest management practices, thereby enhancing forest growth, water use efficiency, and resilience to climate change. Additionally, these practices will contribute to nature‐based climate solutions.
... Vegetation plays a crucial role in ecosystems by releasing oxygen and absorbing carbon dioxide through photosynthesis, thereby regulating atmospheric composition and mitigating climate change [1][2][3]. Moreover, vegetation cover protects soil, reduces erosion, enhances soil fertility, and supports water cycling by aiding groundwater recharge [4,5]. ...
... Additionally, future FVC trends were projected by integrating climate scenario predictions with interaction analyses of driving mechanisms. The objectives of this study were 1 ⃝ to analyze the spatiotemporal dynamic characteristics of FVC in southwestern China; 2 ⃝ to determine the driving mechanism of FVC dynamics; 3 ⃝ to project future FVC trends under various climate change scenarios. The findings in our study provide a comprehensive understanding of the evolutionary patterns of FVC, their driving mechanisms, and FVC trends in future in southwestern China. ...
As a well-known ecological vulnerability region, monitoring and studying vegetation dynamics in southwestern China is important for resource management, ecological conservation, and climate adaptation strategies. The spatiotemporal dynamic characteristics of fractional vegetation cover (FVC) in southwestern China during the early 21st century was analyzed using MODIS Enhanced Vegetation Index (EVI) data. Additionally, this study employed the Geographic Detector Model (GDM), an innovative spatial statistical tool, to analyze the driving mechanism of FVC spatial patterns. The results indicated as follows: (1) the overall FVC in southwestern China exhibited a slight increasing trend, with distinct spatial heterogeneity; (2) the combined impacts of climate change and human activity could be the primary drivers of FVC changes, with relative contribution of 37.75% and 62.25%, respectively; (3) elevation was recognized as the key factor influencing this spatial variability, influencing hydrothermal conditions, vegetation types, soil types, and human activity intensity; (4) FVC increases steadily under high-emission scenarios of SSP370 and SSP585 from 2030 to 2100, while it exhibits an “increase–decrease” pattern under the low-emission scenarios of SSP126 and SSP245 from 2030 to 2100, with shifts occurring in 2080 and 2090, respectively. This pattern may result from the combined effects of moderate warming and fluctuations in precipitation, where initial hydrothermal conditions promote vegetation growth, but subsequent changes potentially inhibit it.
... Forests are pivotal in sustaining global biogeochemical cycles and ecosystem services such as carbon sequestration and biodiversity conservation (Bonan, 2008;Y. Pan et al., 2013). ...
Atmospheric nitrogen (N) deposition affects soil nitrate (NO3– {{\text{NO}}_{3}}^{\mbox{--}}) dynamics in forests, yet mechanisms driving NO3– {{\text{NO}}_{3}}^{\mbox{--}} accumulation in semi‐arid regions remain unclear. Here, we quantified atmospheric and microbial contributions to soil NO3– {{\text{NO}}_{3}}^{\mbox{--}} by analyzing ¹⁷O anomalies in 26 semi‐arid forests under high N deposition in northern China. Heavier N‐polluted temperate forests showed lower ¹⁷O anomalies in soil NO3– {{\text{NO}}_{3}}^{\mbox{--}} (1.0‰ ± 0.8‰), indicating lower atmospheric contributions (4.2% ± 3.2%), but higher atmospheric concentrations (0.3 ± 0.3 mg N kg⁻¹) and microbial nitrification rates (459.7 ± 225.4 kg N ha⁻¹ yr⁻¹). Both contribution and concentration of atmospheric NO3– {{\text{NO}}_{3}}^{\mbox{--}} in soils increased with NO3– {{\text{NO}}_{3}}^{\mbox{--}} inputs, whereas nitrification rate positively correlated with N deposition independent of precipitation, suggesting deposited N pollutants rather than water as a main driver of soil NO3– {{\text{NO}}_{3}}^{\mbox{--}} production and accumulation. These findings are important for understanding sources and accumulation of NO3– {{\text{NO}}_{3}}^{\mbox{--}} in temperate forests under N deposition.
... Forest ecosystems play a key role in the terrestrial carbon cycle, storing approximately 45% of terrestrial carbon and acting as long-term carbon sinks [1,2]. They also support essential ecosystem services, and are an important part of nature-based solutions in the context of anthropogenic climate change, in line with the Paris Agreement and global carbon neutrality goals [3]. ...
As enduring carbon sinks, forest ecosystems are vital to the terrestrial carbon cycle and help moderate global warming. However, the long-term dynamics of aboveground carbon (AGC) in forests and their sink-source transitions remain highly uncertain, owing to changing disturbance regimes and inconsistencies in observations, data processing, and analysis methods. Here, we derive reliable, harmonized AGC stocks and fluxes in global forests from 1988 to 2021 at high spatial resolution by integrating multi-source satellite observations with probabilistic deep learning models. Our approach simultaneously estimates AGC and associated uncertainties, showing high reliability across space and time. We find that, although global forests remained an AGC sink of 6.2 PgC over 30 years, moist tropical forests shifted to a substantial AGC source between 2001 and 2010 and, together with boreal forests, transitioned toward a source in the 2011-2021 period. Temperate, dry tropical and subtropical forests generally exhibited increasing AGC stocks, although Europe and Australia became sources after 2011. Regionally, pronounced sink-to-source transitions occurred in tropical forests over the past three decades. The interannual relationship between global atmospheric CO2 growth rates and tropical AGC flux variability became increasingly negative, reaching Pearson's r = -0.63 (p < 0.05) in the most recent decade. In the Brazilian Amazon, the contribution of deforested regions to AGC losses declined from 60% in 1989-2000 to 13% in 2011-2021, while the share from untouched areas increased from 33% to 76%. Our findings suggest a growing role of tropical forest AGC in modulating variability in the terrestrial carbon cycle, with anthropogenic climate change potentially contributing increasingly to AGC changes, particularly in previously untouched areas.
... Forests and climate are fundamentally connected: the disappearance or degradation of forests is both a cause and a consequence of climate change. [2]. ...
Deforestation is a pressing environmental issue, and assessing forest loss with precision is crucial for effective conservation strategies. This study evaluates forest area loss in the Special Nature Reserve "Gornje Podunavlje" over a seven-year period from July 2017 to July 2024. Utilizing remote sensing data from PlanetScope, Sentinel-2, and Landsat-8 satellites, the study employs the XGBoost machine learning classifier to classify forest cover. Results indicate a consistent decline in forest area across all datasets, with reductions from approximately 43 km² in July 2017 to around 33 km² by July 2024. Despite variations in reported forest area due to differences in spatial resolution-PlanetScope (3 meters), Sentinel-2 (10 meters), and Landsat-8 (30 meters)-the overall trend of forest loss is evident. Landsat-8 consistently reported higher forest area compared to PlanetScope and Sentinel-2, attributed to its coarser resolution which may include more edge effects. The high-resolution PlanetScope data allowed for more precise delineation of forest boundaries, enhancing the accuracy of forest cover assessments.
... Climate models predict that droughts are likely to increase in frequency and severity in many regions worldwide (Dai 2012;Petrova et al. 2024). Over the past few decades, droughts have reduced tree growth and killed trees in tropical, temperate, and boreal forests (Allen et al. 2010;Hammond et al. 2022;Sterck et al. 2024), leading to changes in community structure (Saura-Mas et al. 2015), species distribution (Anderegg 2015), biogeochemical cycles (Bonan 2008), and ecosystem functioning . The carbon sequestration capacity of tropical and temperate forests has also been severely reduced by during drought events Doughty et al. 2015), which may further exacerbate the frequency and intensity of droughts (Trenberth et al. 2014;Bauman et al. 2022). ...
Climate change has significantly increased the frequency and severity of droughts and risk of tree death worldwide. Differences in leaf habit, plant size, and species diversity are associated with differences in the risk of drought-induced mortality, but the relative contributions of these factors to the risk of mortality are unclear. In a study of the mortality of tree and shrub species during the extreme drought of 2019 in a savanna ecosystem in Southwest China, we assessed the relative contributions of evergreen and deciduous leaf habit, plant size, and species richness and diversity to the mortality of shrubs and trees after the 2019 extreme drought. The deciduous species had significantly lower hydraulic safety margins than the coexisting evergreen species, resulting in a higher mortality risk. Additionally, species and individuals with taller canopies tended to have deeper root systems, an advantage during extreme drought that reduced mortality risk. Notably, mortality risk was largely independent of stand species richness and diversity. Overall, leaf habit and plant height were better predictors of mortality risk than species richness and diversity. These novel insights provide a better understanding of the mechanisms driving drought-induced mortality in the ecosystems with a low canopy and weak interspecific and intraspecific competition for shared resources. Leaf habit and tree size should be incorporated into hypotheses on the mechanisms underlying drought-induced tree mortality.
... While the BGP effects of land-based CDR on global temperature are still subject to ongoing research, such effects are reported to depend on the scale and type of CDR deployment and the resulting modification of the Earth's surface energy balance. In addition to the potential of land-based CDR techniques such as forestation, bioenergy crop cultivation, and soil carbon sequestration practices to alter surface characteristics such as albedo, energy partitioning, evapotranspiration, and surface roughness (Bonan, 2008;Jackson et al., 2008;Betts, 2000;Buechel et al., 2024), these modifications could lead to potential global and regional temperature changes (Cheng et al., 2024;Windisch et al., 2021;Cerasoli et al., 2021) -in some cases even beyond where the LUC is implemented (De Hertog et al., 2023;Winckler et al., 2019a). Such changes in BGP processes can impact local and potentially global temperatures, with effects shown to vary with latitude and regional characteristics, such as instances where reforestation leads to decreased albedo and increased evapotranspiration, affecting cloud cover and regional temperatures with latitudinal dependence (Bright et al., 2017;Arora and Montenegro, 2011). ...
Anthropogenic land-use change (LUC) substantially impacts climate dynamics, primarily through modifications in the surface biogeophysical (BGP) and biogeochemical (BGC) fluxes, which alter the exchange of energy, water, and carbon with the atmosphere. Despite the established significance of both the BGP and BGC effects, their relative contribution to climate change remains poorly quantified. In this study, we leveraged data from an unprecedented number of Earth system models (ESMs) of the latest generation that contributed to the Land Use Model Intercomparison Project (LUMIP), under the auspices of the Coupled Model Intercomparison Project Phase 6 (CMIP6). Our analysis of BGP effects indicates a range of global annual near-surface air temperature changes across ESMs due to historical LUC, from a cooling of -0.23 °C to a warming of 0.14 °C, with a multi-model mean and spread of -0.03±0.10 °C under present-day conditions relative to the pre-industrial era. Notably, the BGP effects indicate warming at high latitudes. Still, there is a discernible cooling pattern between 30° N and 60° N, extending across large landmasses from the Great Plains of North America to the Northeast Plain of Asia. The BGC effect shows substantial land carbon losses, amounting to -127±94 Gt C over the historical period, with decreased vegetation carbon pools driving the losses in nearly all analysed ESMs. Based on the transient climate response to cumulative emissions (TCRE), we estimate that LUC-induced carbon emissions result in a warming of approximately 0.21±0.14 °C, which is consistent with previous estimates. When the BGP and BGC effects are taken together, our results suggest that the net effect of LUC on historical climate change has been to warm the climate. To understand the regional drivers (and thus potential levers to alter the climate), we show the contribution of each grid cell to LUC-induced global temperature change, as a warming contribution over the tropics and subtropics with a nuanced cooling contribution over the mid-latitudes. Our findings indicate that, historically, the BGC temperature effects dominate the BGP temperature effects at the global scale. However, they also reveal substantial discrepancies across models in the magnitude, directional impact, and regional specificity of LUC impacts on global temperature and land carbon dynamics. This underscores the need for further improvement and refinement in model simulations, including the consideration and implementation of land-use data and model-specific parameterizations, to achieve more accurate and robust estimates of the climate effect of LUC.
... The interplay between forests, biodiversity, and the climate also adds to this complexity. Pan et al. (2011) and Bonan (2008) provided studies that support the argument that safeguarding and even growing forest cover can go a long way to offset fossil fuel emissions and deforestation. The studies reveal the need to enforce reforestation and conservation strategies to improve land use and restore the ecological equilibrium affected by climate change. ...
There is a sharp inclination to use green energy sources such as solar, hydro, and nuclear energy to accomplish the COP29 targets
and sustainability goals. The current study attempts to explore the role of green solar, hydro, and agriculture land use apropos
global pollutant emissions. In doing so, the study examines the impacts of agricultural land use, forest area, and urbanization
on global emissions. The study uses the global historical data from 1990Q1 to 2021Q4. The authors employ the diagnostic tests,
autoregressive distributed lag models, and causality analysis for empirical analysis. The autoregressive distributed lag model's
results mentioned that agricultural land and forestry also help improve environmental sustainability and urban landscape in the
short and long run. In addition, the results find linear and nonlinear impacts of green solar and nuclear energy to mitigate the
global carbon emission levels. The structural change policies of industrialization and urbanization remain the critical obstacles
to attaining environmental sustainability. The on-hand
research contributes to the ongoing challenges faced by global economies
regarding green energy sources, agriculture land management and their criticality in attaining a sustainable environment by
reducing carbon emissions. The research recommends further investments in green solar, agriculture land management, and
incentivizing clean energy sources to achieve sustainable global development.
... The S2-C1 and S2-C5 models perform comparably to PML-V2 and GLEAM4 across all sites, and outperform MOD16A2GF (Table 5). In the continental, temperate, and tropical climates-where ET is strongly influenced by VPD, radiation, and LAI, and forest transpiration dominates (Bonan, 2008)-our optimized models slightly outperform the PML-V2. The S2-C5 model performs particularly well in tropical regions, where it exhibited a high correlation with uWUE ( Figure 10). ...
Dual‐source remotely sensed evapotranspiration (ET) models require accurate separation of soil evaporation (Es), plant transpiration (Ec), and precipitation interception (Ei) based on soil and canopy resistances. Despite the availability of several ET products and algorithms, comprehensive evaluations of resistance configurations remain scarce. This study systematically evaluates various combinations of five soil resistance methods, eight canopy resistance methods, and two precipitation interception algorithms within the Shuttleworth‐Wallace (S‐W) framework. Using eddy covariance data from 119 FLUXNET sites and the latest ET products, we find that the Ball‐Berry‐Leuning method, unified stomatal method, and RL empirical method provide comparable and top‐ranked performance across plant functional types (PFTs) and climate zones, with only a single free parameter calibrated by genetic algorithm. The power function method (S2), sensitive to soil surface water content proves to be the most effective for modeling Es, particularly in water‐limited regions. The performance of best‐performing but unexplored combinations (S2‐C1, S2‐C2, S2‐C5) is consistent with PML‐V2, GLEAM4, and underlying water use efficiency model, explaining 56% of the variation in daily ET and achieving an root mean square error as low as 1.02 mm day⁻¹. However, these models show reduced accuracy in arid zones, where prolonged water stress led to a 38% reduction in R². This highlights the need for a more accurate representation of soil moisture stress in arid regions, which is often overlooked in existing models. Our study offers robust, parsimonious, and broadly applicable models for ET estimation across PFTs and climate zones.
... Earth's forests currently serve as a substantial carbon sink, absorbing roughly a quarter of human carbon emissions annually from the atmosphere (Bonan 2008;Pan et al. 2011;Pugh et al. 2019). Alongside critical and necessary efforts to dramatically reduce fossil fuel emissions, forests can contribute to climate change mitigation as "nature-based climate solutions" (NbCS), which are a suite of potential changes in management decisions to increase forest carbon stocks (Griscom et al. 2017;Nolan et al. 2021;Seddon 2022). ...
Nature‐based climate solutions in Earth's forests could strengthen the land carbon sink and contribute to climate mitigation, but must adequately account for climate risks to the durability of carbon storage. Forest carbon offset protocols use a “buffer pool” to insure against disturbance risks that may compromise durability. However, the extent to which current buffer pool tools and allocations align with current scientific data or models is not well understood. Here, we use a tropical forest stand biomass model and an extensive set of long‐term tropical forest plots to test whether current buffer pool contributions are adequate to insure against observed disturbance regimes. We find that forest age and disturbance regime both influence necessary buffer pool sizes. In the majority of disturbance scenarios in a major carbon registry buffer pool tool, current buffer pools are substantially smaller than required by carbon cycle science. Buffer pool tools and estimates urgently need to be updated to accurately assess disturbance regimes and climate change impact on disturbances based on rigorous, open scientific datasets for nature‐based climate solutions to succeed.
... Increased temperatures and extended periods of drought weaken trees, making them more vulnerable to diseases and insect outbreaks (Allen et al., 2010). Additionally, deforestation and habitat loss worsen carbon emissions, diminishing the capacity of forests to function as carbon sinks (Bonan, 2008). To combat climate-related forest degradation, it is essential to implement conservation strategies such as afforestation, reforestation, and sustainable forest management. ...
Climate change is a critical global issue affecting ecosystems and biodiversity. Rising temperatures, shifting precipitation patterns, and extreme weather events disrupt habitat stability and ecological interactions. Key contributors to climate change include greenhouse gas emissions from fossil fuel combustion, deforestation, and industrial activities. Both terrestrial and aquatic ecosystems face significant threats, including habitat degradation, species migration, wildfires, ocean acidification, and coral bleaching. The consequences extend beyond biodiversity loss, impacting carbon sequestration, water resources, and food security. Rising sea levels threaten coastal habitats, while shifts in species distribution disrupt ecosystems and food chains. Addressing climate change requires urgent mitigation and adaptation efforts. Mitigation strategies focus on reducing emissions through renewable energy, sustainable land use, and carbon sequestration. Adaptation measures enhance ecosystem resilience through conservation, habitat restoration, and climate-smart policies. A comprehensive approach integrating these strategies is essential to ensure environmental sustainability and protect future generations.
... Changes in the seasonal variability in rainfall patterns across the tropics have also been observed (Feng et al., 2013;Fu et al., 2013;Fu, 2015). Tropical forests mitigate climate change not only by absorbing nearly half of fossil fuel emissions (Pan et al., 2024) but also through their key role in the global water cycle (Bonan, 2008). About 40 % of the global land precipitation is estimated to originate from evapotranspiration (Ellison et al., 2017), which is regulated by vegetation cover. ...
This review of recent advances in biosphere research aims to provide information on eight selected themes related to changes in biodiversity, ecosystem functioning, social and economic interactions with ecosystems, and the impacts of climate change on the biosphere. An interdisciplinary panel of experts selected these eight themes from a public survey based on relevance and scientific evidence that have the potential to guide future actions as well as inspire future research questions. Our focus is on the interactions between climate, biosphere, and society and on strategies to sustain, restore, or promote ecosystems and their services. The themes focus on innovative opportunities for coastal habitats, forest linkages to droughts, and increasing fire risks. We further discuss nature-based carbon dioxide removal (CDR) implementation risks and the share of (semi-)natural habitats in the landscape. Finally, we highlight the importance of comprehensive international policy packages and the social–economic value of ecosystems in the future and present the idea of convivial conservation. Based on an analysis of these eight topics, we have synthesized four overarching insights: (i) improve mechanisms of inclusive decision-making, (ii) establish and strengthen incentives for sustainable practices, (iii) measure and share regional features, and finally (iv) adopt long-lasting holistic landscape management strategies. This review emphasizes that the interlinked challenges for ecosystems, including the socio-economic dimensions, require interdisciplinary and integrative approaches to develop effective and sustainable solutions.
... Recent studies have indicated that the implementation of the national ecological restoration projects has improved ecosystem services such as soil erosion control Ouyang et al. 2014), water retention and flood mitigation (Ouyang et al. 2016), and biodiversity conservation (Ouyang et al. 2014;Wang et al. 2016). In addition, a series of management practices employed under the framework of these restoration projects-including afforestation, reforestation (shelter forests, forest protection, and sand control), forest tending (forest protection and sand control), transforming cropland into forest (GfG), reducing timber harvesting (forest protection), and fencing in grasslands (grassland conservation)-can increase forest area, prevent carbon loss from vegetation and soil, and subsequently increase carbon stocks and sinks (Xu et al. 2017;Bonan 2008). In this chapter, two of China's six large-scale national restoration projects will be described in detail: the Three-North Shelter Forest Programme (TNSFP) and the Grain for Green Programme (GfG) (Fig. 27.1). ...
Since the late 1970s, China has launched six national ecological restoration projects across the country to protect the environment and restore degraded ecosystems. The implementation of these national ecological restoration projects has improved ecosystem services such as soil erosion control, water retention, flood mitigation, and biodiversity conservation. As China’s first world super ecological engineering project, the Three-North Shelter Forest Programme has achieved excellent results regarding maintaining national ecological security as well as promoting economic and social development. In addition, the Grain for Green Programme (GfG) is the ecological engineering project with the largest investment, the strongest policy, the widest coverage, and the highest degree of public participation in the world. The implementation of GfG has greatly increased the average forest coverage rate in the project area and significantly improved the soil erosion situation in major river basins as well as around important lakes and reservoirs.
... Plant photosynthesis is the primary driver of terrestrial carbon uptake that determines ecosystem gross primary productivity (GPP). Tropical rainforests, which store nearly half of global forest carbon and play a vital role in regulating global carbon and water cycles, are increasingly threatened by extreme droughts and heatwaves and may potentially turn into carbon sources due to increased tree mortality (Bonan, 2008;Phillips et al., 2009;Pan et al., 2011;Brienen et al., 2015;Aleixo et al., 2019;Chen et al., 2024). However, uncertainty in models of carbon uptake remains significant in the tropics, disrupting accurate predictions of ecosystem responses to environmental change (Huntzinger et al., 2017;Melnikova et al., 2024). ...
Recent studies have shown a linear relationship between solar‐induced Chl fluorescence (SIF) and gross primary productivity (GPP) at large scales. However, this relationship diverges at finer leaf scales, particularly in tropical forests with complex canopy structures.
To address this issue, we assessed seasonal and intracanopy variations in leaf energy partitioning in central Amazonian forests with extensive in‐canopy sampling and pulse‐amplitude‐modulated Chl fluorescence measurements. We explored the pathways of photon utilization for photochemistry (ΦPSII), heat dissipation (ΦNPQ), and nonregulated quenching (ΦNO) of fluorescence.
We found consistent increases in ΦNPQ and decreases in ΦPSII and ΦNO with increasing canopy height, primarily driven by changes in photosynthetically active radiation. During the dry season, a triphasic relationship between ΦNO and ΦPSII was detected, alternating between positive and negative relationships across leaf irradiance levels, highlighting stress‐induced physiological responses. Interspecific variation and vapor pressure deficit also played significant roles in modulating ΦNO, emphasizing the complex interaction between environmental factors, species composition, and energy dissipation across canopy strata.
These insights into leaf‐level fluorescence and energy dynamics show the complex mediation of ΦNPQ‐ΦNO‐ΦPSII relationships, offering implications for enhancing SIF‐GPP relationships and understanding tropical forest responses to climate change.
... Indonesia's forests are of global significance; they are considered among the world's most biodiverse (Mittermeier et al. 1998;Myers et al. 2000), and provide critical climate benefits by sequestering carbon and regulating regional hydrological and atmospheric cycles (Bonan 2008). They also play an important role in supporting human well-being; it is estimated that 37% of Indonesia's poor live within 10 km of a forest boundary (Rakatama and Pandit 2020;Sunderlin et al. 2005), with ~60 million people residing within 1 km of a state forest (Kraus et al. 2021). ...
... To mitigate climate change, countries have submitted Nationally Determined Contributions (NDCs) with sector-specific reduction targets, emphasizing the role of forests as carbon sinks. However, forests are increasingly impacted by climate change, including droughts and extreme precipitation, which alter their physical, chemical, and biological processes [3]. Consequently, maximizing forest functions-such as carbon sequestration, water resource enhancement, and disaster prevention-through adaptation strategies that reflect their environmental and ecological characteristics is crucial [4]. ...
This study aimed to analyze changes in water retention conservation in response to climate change and forest management strategies and to propose methods for securing sustainable water resources. The KO-G-Dynamic model, a Korean forest growth model, was utilized alongside aboveground and belowground water resource prediction models to evaluate changes in water retention conservation under various climate change scenarios and forest management strategies. The analysis revealed that under climate change and current forest management levels, water retention conservation was projected to reach 37.553 billion tons per year in the 2030s, 38.274 billion tons per year in the 2050s, and 40.306 billion tons per year in the 2080s. Under optimal forest management policies, the water yield and storage were expected to increase to 37.863 billion tons per year in the 2030s, 38.877 billion tons per year in the 2050s, and 41.495 billion tons per year in the 2080s. Notably, watershed-based forest management offers a more practical management unit than conventional legal boundaries, as it reflects hydrological flow and the ecological characteristics of forest environments. Furthermore, the watershed-based forest management scenario demonstrated greater feasibility in securing water resources. This study provides foundational data for climate change adaptation and sustainable forest management and may aid national and local forest planning. The findings underscore the critical role of forest management in mitigating climate change impacts and ensuring long-term water sustainability.
... This climatic change, which includes increasing temperatures and more extended drought periods, reshapes wildfire regimes (Thom and Seidl 2016;Descals et al. 2022), one of the major natural disturbances affecting boreal forest ecosystems (De Groot et al. 2013). Increased fire frequency, intensity, and severity (Flannigan et al. 2009;Keeley 2009;Abatzoglou et al. 2018) are consequently threatening to convert boreal forest soils, typically C sinks, into C sources (Bond-Lamberty et al. 2007;Bonan 2008;Walker et al. 2019). ...
Purpose
Our study investigates how low-intensity surface fires affect the concentration of dissolved organic carbon (DOC) and the quality of dissolved organic matter (DOM) in boreal forest soils. DOC, a crucial and labile carbon (C) pool, is highly sensitive to disturbances such as wildfires, yet its post-fire dynamics remain poorly understood in boreal ecosystems. By examining the immediate effects of these fires on DOM content and composition our research aims to deepen our understanding of soil carbon cycling and stability in a rapidly warming boreal region.
Methods
We compared DOC concentrations, δ¹³CDOC isotope composition, and DOM ultraviolet–visible absorbance properties from soil water collected in burned and unburned control plots during the first growing season following a low-intensity prescribed burning in a Finnish boreal Scots pine forest.
Results
The low-intensity surface fire removed aboveground vegetation and partially burned the organic topsoil, creating a layer of pyrogenic materials. In burned soils, while total soil C stocks remained unchanged, DOC concentration decreased, and DOC showed an enrichment in ¹³C, compared to DOC from unburned soils. This shift likely results from the loss of soluble C, reduced microbial biomass, and the addition of newly formed pyrogenic C. Burned soils also displayed DOM with higher aromaticity and molecular weight, suggesting a more stable and recalcitrant C pool in the soil water of fire-affected areas.
Conclusion
Our results highlight that low-intensity surface fires immediately alter soil DOM content and chemical composition in boreal forests, thereby affecting DOC fluxes within soils and to adjacent aquatic ecosystems. These post-fire DOC dynamics have implications for freshwater quality and regional carbon budgets. Considering the role of low-intensity fires as a major natural disturbance in the boreal forests of Northern Europe, their role and implications should be integrated into forest management strategies to help regulate DOC levels in surface waters.
... Consequently, many trees have died (Hartmann et al., 2018). Forests are responsible for two-thirds of global photosynthesis (Giri, 2017) and cover over a third (43%) of the Earth's land surface (Bonan, 2008;Karnosky, 2003). While forests are directly exposed to the effects of climate change, they are also impacted by this phenomenon in other ways. ...
Introduction
Climate change has led to rising atmospheric CO 2 levels and temperatures, projected to double CO 2 concentrations and increase temperatures by 2–5°C by the end of the 21 st century. These environmental changes influence plant primary and secondary metabolism, potentially altering plant-insect interactions. Herbivore performance depends on the nutritional quality of host plants, which may decline with elevated CO 2 due to an increased carbon-to-nitrogen (C:N) ratio. To explore these effects, the performance of spongy moth larvae ( Lymantria dispar ) was assessed on oak ( Quercus robur ) and spruce ( Picea abies ) seedlings grown under varying climatic conditions. This approach compares a preferred host with a non-preferred one in the case of L. dispar , providing insight into how host plant selection may be influenced under future climate scenarios. In addition, the nun moth ( Lymantria monacha ), a conifer-feeding species, was also studied on the experimental spruce seedlings to facilitate a comparison with a specialist herbivore.
Methods
Three-year-old oak and spruce seedlings were reared for 1 year under four climate scenarios combining two CO 2 levels (ambient: 410 ppm and elevated: 820 ppm) and two temperature regimes (20:15°C and 25:20°C). Seedlings were then processed into leaf powder diets for laboratory bioassays with larvae. Secondary metabolites in the seedlings were analyzed to assess climate-induced changes in tree composition and their effects on herbivores.
Results
Elevated CO 2 increased the C:N ratio in both tree species, with spruce showing a higher ratio than oak. Higher temperatures led to increased nitrogen content, particularly in oak seedlings. L. dispar performed better on oak despite higher secondary metabolite concentrations, while L. monacha exhibited minimal variation in performance on spruce across climate treatments.
Conclusion
The combined effects of elevated CO 2 levels and increased temperatures impacted plant quality; however, there were nearly no differences in the performance of Lymantria larvae. Despite the higher concentrations of secondary metabolites in the trees, the larvae were able to thrive effectively, demonstrating their resilience to environmental changes.
... Forests play a key role in the water cycle, as well as regulating surface temperatures and providing critical carbon sequestration services (Bonan, 2008). Although most forest types have low surface albedo, which can contribute to warmer surface temperatures, the evaporative cooling services provided by forest can help offset absorbed energy and are often not provided by alternative high-albedo, land-cover types. ...
The steady rise in global temperature as a result of human activity is causing changes in Earth’s water cycle. The balance of water stored within and moving between vapor, liquid, and frozen states in the water cycle is shifting, with consequences for water availability that include increases in drought, fire weather, flooding, and heavy precipitation, as well as cryosphere decline and sea-level rise. In this chapter of the U.S. Geological Survey Integrated Water Availability Assessment—2010–20, we provide an overview of climate-change observations and projections from Earth-system model simulations that relate to future water availability, from global and national climate assessments and from the published literature. Effects of climate change on primary water-cycle components are discussed in context of how global-scale hydroclimate drivers influence regional processes within the United States. Understanding the major climate drivers impacting the water cycle is crucial to predicting future changes in water availability and developing adaptation strategies to ensure human and ecosystem water supplies. First, we provide background information on the water cycle, the climate-model ensemble simulations developed to produce projections based on warming scenarios, and attribution and certainty levels. Tipping points, self-reinforcing feedbacks, cascading effects, and compound extremes are introduced. The framework of climatic impact drivers (CIDs) outlined in the Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC AR6) is used to show primary drivers of physical change to the water cycle and to understand and predict changes in future water availability. Specific climate-change related observations and projections are discussed for water cycle components of precipitation, evapotranspiration, soil moisture, streamflow, lakes and wetlands, ice and snow, and groundwater, as well as their implications for future water availability for humans and ecosystems. The chapter concludes with a synthesis discussion of three examples of complex regional-scale hydroclimate processes that influence water availability for populations in the United States, including (1) mountain and coastal precipitation, (2) aridification and drought, and (3) the influence of forest-cover change on terrestrial water-vapor recycling.
... The extensive application of NPs across various industries, including agriculture, has resulted in their increased presence in the environment, raising concerns regarding their potential impacts on forest ecosystems [6]. Forest trees, as integral components of terrestrial ecosystems, play crucial roles in carbon sequestration, biodiversity conservation, and climate regulation [7,8], and any adverse impacts on them can have cascading effects on broader ecosystem health and function [9,10]. For example, studies have demonstrated that NPs can infiltrate soil and water systems, where they interact with tree roots, potentially altering nutrient uptake, growth patterns, and physiological processes [11,12]. ...
Nanoparticles (NPs) are increasingly integrated into industrial and agricultural applications, yet their environmental impacts on forest ecosystems remain poorly characterized. Forest trees, as key components of global ecosystems, are both recipients and potential emitters of NPs, making forests critical but overlooked in the broader discussion of nanomaterial impacts. This review synthesizes current knowledge on NP interactions with forest ecosystems, focusing on their sources, pathways, transformations, and ecological consequences. NPs influence forest trees at molecular and physiological levels, with effects varying by type, size, concentration, and environmental context. While some NPs promote nutrient uptake, growth, and stress tolerance, others trigger oxidative stress and disrupt soil microbial communities and nutrient cycling. We highlight major knowledge gaps, including the lack of long-term field data and the limited understanding of NP impacts on soil fauna, microbial networks, and ecosystem processes. Furthermore, emerging applications of biodegradable and functionalized NPs for nutrient delivery, pest control, and genetic improvement are critically examined. This review underscores the urgent need for interdisciplinary research and regulatory frameworks to balance the benefits and risks of NPs in forestry. By integrating recent advances in nanotechnology and forest ecology, we propose strategies for harnessing sustainable NPs while safeguarding forest health and resilience amid escalating environmental pressures.
... Deforestation, in addition to releasing greenhouse gases, contributes to soil erosion, water pollution, and the loss of biodiversity, which can have devastating consequences for local communities and ecosystems (Bodo, Gimah, and Seomoni 2021). Also, the lack of forest vegetation affects the exchange of heat, moisture, and interactions between the land surface and the atmosphere; it also fragments the forest, which can degrade the forest ecosystem (Bonan 2008;Wang et al. 2016). ...
... This was also evident with significant correlations between the T estimates from WH-1 and WH-2 relative to WH-3. The ground surface was well irrigated and therefore would have lowered AT and increased RH closer to the ground, resulting in lowered energy exchange or ET demands [25,[47][48][49][50][51]. The T estimates pertinent to WMean would be better representative for accounting weather and energy exchanges at different canopy zones. ...
Precision irrigation requires reliable estimates of crop evapotranspiration (ET) using site-specific crop and weather data inputs. Such estimates are needed at high resolutions which have been minimally explored for heterogeneous crops such as orchards. In addition, weather information for estimating ET is very often selected from sources that do not represent conditions like heterogeneous site-specific conditions. Therefore, a study was conducted to map geospatial ET and transpiration (T) of a high-density modern apple orchard using high-resolution aerial imagery, as well as to quantify the impact of site-specific weather conditions on the estimates. Five campaigns were conducted in the 2020 growing season to acquire small unmanned aerial system (UAS)-based thermal and multispectral imagery data. The imagery and open-field weather data (solar radiation, air temperature, wind speed, relative humidity, and precipitation) inputs were used in a modified energy balance (UASM-1 approach) extracted from the Mapping ET at High Resolution with Internalized Calibration (METRIC) model. Tree trunk water potential measurements were used as reference to evaluate T estimates mapped using the UASM-1 approach. UASM-1-derived T estimates had very strong correlations (Pearson correlation [r]: 0.85) with the ground-reference measurements. Ground reference measurements also had strong agreement with the reference ET calculated using the Penman–Monteith method and in situ weather data (r: 0.89). UASM-1-based ET and T estimates were also similar to conventional Landsat-METRIC (LM) and the standard crop coefficient approaches, respectively, showing correlation in the range of 0.82–0.95 and normalized root mean square differences [RMSD] of 13–16%. UASM-1 was then modified (termed as UASM-2) to ingest a locally calibrated leaf area index function. This modification deviated the components of the energy balance by ~13.5% but not the final T estimates (r: 1, RMSD: 5%). Next, impacts of representative and non-representative weather information were also evaluated on crop water uses estimates. For this, UASM-2 was used to evaluate the effects of weather data inputs acquired from sources near and within the orchard block on T estimates. Minimal variations in T estimates were observed for weather data inputs from open-field stations at 1 and 3 km where correlation coefficients (r) ranged within 0.85–0.97 and RMSD within 3–13% relative to the station at the orchard-center (5 m above ground level). Overall, the results suggest that weather data from within 5 km radius of orchard site, with similar topography and microclimate attributes, when used in conjunction with high-resolution aerial imagery could be useful for reliable apple canopy transpiration estimation for pertinent site-specific irrigation management.
... Characterising the carbon and water fluxes of forest ecosystems is critical to understand biosphere-atmosphere interactions that drive many of the ecological, economic and social services forests provide to natural systems and humankind (Bonan, 2008). The Land Surface Temperature (LST) is a key parameter in all land surface processes (Anderson et al., 2008), and is well suited to monitor such interactions over forests since it depends on the functioning and health state of forests (e.g. ...
The Land Surface Temperature (LST) is well suited to monitor biosphere-atmosphere interactions in forests, as it depends on water availability and atmospheric/meteorological conditions above and below the canopy. Satellite-based LST has proven integral in observing evapotranspiration, estimating surface heat fluxes and characterising vegetation properties. Since the radiative regime of forests is complex, driven by canopy structure, components radiation properties and their arrangement, forest radiative temperatures are subject to strong angular effects. However, this depends on the scale of observation, where scattering mechanisms from canopy-to satellite-scales influence anisotropy with varying orders of magnitude. Given the heterogeneous and complex nature of forests, multi-angular data collection is particularly difficult, necessitating instrumen-tation distant enough from the canopy to obtain significant canopy brightness temperature and concurrent observations to exclude turbulence/atmospheric effects. Accordingly, current research and understanding on forest anisotropy at varying scales (from local validation level to satellite footprint) remain insufficient to provide practical solutions for addressing angular effects for upcoming thermal satellite sensors and associated validation schemes. This study presents a novel method founded in the optical remote sensing domain to explore the use of microcanopies that represent forests at different scales in the footprint of a multi-angular goniometer observing system. Both Geometric Optical (GO) and volumetric scattering dominated canopies are constructed to simulate impacts of anisotropy in heterogeneous and homogeneous canopies, and observed using a thermal infrared radiometer. Results show that heterogeneous canopies dominated by GO scattering are subject to much higher magnitudes of anisotropy, reaching maximum temperature differences of 3 • C off-nadir. Magnitudes of anisotropy are higher in sparse forests, where the gap fraction and crown arrangement (inducing sunlit/shaded portions of soil and vegetation) drive larger off-nadir differences. In dense forests, anisotropy is driven by viewing the maximum portion of sunlit vegetation (hotspot), where the soil is mostly obscured. Canopy structural metrics such as the fractional cover and gap fraction were found to have significant correlation with off-nadir differences. In more homogeneous canopies, anisotropy reaches a lower magnitude with temperature differences up to 1 • C, driven largely by volumetric scattering and components radiation properties. Optimal placement of instrumentation at the canopy-scale (more heterogeneous behaviour due to proximity to the canopy and small pixel size) used to validate satellite observations (more homogeneous behaviour due to larger pixel size) was found to be in cases of viewing maximum sunlit vegetation, for dense canopies. Given upcoming high spatial resolution sensors and associated validation schemes needed to benchmark LST and downstream products such as evapotranspiration, a better understanding of anisotropy over forests is critical to provide accurate, long-term and multi-sensor products. Fig. 1. Geometric optical (top) and volumetric (bottom) scattering mechanisms in forests, adapted from Jacob et al. (2008).
... Concern over tree restoration, however, has been expressed due to several climate-related factors including increased risk of drought and wild fire activity, shifts in regional water availability, as well as to biotic factor [8][9][10][11] . Furthermore, biogeophysical factors which include changes in surface energy fluxes (e.g., changes in surface albedo) can enhance or diminish the negative climate forcing associated with enhanced carbon sequestration [12][13][14][15][16][17][18][19][20] . Complete global afforestation or deforestation can also have a significant impact on climate through changes in large-scale atmospheric and oceanic circulation 21 . ...
Although tree restoration, including reforestation and afforestation, can enhance carbon sequestration and help mitigate climate change, this negative forcing can be strengthened or weakened through non-carbon cycle biogeophysical factors, including atmospheric chemistry. Here, we conduct climate modeling experiments with and without atmospheric chemistry driven by a high-end tree restoration scenario. Under both frameworks, the biogeophysical effects drive global mean warming due to surface darkening. This warming is muted in the Southern Hemisphere due to enhanced evapotranspiration. Furthermore, there is less warming—especially in the Southern Hemisphere—under interactive atmospheric chemistry, largely due to enhanced organic aerosol and cloud effects. Biogeophysical effects mute 45% of the biogeochemical cooling associated with enhanced land carbon storage, which decreases to 24% with atmospheric chemistry (including methane). Thus, higher climate change mitigation potential of tree restoration results from atmospheric chemistry effects, which are not usually considered.
... Forest's capacity of capturing and storing carbon through photosynthesis makes global forestation (afforestation and reforestation), an effective nature-based solution to curb climate change, complementing the efforts of greenhouse gas emission reduction [1][2][3][4] . Apart from its biochemical role in carbon cycling, forestation also affects local climate by directly modifying surface biophysical properties, such as albedo, roughness and evapotranspiration (ET) 5,6 . These biophysical feedbacks from forest change are often highly localized 7,8 , driven by a latitudinal counteraction between the radiative warming effect resulting from reduced albedo (dominant in boreal regions) and the turbulent cooling effect via increased ET and surface roughness (predominant in tropical latitudes) [9][10][11][12][13] . ...
Forestation is a proposed solution for mitigating global warming through carbon sequestration. However, its biophysical effects through surface energy modulation, particularly under rising CO2 levels, is less understood. Here we investigate the biophysical effects of global potential forestation on near-surface air temperature (Ta) under increasing CO2 concentrations using a land-atmosphere coupled model with slab ocean module. Our findings reveal that, under current climate conditions, the biophysical effect of global full-potential forestation can reduce land surface Ta by 0.062 °C globally. However, this cooling benefit diminishes as CO2 rises. While elevated CO2 slightly alters evaporative local cooling via stomatal closure and adjustments in forestation-driven rainfall regimes, the dominant reduction stems from non-local mechanisms. Background climate shifts reorganize forestation-induced horizontal temperature advection, weakening remote cooling in the Northern Hemisphere. These findings highlight the necessity of incorporating dynamic forest management strategies to optimize mitigation potential under a changing climate.
Solar-induced chlorophyll fluorescence (SIF) is a powerful tool for the estimation of gross primary productivity (GPP), but the relationship between SIF and GPP under drought stress remains incompletely understood. Elucidating the response of the relationship between SIF and GPP to drought stress is essential in order to enhance the precision of GPP estimation in forests. In this study, we obtained SIF in the red (SIF687) and far-red (SIF760) bands and GPP data from tower flux observations in a Chinese cork oak plantation to explore the response of the diurnal GPP-SIF relationship to drought stress. The plant water stress index (PWSI) was used to quantify drought stress. The results show that drought reduced SIF and GPP, but GPP was more sensitive to drought stress than SIF. The diurnal non-linear relationship of GPP-SIF (R2) decreased with the increase in drought stress, but a significant non-linear correlation remained for GPP-SIF (R2_GPP-SIF760 = 0.30, R2_GPP-SIF687 = 0.23) under severe drought stress (PWSIbin: 0.8–0.9). Physiological coupling strengthened the GPP-SIF relationship under drought, while canopy structure effects were negligible. Random forest and path analyses revealed that VPD was the key factor reducing the GPP-SIF correlation during drought. Incorporating VPD into the GPP-SIF relationship improved the GPP estimation accuracy by over 48% under severe drought stress. The red SIF allowed for more accurate GPP estimations than the far-red SIF under drought conditions. Our results offer important perspectives on the GPP-SIF relationship under drought conditions, potentially helping to improve GPP model predictions in the face of climate change.
Coastal wetlands are critical components of blue carbon ecosystems, yet the functional roles of benthic shellfish species in regulating sediment carbon dynamics are not yet fully elucidated. To address this knowledge gap, we investigated the effects of different shellfish zones—gastropods (Bullacta exarata, Umbonium thomasi) and bivalves (Mactra veneriformis, Meretrix meretrix, Potamocorbula laevis)—on sediment carbon fractions and microbial communities in representative intertidal wetlands of Liaodong Bay, China. We analyzed dissolved organic carbon (DOC), particulate organic carbon (POC), microbial biomass carbon (MBC), enzyme activities, and microbial genomic profiles, with particular emphasis on carbon fixation gene abundance within the top 0–10 cm of sediment. The results showed that POC and MBC levels in gastropod zones were 56.11% and 99.83% higher, respectively, than in bivalve zones, while carbon fixation gene abundance was 14.54% lower. Structural equation modeling (SEM) further revealed that shellfish type had a significant direct effect on MBC (λ = 0.824, p < 0.001). This study provides novel evidence that shellfish community composition regulates blue carbon storage through both biogeochemical and microbial pathways, highlighting the importance of species-specific management in shellfish aquaculture to enhance carbon sequestration. These findings offer a theoretical foundation for future assessments of coastal wetland carbon sinks and ecosystem service valuation.
Two reference materials (RMs) were developed at the National Institute for Environmental Studies (NIES) for biomonitoring atmospheric mercury (Hg). First-year pine needles (Pinus thunbergii), reflecting atmospheric conditions over approximately one year were collected from Nara and Ibaraki prefectures and designated as NIES RM No. 1001 Pine Needle I (PN I) and NIES RM No. 1002 Pine Needle II (PN II), respectively. After removing surface dust, the needles were oven-dried at 70 ℃, ground, homogenized, bottled, and sterilized using 60Co irradiation. Homogeneity and long-term stability tests were conducted for total Hg (THg) using cold-vapor atomic absorption spectrometry, confirming the material's suitability as RMs. The THg concentrations of PN I and PN II were 5.4 ± 0.4 ng/g and 22 ± 2 ng/g, respectively, lower than the NIST SRM 1575a Pine Needles (39.9 ± 0.7 ng/g). Given decreasing background levels of atmospheric Hg, precise measurement of low-concentration samples is increasingly important. Hg isotopic analysis was performed using a two-stage furnace or microwave-assisted digestion. Isotopic values for PN I were δ202Hg = –2.63 ± 0.24‰, Δ199Hg = –0.22 ± 0.17‰, Δ200Hg = –0.01 ± 0.10‰, and Δ201Hg = –0.19 ± 0.17‰ (2SD, n = 8), while those for PN II were δ202Hg = –1.64 ± 0.23‰, Δ199Hg = –0.51 ± 0.10‰, Δ200Hg = 0.00 ± 0.06‰, and Δ201Hg = –0.52 ± 0.13‰ (2SD, n = 12). Various trace element concentrations (Al, Ba, Ca, Cd, Cu, Fe, K, P, Rb, and Zn) were also measured. These candidate RMs are suitable for quality control in heavy metal and Hg isotope studies of foliage and similar matrices.
Phytolith carbon sequestration has been recognized as an important mechanism for long-term carbon sequestration in forest ecosystems. Conducting relevant research in cold temperate regions that are sensitive to climate change can reveal their unique mechanisms as a stable and long-term carbon pool, fill key blind spots in global carbon cycling models, and provide necessary scientific support for developing climate-resilient ecological strategies and carbon neutrality pathways. In this study, we focused on the Larix gmelinii forest ecosystem and investigated the latitudinal spatial characteristics of soil phytolith and phytolith-occluded carbon (phytOC) in Eastern China. We analyzed the factors that influenced their accumulation and assessed their storage potential across different climatic zones. Our findings revealed an exponential increase in soil phytolith content with increasing latitude in Eastern China. Additionally, the content of soil phytoliths in tropical and subtropical forests was significantly lower than in the cold temperate forests. It was also found that soil phytOC content increased linearly with latitude and was significantly higher in cold temperate zones than in the other climatic zones. The order of soil phytOC storage was tropical (0.23 t ha−1) < middle temperate (0.24 t ha−1) < subtropical (0.27 t ha−1) < cold temperate (1.20 t ha−1). Soil phytolith and phytOC content were significantly negatively correlated with temperature and precipitation. pH, organic matter, and nutrients of soil significantly influenced the formation and accumulation of soil phytoliths. It can provide a scientific basis for the quantitative evaluation of forest soil carbon pool.
West Africa is undergoing rapid agricultural intensification driven by population growth, leading to significant anthropogenic land use and land cover change (LCC), including both deforestation and afforestation. These changes can profoundly affect the regional climate system by altering the surface energy balance, moisture fluxes, and atmospheric circulation, potentially exacerbating the vulnerability of human, ecological, and economic systems. Despite the ability of climate models to simulate LCC impacts, considerable uncertainties remain, particularly in simulations of precipitation and temperature responses. This study provides the first multidisciplinary systematic review of LCC impacts in West Africa. Data from 26 selected publications were eventually synthesized from an initial pool of nearly 6000 studies. Results indicate that deforestation generally contributes to regional warming, with significant historical temperature increases of +0.26 ± 0.12 °C and projected increases of +0.88 ± 0.25 °C under the future scenarios. Conversely, afforestation could have significantly cooled the climate, lowering temperatures by −0.24 ± 0.14 °C historically and −0.22 ± 0.14 °C in future scenarios, without even accounting for carbon sequestration. Deforestation decreases regional precipitation by 80 ± 58 mm yr⁻¹ historically and −55 ± 102 mm yr⁻¹ in future scenarios, while large-scale afforestation could substantially reduce droughts with increased precipitation, averaging +40 ± 67 mm yr⁻¹ historically and 80 ± 58 mm yr⁻¹ in future scenarios. These results emphasize the need to integrate LCC-induced climate effects into land-based mitigation strategies, climate policy, and assessment frameworks.
Accurate estimation of canopy height is crucial for monitoring forest health, carbon cycling, biodiversity, and climate change. Existing canopy height mapping methods often integrate Global Ecosystem Dynamics Investigation (GEDI) LiDAR data with optical or radar remote sensing images. However, these methods typically establish relationships between single GEDI relative height (RH) metrics (e.g., RH95 or RH98) and surface reflectance or backscatter signals, overlooking valuable information from multiple RH metrics. In this study, we developed a multiple relative height metrics-based canopy height mapping (MRH-CHM) model, which was implemented using deep learning based on the Google Earth Engine (GEE) cloud platform. The MRH-CHM model integrates features from multiple GEDI RH metrics (e.g., RH0 to RH100 with an interval of 10 units) and also Landsat-8 and Sentinel-1 images. To deal with the distinct features in the multimodal data, in the proposed MRH-CHM method, the convolutional neural network (CNN) and multi-layer perceptron (MLP) modules were designed separately before a feature fusion process. Using the MRH-CHM model, a canopy height map of China for the year 2020 was produced at 30 m spatial resolution. The MRH-CHM results present greater accuracy than Lang’s, Potapov’s, and Liu’s products, achieving the lowest Root Mean Square Error (RMSE) of 5.74 m and the largest correlation coefficient (r) of 0.78 when validated against 6,168,244 hold-out GEDI validation data points. The produced map provides valuable scientific data for policymakers, researchers, and forest stakeholders to monitor forest health and biodiversity and to guide efforts toward carbon neutrality. The produced canopy height map is publicly available at https://doi.org/10.5281/zenodo.11560195.
Tropical forests are crucial for global climate regulation and carbon cycling. Mopane woodlands, a tropical dry forest covering southern Africa, feature high ecological-socioeconomic importance. In Mozambique, charcoal production is a major driver of Mopane degradation and aboveground carbon (AGC) loss. Accurate AGC estimation is essential for climate mitigation strategies. We applied machine learning techniques to predict stand-level AGC in Mopane woodlands across Mabalane and Chicualacuala districts, Gaza Province. Two evolutionary algorithms were tested: (1) a hybrid Genetic Algorithm and Random Forest (GARF), and (2) Genetic Programming (GP) using symbolic regression. In total, 139 predictor variables were derived from remote sensing, biophysical, and bioclimatic datasets. Field data included 114 cluster plots. Both algorithms reduced the dataset by 95.6%. Observed AGC ranged from 1.313 to 28.476 MgC ha⁻¹. GARF predictions ranged from 2.910 to 19.459 MgC ha⁻¹ (nRMSE = 0.427; MBE = 0.08), while GP showed a wider predictive range (1.721–23.503 MgC ha⁻¹; nRMSE = 0.428; MBE = 2.731×10⁻¹⁷). GARF relied on optical and bioclimatic variables, whereas GP operated independently of variable type. Both approaches were effective for feature selection and AGC prediction. However, GP produced a more interpretable model, offering advantages for replication and use in operational carbon inventories.
Exploring the synchronisation between radial growth from a specific tree species and the regional vegetation canopy growth covering a certain area (obtained from remote sensing data) and their climate responses contributes towards clarifying the influence of climate change on aboveground forest biomass. We assessed the variation and correlation between the radial growth of Pinus sylvestris var. mongolica (PM) and regional vegetation canopy growth along with their climate responses in the semi-arid area of northeastern China, investigating the synchronisation and temperature limitation of the two growths. We also clarified the variation in the synchronisation of radial and canopy growth in a warming climate. The radial growth of PM and canopy growth of regional vegetation increased significantly. Positive correlations between tree-ring width index (RWI) and leaf area index (LAI) during May and June were higher than those during the rest of the months and month-combinations of a year. The synchronisation of the radial growth and the canopy growth significantly increased along increasing gradients of latitude, and significantly decreased along increasing gradients of temperature. Radial and canopy growth were limited in July by minimum temperatures in the northern high-latitude sample sites (cold and arid) of the study area. Warming induced the unsynchronised radial and canopy growth in the semi-arid area. The synchronous change of the two growth types will weak in the study area in the future; the decoupling of tree growth is expected to occur earlier in the cold, dry areas than in the warm, wet areas. Weakened or broken statistical linkages, such as the synchronisation between the radial growth of a tree species and the canopy growth of the regional vegetation, indicate that the decreased effectiveness of a specific tree radial growth as an indicator of regional vegetation growth complicates the up- or down-scale assessment of forest biomass dynamics and its carbon sequestration potential.
Global tree species mapping using remote sensing data is vital for biodiversity monitoring, forest management, and ecological research. However, progress in this field has been constrained by the scarcity of large-scale, labeled datasets. To address this, we introduce GlobalGeoTree, a comprehensive global dataset for tree species classification. GlobalGeoTree comprises 6.3 million geolocated tree occurrences, spanning 275 families, 2,734 genera, and 21,001 species across the hierarchical taxonomic levels. Each sample is paired with Sentinel-2 image time series and 27 auxiliary environmental variables, encompassing bioclimatic, geographic, and soil data. The dataset is partitioned into GlobalGeoTree-6M for model pretraining and curated evaluation subsets, primarily GlobalGeoTree-10kEval for zero-shot and few-shot benchmarking. To demonstrate the utility of the dataset, we introduce a baseline model, GeoTreeCLIP, which leverages paired remote sensing data and taxonomic text labels within a vision-language framework pretrained on GlobalGeoTree-6M. Experimental results show that GeoTreeCLIP achieves substantial improvements in zero- and few-shot classification on GlobalGeoTree-10kEval over existing advanced models. By making the dataset, models, and code publicly available, we aim to establish a benchmark to advance tree species classification and foster innovation in biodiversity research and ecological applications.
Leaf area index (LAI) is a key parameter for modeling ecosystem productivity, climate interactions, and hydrological processes, as well as monitoring vegetation health. While satellite-based estimates provide insights into large-scale vegetation dynamics, ground-based methods, including digital hemispherical photography (DHP), are essential to generate and validate such products and offer a practical alternative for fine-scale assessments. However, it remains unclear if the DHP method enables to robustly track temporal LAI dynamics. Here, we evaluate DHP-derived LAI time series with litter trap (LT)-derived LAI in a temperate deciduous broad-leaved forest. First, by comparing DHP-derived LAI estimates with LT-derived LAI across varying view zenith angles ranging from 10° to 90°, we investigate how well both methods align. Using 15 sample locations, we found the highest average correlation across all locations of DHP- and LT-derived LAI (R2 =0.88) at a view zenith angle of 20°, indicating that litter traps represent a relatively narrow spatial footprint. Uncertainties for individual litter traps attributed to varying site conditions, such as tree stem density or canopy coverage. To overcome these uncertainties, we applied a site specific calibration using the litter traps and a generalized linear mixed model, which significantly increased correlation (R2 =0.97). This study highlights the potential of DHP for tracking spatio-temporal LAI dynamics in decideous forests. Moreover, we demonstrate that integrating DHP and LT data, alongside a mixed-effects model, can enhance the site specific accuracy and applicability of LAI assessments.
[1] We used the Regional Atmospheric Modeling System (RAMS) model to investigate the possible impact of land cover change on the July climate of the coterminous United States over the last 290 years. Vegetation data were estimated using the Ecosystem Demography model. The observed change in land cover leads to a weak warming along the Atlantic coast and a strong cooling of more than 1 K over the Midwest and the Great Plains region. The precipitation signal is weaker and shows some reduction in the Midwest because of changes in the patterns of large-scale moisture advection.
Measurements of atmospheric trace gases provide evidence that fire emissions increased during the 1997/1998 El Niño event and these emissions contributed substantially to global CO2, CO, CH4, and δ13CO2 anomalies. Interpretation and effective use of these atmospheric observations to assess changes in the global carbon cycle requires an understanding of the amount of biomass consumed during fires, the molar ratios of emitted trace gases, and the carbon isotope ratio of emissions. Here we used satellite data of burned area, a map of C4 canopy cover, and a global biogeochemical model to quantitatively estimate contributions of C3 and C4 vegetation to fire emissions during 1997–2001. We found that although C4 grasses contributed to 31% of global mean emissions over this period, they accounted for only 24% of the interannual emissions anomalies. Much of the drought and increase in fire emissions during the 1997/1998 El Niño occurred in tropical regions dominated by C3 vegetation. As a result, the δ13CO2 of the global fire emissions anomaly was depleted (−23.9‰), and explained approximately 27% of the observed atmospheric decrease in δ13CO2 between mid-1997 and the end of 1998 (and 61% of the observed variance in δ13CO2 during 1997–2001). Using fire emissions that were optimized in an atmospheric CO inversion, fires explained approximately 57% of the observed atmospheric δ13CO2 decrease between mid-1997 and the end of 1998 (and 72% of the variance in δ13CO2 during 1997–2001). The severe drought in tropical forests during the 1997/1998 El Niño appeared to allow humans to ignite fires in forested areas that were normally too moist to burn. Adjacent C4 grasses (in woodlands and moist savannas) also burned, but emissions were limited, in part, by aboveground biomass levels that were 2 orders of magnitude smaller than C3 biomass levels. Reduced fuel availability in some C4 ecosystems may have led to a negative feedback on emissions.
Metabolism and phenology of Amazon rainforests significantly influence global dynamics of climate, carbon and water, but remain poorly understood. We analyzed Amazon vegetation phenology at multiple scales with Moderate Resolution Imaging Spectroradiometer (MODIS) satellite measurements from 2000 to 2005. MODIS Enhanced Vegetation Index (EVI, an index of canopy photosynthetic capacity) increased by 25% with sunlight during the dry season across Amazon forests, opposite to ecosystem model predictions that water limitation should cause dry season declines in forest canopy photosynthesis. In contrast to intact forests, areas converted to pasture showed dry-season declines in EVI-derived photosynthetic capacity, presumably because removal of deep-rooted forest trees reduced access to deep soil water. Local canopy photosynthesis measured from eddy flux towers in both a rainforest and forest conversion site confirm our interpretation of satellite data, and suggest that basin-wide carbon fluxes can be constrained by integrating remote sensing and local flux measurements.
Albedo derived from MODIS observations is found to be very stable during November 2000-January 2001. We analyze shortwave albedo under snow and snow-free conditions by IGBP land cover types. Snow changes the spectral property of the surface reflectivity and causes high heterogeneity in the surface albedo between and within land types. The mean black sky (or direct beam) albedo at local solar noon for snow-covered forests is less than 0.30 in the shortwave (0.3-5.0 mum), but it reaches 0.57 for snow-covered grassland and barren. Although we are unable to further separate within-class albedos with fractional tree cover, we find that the normalized difference snow index (NDSI) is highly correlated with surface albedo and hence can be taken as a measure of snow, soil and canopy fraction.
Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 × 107 square kilometres and act as a substantial carbon sink (0.6-0.7 petagrams of carbon per year). Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity, the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide, increasing temperatures, changes in management practices and nitrogen deposition are difficult to disentangle, despite an extensive network of measurement stations. The relevance of this measurement effort has also been questioned, because spot measurements fail to take into account the role of disturbances, either natural (fire, pests, windstorms) or anthropogenic (forest harvesting). Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration. After the confounding effects of disturbance have been factored out, however, forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition, largely the result of anthropogenic activities. The effect is always positive over the range of nitrogen deposition covered by currently available data sets, casting doubts on the risk of widespread ecosystem nitrogen saturation under natural conditions. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly (through forest management) or indirectly (through nitrogen deposition).
1] Climate-carbon cycle model CLIMBER2-LPJ is run with consistent fields of future fossil fuel CO 2 emissions and geographically explicit land cover changes for four Special Report on Emissions Scenarios (SRES) scenarios, A1B, A2, B1, and B2. By 2100, increases in global mean temperatures range between 1.7°C (B1) and 2.7°C (A2) relative to the present day. Biogeochemical warming associated with future tropical land conversion is larger than its corresponding biogeophysical cooling effect in A2, and amplifies biogeophysical warming associated with Northern Hemisphere land abandonment in B1. In 2100, simulated atmospheric CO 2 ranged from 592 ppm (B1) to 957 ppm (A2). Future CO 2 concentrations simulated with the model are higher than previously reported for the same SRES emission scenarios, indicating the effect of future CO 2 emission scenarios and land cover changes may hitherto be underestimated. The maximum contribution of land cover changes to future atmospheric CO 2 among the four SRES scenarios represents a modest 127 ppm, or 22% in relative terms, with the remainder attributed to fossil fuel CO 2 emissions.
Six Earth system models of intermediate complexity that are able to simulate interaction between atmosphere, ocean, and land
surface, were forced with a scenario of land cover changes during the last millennium. In response to historical deforestation
of about 18millionsqkm, the models simulate a decrease in global mean annual temperature in the range of 0.13–0.25°C. The
rate of this cooling accelerated during the 19th century, reached a maximum in the first half of the 20th century, and declined
at the end of the 20th century. This trend is explained by temporal and spatial dynamics of land cover changes, as the effect
of deforestation on temperature is less pronounced for tropical than for temperate regions, and reforestation in the northern
temperate areas during the second part of the 20th century partly offset the cooling trend. In most of the models, land cover
changes lead to a decline in annual land evapotranspiration, while seasonal changes are rather equivocal because of spatial
shifts in convergence zones. In the future, reforestation might be chosen as an option for the enhancement of terrestrial
carbon sequestration. Our study indicates that biogeophysical mechanisms need to be accounted for in the assessment of land
management options for climate change mitigation.
This study explores natural and anthropogenic influences on the climate system, with an emphasis on the biogeophysical and biogeochemical effects of historical land cover change. The biogeophysical effect of land cover change is first subjected to a detailed sensitivity analysis in the context of the UVic Earth System Climate Model, a global climate model of intermediate complexity. Results show a global cooling in the range of –0.06 to –0.22C, though this effect is not found to be detectable in observed temperature trends. We then include the effects of natural forcings (volcanic aerosols, solar insolation variability and orbital changes) and other anthropogenic forcings (greenhouse gases and sulfate aerosols). Transient model runs from the year 1700 to 2000 are presented for each forcing individually as well as for combinations of forcings. We find that the UVic Model reproduces well the global temperature data when all forcings are included. These transient experiments are repeated using a dynamic vegetation model coupled interactively to the UVic Model. We find that dynamic vegetation acts as a positive feedback in the climate system for both the all-forcings and land cover change only model runs. Finally, the biogeochemical effect of land cover change is explored using a dynamically coupled inorganic ocean and terrestrial carbon cycle model. The carbon emissions from land cover change are found to enhance global temperatures by an amount that exceeds the biogeophysical cooling. The net effect of historical land cover change over this period is to increase global temperature by 0.15C.
A full global atmosphere-ocean-land vegetation model is used to examine the coupled climate/vegetation changes in the extratropics
between modern and mid-Holocene (6,000year BP) times and to assess the feedback of vegetation cover changes on the climate
response. The model produces a relatively realistic natural vegetation cover and a climate sensitivity comparable to that
realized in previous studies. The simulated mid-Holocene climate led to an expansion of boreal forest cover into polar tundra
areas (mainly due to increased summer/fall warmth) and an expansion of middle latitude grass cover (due to a combination of
enhanced temperature seasonality with cold winters and interior drying of the continents). The simulated poleward expansion
of boreal forest and middle latitude expansion of grass cover are consistent with previous modeling studies. The feedback
effect of expanding boreal forest in polar latitudes induced a significant spring warming and reduced snow cover that partially
countered the response produced by the orbitally induced changes in radiative forcing. The expansion of grass cover in middle
latitudes worked to reinforce the orbital forcing by contributing a spring cooling, enhanced snow cover, and a delayed soil
water input by snow melt. Locally, summer rains tended to increase (decrease) in areas with greatest tree cover increases
(decreases); however, for the broad-scale polar and middle latitude domains the climate responses produced by the changes
in vegetation are relatively much smaller in summer/fall than found in previous studies. This study highlights the need to
develop a more comprehensive strategy for investigating vegetation feedbacks.
The first results of the UVic Earth System Model coupled to a land surface scheme and a dynamic global vegetation model are presented in this study. In the first part the present day climate simulation is discussed and compared to observations. We then compare a simulation of an ice age inception (forced with 116kaBP orbital parameters and an atmospheric CO2 concentration of 240ppm) with a preindustrial run (present day orbital parameters, atmospheric [CO2] = 280ppm). Emphasis is placed on the vegetations response to the combined changes in solar radiation and atmospheric CO2 level. A southward shift of the northern treeline as well as a global decrease in vegetation carbon is observed in the ice age inception run. In tropical regions, up to 88% of broadleaf trees are replaced by shrubs and C4 grasses. These changes in vegetation cover have a remarkable effect on the global climate: land related feedbacks double the atmospheric cooling during the ice age inception as well as the reduction of the meridional overturning in the North Atlantic. The introduction of vegetation related feedbacks also increases the surface area with perennial snow significantly.
The participation of different vegetation types within the physical climate system is investigated using a coupled atmosphere-biosphere model, CCM3-IBIS. We analyze the effects that six different vegetation biomes (tropical, boreal, and temperate forests, savanna, grassland and steppe, and shrubland/tundra) have on the climate through their role in modulating the biophysical exchanges of energy, water, and momentum between the land-surface and the atmosphere. Using CCM3-IBIS we completely remove the vegetation cover of a particular biome and compare it to a control simulation where the biome is present, thereby isolating the climatic effects of each biome. Results from the tropical and boreal forest removal simulations are in agreement with previous studies while the other simulations provide new evidence as to their contribution in forcing the climate. Removal of the temperate forest vegetation exhibits behavior characteristic of both the tropical and boreal simulations with cooling during winter and spring due to an increase in the surface albedo and warming during the summer caused by a reduction in latent cooling. Removal of the savanna vegetation exhibits behavior much like the tropical forest simulation while removal of the grassland and steppe vegetation has the largest effect over the central United States with warming and drying of the atmosphere in summer. The largest climatic effect of shrubland and tundra vegetation removal occurs in DJF in Australia and central Siberia and is due to reduced latent cooling and enhanced cold air advection, respectively. Our results show that removal of the boreal forest yields the largest temperature signal globally when either including or excluding the areas of forest removal. Globally, precipitation is most affected by removal of the savanna vegetation when including the areas of vegetation removal, while removal of the tropical forest most influences the global precipitation excluding the areas of vegetation removal.
This study examines the impact of historical land-cover change on North American surface climate, focusing on the robustness of the climate signal with respect to representation of sub-grid heterogeneity and land biogeophysics within a climate model. We performed four paired climate simulations with the Community Atmosphere Model using two contrasting land models and two different representations of land-cover change. One representation used a biome classification without subgrid-scale heterogeneity while the other used high-resolution satellite data to prescribe multiple vegetation types within a grid cell. Present-day and natural vegetation datasets were created for both representations. All four sets of climate simulations showed that present-day vegetation has cooled the summer climate in regions of North America compared to natural vegetation. The simulated magnitude and spatial extent of summer cooling due to land-cover change was reduced when the biome-derived land-cover change datasets were replaced by the satellite-derived datasets. The diminished cooling is partly due to reduced intensity of agriculture in the satellite-derived datasets. Comparison of the two land-surface models showed that the use of a comparatively warmer and drier land model in conjunction with satellite-derived datasets further reduced the simulated magnitude of summer cooling. These results suggest that the cooling signal associated with North American land-cover change is robust but the magnitude and therefore detection of the signal depends on the realism of the datasets used to represent land-cover change and the parametrisation of land biogeophysics.
In the southeastern United States (SE), the conversion of abandoned agricultural land to forests is the dominant feature of land-cover change. However, few attempts have been made to quantify the impact of such conversion on surface temperature. Here, this issue is explored experimentally and analytically in three adjacent ecosystems (a grass-covered old-field, OF, a planted pine forest, PP, and a hardwood forest, HW) representing a successional chronosequence in the SE. The results showed that changes in albedo alone can warm the surface by 0.9°C for the OF-to-PP conversion, and 0.7°C for the OF-to-HW conversion on annual time scales. However, changes in eco-physiological and aerodynamic attributes alone can cool the surface by 2.9 and 2.1°C, respectively. Both model and measurements consistently suggest a stronger over-all surface cooling for the OF-to-PP conversion, and the reason is attributed to leaf area variations and its impacts on boundary layer conductance.
Pioneering work in the last century has resulted in a widely accepted
paradigm that primary production is strongly positively related to
temperature and water availability such that the northern hemispheric
forest carbon sink may increase under conditions of global warming.
However, the terrestrial carbon sink at the ecosystem level (i.e. net
ecosystem productivity, NEP) depends on the net balance between gross
primary productivity (GPP) and ecosystem respiration (TER). Through an
analysis of European eddy covariance flux data sets, we find that the
common climate relationships for primary production do not hold for NEP.
This is explained by the fact that decreases in GPP are largely
compensated by parallel decreases in TER when climatic factors become
more limiting. Moreover, we found overall that water availability was a
significant modulator of NEP, while the multivariate effect of mean
annual temperature is small and not significant. These results indicate
that climate- and particularly temperature-based projections of net
carbon balance may be misleading. Future research should focus on
interactions between the water and carbon cycles and the effects of
disturbances on the carbon balance of terrestrial ecosystems.
Coupled climate-carbon cycle models suggest that Amazon forests are vulnerable to both long- and short-term droughts, but satellite observations showed a large-scale photosynthetic green-up in intact evergreen forests of the Amazon in response to a short, intense drought in 2005. These findings suggest that Amazon forests, although threatened by human-caused deforestation and fire and possibly by more severe long-term droughts, may be more resilient to climate changes than ecosystem models assume.
Summary A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO 2 is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO 2 was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO 2 contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO 2 and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.
Comparative measurements of radiation flux components and turbulent fluxes of energy and CO2 are made at two sites in South West Amazonia: one in a tropical forest reserve and one in a pasture. The data were collected from February 1999 to September 2002, as part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). During the dry seasons, although precipitation and specific humidity are greatly reduced, the soil moisture storage profiles down to 3.4 m indicate that the forest vegetation continues to withdraw water from deep layers in the soil. For this reason, seasonal changes observed in the energy partition and CO2 fluxes in the forest are small, compared to the large reductions in evaporation and photosynthesis observed in the pasture. For the radiation balance, the reflected short wave radiation increases by about 55% when changing from forest to pasture. Combined with an increase of 4.7% in long wave radiation loss, this causes an average reduction of 13.3% in net radiation in the pasture, compared to the forest. In the wet season, the evaporative fraction (lambdaE/R-n) at the pasture is 17% lower than at the forest. This difference increases to 24% during the dry season. Daytime CO2 fluxes are 20-28% lower (in absolute values) in the pasture compared to the forest. The night-time respiration in the pasture is also reduced compared to the forest, with averages 44% and 57% lower in the wet and dry seasons, respectively. As the reduction in the nocturnal respiration is larger than the reduction in the daytime uptake, the combined effect is a 19-67% higher daily uptake of CO2 in the pasture, compared to the forest. This high uptake of CO2 in the pasture site is not surprising, since the growth of the vegetation is constantly renewed, as the cattle remove the biomass. Pages: 5-26
Heavy smoke from forest fires in the Amazon was observed to reduce cloud droplet size and so delay the onset of precipitation
from 1.5 kilometers above cloud base in pristine clouds to more than 5 kilometers in polluted clouds and more than 7 kilometers
in pyro-clouds. Suppression of low-level rainout and aerosol washout allows transport of water and smoke to upper levels,
where the clouds appear “smoking” as they detrain much of the pollution. Elevating the onset of precipitation allows invigoration
of the updrafts, causing intense thunderstorms, large hail, and greater likelihood for overshooting cloud tops into the stratosphere.
There, detrained pollutants and water vapor would have profound radiative impacts on the climate system. The invigorated storms
release the latent heat higher in the atmosphere. This should substantially affect the regional and global circulation systems.
Together, these processes affect the water cycle, the pollution burden of the atmosphere, and the dynamics of atmospheric
circulation.
Volcanic aerosols from the 1991 Mount Pinatubo eruption greatly increased diffuse radiation worldwide for the following 2 years. We estimated that this increase in diffuse radiation alone enhanced noontime photosynthesis of a deciduous forest by 23% in 1992 and 8% in 1993 under cloudless conditions. This finding indicates that the aerosol-induced increase in diffuse radiation by the volcano enhanced the terrestrial carbon sink and contributed to the temporary decline in the growth rate of atmospheric carbon dioxide after the eruption.
Land use has generally been considered a local environmental issue, but it is becoming a force of global importance. Worldwide
changes to forests, farmlands, waterways, and air are being driven by the need to provide food, fiber, water, and shelter
to more than six billion people. Global croplands, pastures, plantations, and urban areas have expanded in recent decades,
accompanied by large increases in energy, water, and fertilizer consumption, along with considerable losses of biodiversity.
Such changes in land use have enabled humans to appropriate an increasing share of the planet's resources, but they also potentially
undermine the capacity of ecosystems to sustain food production, maintain freshwater and forest resources, regulate climate
and air quality, and ameliorate infectious diseases. We face the challenge of managing trade-offs between immediate human
needs and maintaining the capacity of the biosphere to provide goods and services in the long term.
Climate change is expected to influence the capacities of the land and oceans to act as repositories for anthropogenic CO2 and hence provide a feedback to climate change. A series of experiments with the National Center for Atmospheric Research–Climate System Model 1 coupled carbon–climate model shows that carbon sink strengths vary with the rate of fossil fuel emissions, so that carbon storage capacities of the land and oceans decrease and climate warming accelerates with faster CO2 emissions. Furthermore, there is a positive feedback between the carbon and climate systems, so that climate warming acts to increase the airborne fraction of anthropogenic CO2 and amplify the climate change itself. Globally, the amplification is small at the end of the 21st century in this model because of its low transient climate response and the near-cancellation between large regional changes in the hydrologic and ecosystem responses. Analysis of our results in the context of comparable models suggests that destabilization of the tropical land sink is qualitatively robust, although its degree is uncertain.
• carbon dioxide
• climate change
• land carbon sink
• ocean carbon sink
Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr(-1)) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.
Climate change predictions derived from coupled carbon-climate models are highly dependent on assumptions about feedbacks between the biosphere and atmosphere. One critical feedback occurs if C uptake by the biosphere increases in response to the fossil-fuel driven increase in atmospheric [CO(2)] ("CO(2) fertilization"), thereby slowing the rate of increase in atmospheric [CO(2)]. Carbon exchanges between the terrestrial biosphere and atmosphere are often first represented in models as net primary productivity (NPP). However, the contribution of CO(2) fertilization to the future global C cycle has been uncertain, especially in forest ecosystems that dominate global NPP, and models that include a feedback between terrestrial biosphere metabolism and atmospheric [CO(2)] are poorly constrained by experimental evidence. We analyzed the response of NPP to elevated CO(2) ( approximately 550 ppm) in four free-air CO(2) enrichment experiments in forest stands. We show that the response of forest NPP to elevated [CO(2)] is highly conserved across a broad range of productivity, with a stimulation at the median of 23 +/- 2%. At low leaf area indices, a large portion of the response was attributable to increased light absorption, but as leaf area indices increased, the response to elevated [CO(2)] was wholly caused by increased light-use efficiency. The surprising consistency of response across diverse sites provides a benchmark to evaluate predictions of ecosystem and global models and allows us now to focus on unresolved questions about carbon partitioning and retention, and spatial variation in NPP response caused by availability of other growth limiting resources.
Adding the effects of changes in land cover to the A2 and B1 transient climate simulations described in the Special Report
on Emissions Scenarios (SRES) by the Intergovernmental Panel on Climate Change leads to significantly different regional climates
in 2100 as compared with climates resulting from atmospheric SRES forcings alone. Agricultural expansion in the A2 scenario
results in significant additional warming over the Amazon and cooling of the upper air column and nearby oceans. These and
other influences on the Hadley and monsoon circulations affect extratropical climates. Agricultural expansion in the mid-latitudes
produces cooling and decreases in the mean daily temperature range over many areas. The A2 scenario results in more significant
change, often of opposite sign, than does the B1 scenario.
Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined
field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses
in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by
227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S.
plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations
can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.
We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black
carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase
radiative forcing during the first year (34 ± 31 Watts per square meter of burned area), but to decrease radiative forcing
when averaged over an 80-year fire cycle (–2.3 ± 2.2 Watts per square meter) because multidecadal increases in surface albedo
had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate
climate warming.
The prevention of deforestation and promotion of afforestation have often been cited as strategies to slow global warming. Deforestation releases CO2 to the atmosphere, which exerts a warming influence on Earth's climate. However, biophysical effects of deforestation, which include changes in land surface albedo, evapotranspiration, and cloud cover also affect climate. Here we present results from several large-scale deforestation experiments performed with a three-dimensional coupled global carbon-cycle and climate model. These simulations were performed by using a fully three-dimensional model representing physical and biogeochemical interactions among land, atmosphere, and ocean. We find that global-scale deforestation has a net cooling influence on Earth's climate, because the warming carbon-cycle effects of deforestation are overwhelmed by the net cooling associated with changes in albedo and evapotranspiration. Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions. Although these results question the efficacy of mid- and high-latitude afforestation projects for climate mitigation, forests remain environmentally valuable resources for many reasons unrelated to climate.
• afforestation
• albedo change
• climate change
• global warming
• climate policy
Measurements of midday vertical atmospheric CO2 distributions reveal annual-mean vertical CO2 gradients that are inconsistent with atmospheric models that estimate a large transfer of terrestrial carbon from tropical
to northern latitudes. The three models that most closely reproduce the observed annual-mean vertical CO2 gradients estimate weaker northern uptake of –1.5 petagrams of carbon per year (Pg C year–1) and weaker tropical emission of +0.1 Pg C year–1 compared with previous consensus estimates of –2.4 and +1.8 Pg C year–1, respectively. This suggests that northern terrestrial uptake of industrial CO2 emissions plays a smaller role than previously thought and that, after subtracting land-use emissions, tropical ecosystems
may currently be strong sinks for CO2.
The evolution of the Earth's climate over the twenty-first century depends on the rate at which anthropogenic carbon dioxide emissions are removed from the atmosphere by the ocean and land carbon cycles. Coupled climate-carbon cycle models suggest that global warming will act to limit the land-carbon sink, but these first generation models neglected the impacts of changing atmospheric chemistry. Emissions associated with fossil fuel and biomass burning have acted to approximately double the global mean tropospheric ozone concentration, and further increases are expected over the twenty-first century. Tropospheric ozone is known to damage plants, reducing plant primary productivity and crop yields, yet increasing atmospheric carbon dioxide concentrations are thought to stimulate plant primary productivity. Increased carbon dioxide and ozone levels can both lead to stomatal closure, which reduces the uptake of either gas, and in turn limits the damaging effect of ozone and the carbon dioxide fertilization of photosynthesis. Here we estimate the impact of projected changes in ozone levels on the land-carbon sink, using a global land carbon cycle model modified to include the effect of ozone deposition on photosynthesis and to account for interactions between ozone and carbon dioxide through stomatal closure. For a range of sensitivity parameters based on manipulative field experiments, we find a significant suppression of the global land-carbon sink as increases in ozone concentrations affect plant productivity. In consequence, more carbon dioxide accumulates in the atmosphere. We suggest that the resulting indirect radiative forcing by ozone effects on plants could contribute more to global warming than the direct radiative forcing due to tropospheric ozone increases.
We used the eddy covariance technique from July 2000 to July 2001 to measure the fluxes of sensible heat, water vapor, and CO 2 between an old-growth tropical forest in eastern Amazonia and the atmosphere. Precipitation varied seasonally, with a wet season from mid-December 2000 to July 2001 characterized by successive rainy days, wet soil, and, relative to the dry season, cooler temperatures, greater cloudiness, and reduced incoming solar and net radiation. Average evapotranspiration decreased from 3.96 6 0.65 mm/d during the dry season to 3.18 6 0.76 mm/d during the wet season, in parallel with decreasing radiation and decreasing water vapor deficit. The average Bowen ratio was 0.17 6 0.10, indicating that most of the incoming radiation was used for evaporation. The Bowen ratio was relatively low during the early wet season (December-March), as a result of increased evaporative fraction and reduced sensible heat flux. The seasonal decline in Bowen ratio and increase in evaporative fraction coincided with an increase in ecosystem CO 2 assimilation capacity, which we attribute to the growth of new leaves. The evaporative fraction did not decline as the dry season progressed, implying that the forest did not become drought stressed. The roots extracted water throughout the top 250 cm of soil, and water redistribution, possibly by hydraulic lift, partially recharged the shallow soil during dry season nights. The lack of drought stress during the dry season was likely a consequence of deep rooting, and possibly vertical water movement, which allowed the trees to maintain access to soil water year round.
Fluxes of energy and water vapor over boreal forest stands are expected to vary during the growing season due to temporal variations in solar energy, soil and air temperature, soil moisture, photosynthetic capacity, and leaf area. To investigate this hypothesis, we measured fluxes of energy balance components (solar, latent and sensible heat, and soil and canopy heat storage) over and under a boreal jack pine forest in central Canada during the 1994 growing season. Temporal trends of daily-integrated energy fluxes were significant during a 117 day period between spring and autumn. Mean fluxes of net radiation and latent heat peaked near the summer solstice. By the autumnal equinox their magnitudes were half of their peak values. On a day-to-day basis the presence or absence of clouds modulated solar energy fluxes, while evaporation rates were dependent on whether the canopy was dry or wet. When the canopy was dry, daily evaporation was generally less than 2.5mmd-1. This amount was less than one-half the rate of equilibrium evaporation and was low compared to evaporation from vegetation in temperate zones. When the canopy was wet, daily evaporation approached 3mmd-1 and exceeded predicted rates of equilibrium evaporation. Evaporation from the dry forest was weakly coupled to available energy and was restricted by the canopy AEs low-surface conductance. Biotic factors limiting the forest AEs surface conductance include the forest AEs low-leaf area index and partial stomatal closure. Abiotic and physiological factors restricting stomatal opening included a scarce supply of soil moisture, limiting vapor pressure deficits and the low photosynthetic capacity of the needles. The fluxes of solar energy and latent and sensible heat at the floor of the forest were a significant portion of energy exchange between the forest and the atmosphere. Typically, 20 to 40% of the total energy exchange by the jack pine stand originated at the understory. Since a substantial amount of energy occurs under the forest, two-layer, not a big-leaf AE, evaporation models are recommended as a tool for estimating water vapor fluxes from this open forest stand.
We examined the response of terrestrial carbon fluxes to climate variability induced by the El Niño-Southern Oscillation (ENSO). We estimated global net primary production (NPP) from 1982 to 1999 using a light use efficiency model driven by satellite-derived canopy parameters from the Advanced Very High Resolution Radiometer and climate data from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project. We estimated a summed heterotrophic respiration and fire carbon flux as the residual between NPP and the terrestrial net carbon flux inferred from an atmospheric inversion model, excluding the impacts of land use change. We propose that for global applications this approach may be more robust than traditional, biophysically based approaches of simulating heterotrophic respiration. NPP interannual variability was significantly related to ENSO, particularly at lower latitudes (22.5°N-22.5°S) but was weakly related to global temperature. Global heterotrophic respiration and fire carbon fluxes were strongly correlated with global temperature (7.9 pgC/°C). Our results confirm the dependence of global heterotrophic respiration and fire carbon fluxes on interannual temperature variability and strongly suggest that ENSO-mediated NPP variability influences the atmospheric CO2 growth rate.
This book introduces an interdisciplinary framework to understand the interaction between terrestrial ecosystems and climate change. It reviews basic meteorological, hydrological and ecological concepts to examine the physical, chemical and biological processes by which terrestrial ecosystems affect and are affected by climate. The textbook is written for advanced undergraduate and graduate students studying ecology, environmental science, atmospheric science and geography. The central argument is that terrestrial ecosystems become important determinants of climate through their cycling of energy, water, chemical elements and trace gases. This coupling between climate and vegetation is explored at spatial scales from plant cells to global vegetation geography and at timescales of near instantaneous to millennia. The text also considers how human alterations to land become important for climate change. This restructured edition, with updated science and references, chapter summaries and review questions, and over 400 illustrations, including many in colour, serves as an essential student guide.
The boreal forest, one of the world's larger biomes, is distinct from other biomes because it experiences a short growing season and extremely cold winter temperatures. Despite its size and impact on the earth's climate system, measurements of mass and energy exchange have been rare until the past five years. This paper overviews results of recent and comprehensive field studies conducted in Canada, Siberia and Scandinavia on energy exchanges between boreal forests and the atmosphere.
How the boreal biosphere and atmosphere interact to affect the interception of solar energy and how solar energy is used to evaporate water and heat the air and soil is examined in detail. Specifically, we analyse the magnitudes, temporal and spatial patterns and controls of solar energy, moisture and sensible heat fluxes across the land–atmosphere interface. We interpret and synthesize field data with the aid of a soil–vegetation–atmosphere transfer model, which considers the coupling of the energy and carbon fluxes and nutrient status.
Low precipitation and low temperatures limit growth of many boreal forests. These factors restrict photosynthetic capacity and lower root hydraulic conductivity and stomatal conductance of the inhabitant forests. In such circumstances, these factors interact to form a canopy that has a low leaf area index and exerts a significant resistance to evaporation. Conifer forests, growing on upland soils, for example, evaporate at rates between 25 and 75% of equilibrium evaporation and lose less than 2.5 mm day−1 of water. The open nature of many boreal conifer forest stands causes a disproportionate amount of energy exchange to occur at the soil surface. The climatic and physiological factors that yield relatively low rates of evaporation over conifer stands also cause high rates of sensible heat exchange and the diurnal development of deep planetary boundary layers. In contrast, evaporation from broad-leaved aspen stands and fen/wetlands approach equilibrium evaporation rates and lose up to 6 mm day−1.
We assess the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO2 emissions, land cover) forcings on the global climate system over the last 150 years using an earth system model of intermediate complexity, CLIMBER-2. We apply several datasets of historical land-use reconstructions: the cropland dataset by Ramankutty & Foley (1999) (R&F), the HYDE land cover dataset of Klein Goldewijk (2001), and the land-use emissions data from Houghton & Hackler (2002). Comparison between the simulated and observed temporal evolution of atmospheric CO2 and δ13CO2 are used to evaluate these datasets. To check model uncertainty, CLIMBER-2 was coupled to the more complex Lund–Potsdam–Jena (LPJ) dynamic global vegetation model.
In simulation with R&F dataset, biogeophysical mechanisms due to land cover changes tend to decrease global air temperature by 0.26°C, while biogeochemical mechanisms act to warm the climate by 0.18°C. The net effect on climate is negligible on a global scale, but pronounced over the land in the temperate and high northern latitudes where a cooling due to an increase in land surface albedo offsets the warming due to land-use CO2 emissions.
Land cover changes led to estimated increases in atmospheric CO2 of between 22 and 43 ppmv. Over the entire period 1800–2000, simulated δ13CO2 with HYDE compares most favourably with ice core during 1850–1950 and Cape Grim data, indicating preference of earlier land clearance in HYDE over R&F. In relative terms, land cover forcing corresponds to 25–49% of the observed growth in atmospheric CO2. This contribution declined from 36–60% during 1850–1960 to 4–35% during 1960–2000. CLIMBER-2-LPJ simulates the land cover contribution to atmospheric CO2 growth to decrease from 68% during 1900–1960 to 12% in the 1980s. Overall, our simulations show a decline in the relative role of land cover changes for atmospheric CO2 increase during the last 150 years.
A combination of satellite imagery, meteorological station data, and the NCEP/NCAR reanalysis has been used to explore the spatial and temporal evolution of the 2003 heat wave in France, with focus on understanding the impacts and feedbacks at the land surface. Vegetation was severely affected across the study area, especially in a swath across central France that corresponds to the Western European Broadleaf (WEB) Forests ecological zone. The remotely sensed surface temperature anomaly was also greatest in this zone, peaking at +15.4 °C in August. On a finer spatial scale, both the vegetation and surface temperature anomalies were greater for crops and pastures than for forested lands. The heat wave was also associated with an anomalous surface forcing of air temperature. Relative to other years in record, satellite-derived estimates of surface-sensible heat flux indicate an enhancement of 48–61% (24.0–30.5 W m−2) in WEB during the August heat wave maximum. Longwave radiative heating of the planetary boundary layer (PBL) was enhanced by 10.5 W m−2 in WEB for the same period. The magnitude and spatial structure of this local heating is consistent with models of the late twenty-first century climate in France, which predict a transitional climate zone that will become increasingly affected by summertime drought. Models of future climate also suggest that a soil-moisture feedback on the surface energy balance might exacerbate summertime drought, and these proposed feedback mechanisms were tested using satellite-derived heat budgets. Copyright © 2006 Royal Meteorological Society.
Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.
Supposed connections between forests and climate are long established in Western tradition and were the subject of speculation in the New World even from the time of Christopher Columbus. The luxuriant forest growth and unusual climate of America early invited conjecture on the climatic effects of the forests and the consequences of their removal. Pioneer settlers in America thought that forest clearing was producing a warming trend and affecting the climate in other ways~ By the nineteenth century there was wide, but not entirely unanimous, belief that deforestation had caused significant climate changes, especially higher temperatures and lower precipitation. It was also believed that tree planting might increase precipitation in the semi-arid West. Later in the nineteenth century, mainly as a result of increasing availability of climatic data, the possibility of a positive or negative macroseale climatic influence for forests was largely dismissed. Modern scientists now attribute an important microscale climatic influence to forests and axe reconsidering the macroscale effects, especially as related to atmospheric carbon dioxide and albedo changes.
Study of the effect of current climate changes on vegetation growth, and their spatial patterns improves our understanding of the interactions between terrestrial ecosystems and climatic systems. This paper explores the spatial patterns of vegetation growth responding to climate variability over Northern Hemisphere (>25°N) from 1980 to 2000 using a mechanistic terrestrial carbon model. The results indicate that changes in climate and atmospheric CO2 likely function as dominant controllers for the greening trend during the study period. At the continental scale, atmospheric CO2, temperature, and precipitation account for 49%, 31%, and 13% of the increase in growing season LAI, respectively, but their relative role is not constant across the study area. The increase in vegetation activity in most of Siberia is associated with warming, while that in central North America is primarily explained by the precipitation change. The model simulation also suggests that the regression slope of LAI to temperatur
A large carbon sink in northern land surfaces inferred from global carbon cycle inversion models led to concerns during Kyoto Protocol negotiations that countries might be able to avoid efforts to reduce fossil fuel emissions by claiming large sinks in their managed forests. The greenhouse gas balance of Canada's managed forest is strongly affected by naturally occurring fire with high interannual variability in the area burned and by cyclical insect outbreaks. Taking these stochastic future disturbances into account, we used the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) to project that the managed forests of Canada could be a source of between 30 and 245 Mt CO2e yr−1 during the first Kyoto Protocol commitment period (2008–2012). The recent transition from sink to source is the result of large insect outbreaks. The wide range in the predicted greenhouse gas balance (215 Mt CO2e yr−1) is equivalent to nearly 30% of Canada's emissions in 2005. The increasing impact o
The prediction of evaporation from Mediterranean woodland ecosystems is complicated by an array of climate, soil and plant factors. To provide a mechanistic and process-oriented understanding, we evaluate theoretical and experimental information on water loss of Mediterranean oaks at three scales, the leaf, tree and woodland. We use this knowledge to address: what limits evaporation from Mediterranean oak woodlands – the supply of moisture in the soil, physiological control by plants or the demand by the atmosphere?The Mediterranean climate is highly seasonal with wet winters and hot, dry summers. Consequently, available sunlight is in surplus, causing potential evaporation to far exceed available rainfall on an annual basis. Because the amount of precipitation to support woody plants is marginal, Mediterranean oaks must meet their limited water supply by a variety of means. They do so by: (1) constraining the leaf area index of the landscape by establishing a canopy with widely spaced trees; (2) reducing the size of individual leaves; (3) by adopting physiological characteristics that meter the use of water (e.g. regulating stomatal, leaf nitrogen/photosynthetic capacity and/or hydraulic conductance); (4), by tapping deep supplies of water in the soil; (5) and/or by adopting a deciduous life form, which reduces the time interval that the vegetation transpires.
Eleven coupled climate–carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO2 for the 1850–2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5°C.
All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.
While a number of gases are implicated in global warming, carbon dioxide is the most important contributor, and in one sense the entire phenomena can be seen as a human-induced perturbation of the carbon cycle. The Global Carbon Cycle offers a scientific assessment of the state of current knowledge of the carbon cycle by the world's leading scientists sponsored by SCOPE and the Global Carbon Project, and other international partners. It gives an introductory over-view of the carbon cycle, with multidisciplinary contributions covering biological, physical, and social science aspects. Included are 29 chapters covering topics including: an assessment of carbon-climate-human interactions; a portfolio of carbon management options; spatial and temporal distribution of sources and sinks of carbon dioxide; socio-economic driving forces of emissions scenarios. Throughout, contributors emphasize that all parts of the carbon cycle are interrelated, and only by developing a framework that considers the full set of feedbacks will we be able to achieve a thorough understanding and develop effective management strategies. The Global Carbon Cycle edited by Christopher B. Field and Michael R. Raupach is part of the Rapid Assessment Publication series produced by the Scientific Committee on Problems of the Environment (SCOPE), in an effort to quickly disseminate the collective knowledge of the world's leading experts on topics of pressing environmental concern.