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We welcome the attention given to forest and trees by the Report “The global tree restoration potential” (5 July, p. 76), in which J.-F. Bastin et al. study the potential of tree cover to reduce climate change. However, we are concerned by their neglect of the water cycle.

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... Отсутствие адекватного учёта динамики почвенного углерода в ненарушенных лесах и других ненарушенных экосистемах приводит к потенциальной недооценке негативного воздействия на углеродный баланс преобразования экосистемы из ненарушенного состояния в нарушенное, в частности, с нарушением водного режима (Kittler et al., 2017;Sheil et al., 2019;Mayer et al., 2020). Если малонарушенные леса России обеспечивают почвенный сток атмосферного углерода, то превращение выделенного участка ненарушенного леса в нарушенный эксплуатируемый участок с лесными культурами с большей чистой первичной продуктивностью приведёт к увеличению выбросов углерода в атмосферу за счёт замены стабилизирующего воздействия (поглощения углерода естественным лесом) на дестабилизирующее (потерю почвенного углерода нарушенной экосистемой) (Dean et al., 2017). ...
... Влияние леса на климат базируется на множестве физических, биохимических и экологических процессов со сложными обратными связями (рис. 1), причём во всех аспектах биотическая регуляция влаги является ключевым фактором (Sheil et al., 2019). Так, образование облачного покрова тесно связано с атмосферным транспортом влаги, который, в свою очередь, зависит от испарения влаги лесом (Wright et al., 2017;. ...
... Сегодня в мировой климатической повестке можно различить тенденции намечающегося концептуального поворота «от углерода к воде». Хотя накопление углерода в лесных экосистемах по-прежнему рассматривается как основной аспект влияния леса на климат, звучат призывы изучать эту проблему более комплексно в гидрологическом и экологическом контексте (например, Sheil et al., 2019;Anderegg et al., 2020). Смена повестки приведёт к тому, что правила учёта влияния различных стран на климат изменятся, причём российские интересы будут затронуты в первую очередь. ...
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In this work, in the light of the latest scientific data, multiple aspects of the regulatory influence of forest ecosystems on climate are considered from the standpoint of the concept of biotic regulation of the environment: carbon absorption in the biomass of trees and soil, regulation of local temperature regime through the transpiration and reflectivity of forest cover, regulation of continental transport of atmospheric moisture and cloudiness. It is shown that under conditions of increasing climatic destabilization, the value of the climate-regulating function of forests and, in particular, its aspects associated with the water cycle, rapidly increases in comparison with the traditional economic functions of the forest. The Forest Code, as the main document regulating the impact of Russian citizens on the forest, should take into account the dynamically developing situation and assign a special role to climate-regulating forests. Considering that natural forest ecosystems have finite stability and climate-regulating potential, which commercially-scaled timber harvesting and other methods of exploitation can completely destroy, it is proposed to achieve a balance between the economic and climate-regulating functions of forests through their spatial delineation. Economic activity must be carried out intensively in previously developed territories where forests have been perturbed beyond their self-recovery threshold. Intact forests, performing a climate-regulating function, are proposed to be separated into a distinct legal category, subject only to protection and intensive study. It is shown that the advancement of the category of climate-regulating forests in the international climate agenda is vital for the protection of the national interests of Russia.
... The intensification of the hydrological cycle as a result of global climate change will be exacerbated if forests are planted on large scales with the aim of mitigating that climate change itself. At the same time, local drying due to global climate change may be compensated by targeted forestation upwind [29,30]. Using a multi-model average of the RCP4.5 runs of the CMIP5 models we quantify and map how forestation would mitigate drying and enhance wetting towards the end of the 21st century (figure 3). ...
... In general, the projected trends follow a 'wetget-wetter, dry-get-drier' pattern [31]. Given the significant potential precipitation benefits of forestation, targeted forest restoration may significantly contribute to the alleviation of drying trends, which could be considered in the identification of target zones of forest restoration [29], among other considerations including biodiversity and effects on people's livelihoods [14,[32][33][34]. There is spatial overlap between the potential afforestation areas that would mitigate drying (figure 3(a)) and those that would enhance wetting (figure 3(c)), owing to the fact that the 'footprints' or 'evaporationsheds' [28] of evaporation sources tend to be spatially extended and variable (figure 1; [5,35]). ...
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Forest restoration is increasingly applied as a climate change mitigation measure. Apart from sequestering carbon, the large-scale addition of trees on Earth may enhance global precipitation levels. Here we estimate the global precipitation effects of the global forest potential by estimating its effects on evaporation and simulating the downwind precipitation effect of the moisture added to the atmosphere. We find that maximum forestation would on average increase evaporation by 0.6 mm/day and that two-thirds of that additional evaporation would rain out over land, especially during the growing season. Next, by excluding natural grasslands and prioritizing precipitation enhancement above areas that are projected to become drier due to global climate change, we establish where on Earth forest restoration would have the greatest precipitation benefits. Our results thus provide a first step towards forest restoration programs as double climate-change mitigation efforts.
... The same concerns other life-essential resources like freshwater on land that is characterized by a transient store (Table 2). Water cycle is heavily impacted by the presence of natural forests and deteriorates if those are replaced by plantations [35,41]. ...
... Natural ecosystems exert a strong control on local surface temperature, via transpiration on land and control of water transparency in aquatic ecosystems [20,39], as well as via cloud formation [16,41]. The presence of an ocean with its nearly infinite store of atmospheric moisture results in a major thermal climatic instability: the concentration of water vapor, the major greenhouse gas, doubles per every ten degrees of temperature rise, thus increasing the greenhouse effect and further increasing the temperature. ...
There are two contrasting views on life and Earth’s habitability. One view is that the program of environmental regulation by life cannot exist, because it is genetically unstable. A program of “common environmental good” cannot be stabilized by natural selection and would have been disrupted by selfish mutants. The ever-changing Earth’s environment has remained suitable for the ever-adapting life by chance. The second view is that the Earth could not have remained habitable by chance, because the life-compatible environment is physically unstable. Life regulates the environment, but the program of regulation has persisted by chance (for some reason, the disruptive mutants never spread). Neither view forms a quantitative theory of life-environment interaction. Here I discuss the biotic regulation theory, whereby the genetic and environmental stability are mutually guaranteed: the genetic program of environmental regulation by life encodes such an environment where disruptive mutants cannot spread. The key interdisciplinary question is what these environmental properties are. This is not an academic question: once the natural ecosystems are destroyed, the environment will rapidly degrade even if carbon emissions discontinue. Global change mitigation efforts can be misguided if the key role of natural ecosystems in stabilizing a life-favorable environment continues to be neglected.
... If natural forest ecosystems have evolved to stabilize and sustain the continental water cycle, their destruction contributes to destabilization and impoverishment of regional water cycles. This contribution is underestimated (Sheil et al., 2019). Future studies of vegetation cover impacts on atmospheric moisture flows must emphasize the role of natural forests (Zemp et al., 2017a;Sheil, 2018;Makarieva et al., 2020;Leite-Filho et al., 2021;Hua et al., 2022). ...
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The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff, and atmospheric moisture convergence (net import of water vapor to balance runoff). Each of these processes is essential for human and ecosystem well-being. Predicting how the water cycle responds to changes in vegetation cover remains a challenge. Recently, changes in plant transpiration across the Amazon basin were shown to be associated exponentially with changes in rainfall, suggesting that even small declines in transpiration (e.g. from deforestation) would lead to much larger declines in rainfall. Here, constraining these findings by the law of mass conservation, we show that in a sufficiently wet atmosphere, forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import and resulting water yield. Conversely, in a sufficiently dry atmosphere increased transpiration reduces atmospheric moisture convergence and water yield. This previously unrecognized dichotomy explains the otherwise mixed observations of how water yield responds to re-greening, as we illustrate with examples from China's Loess Plateau. Our analysis indicates that any additional moisture recycling due to additional vegetation increases precipitation but decreases local water yield and steady-state runoff. Therefore, in the drier regions/periods and early stages of ecological restoration, the role of vegetation can be confined to moisture recycling, while once a wetter stage is achieved, additional vegetation enhances atmospheric moisture convergence. Evaluating the transition between regimes, and recognizing the potential of vegetation for enhancing moisture convergence, are crucial for characterizing the consequences of deforestation as well as for motivating and guiding ecological restoration.
... One of the limitations of the present study is the short record length, constrained by the available satellite soil moisture data set (January 2010 to December 2018), in particular to understand the dynamics at interannual (ENSO) timescales. Other studies must involve longer data sets to disentangle the linkages between the hydrologic cycle and vegetation activity in the study regions [74][75][76][77]. ...
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We evaluated the coupled dynamics of vegetation dynamics (NDVI) and soil moisture (SMOS) at monthly resolution over different regions of tropical South America and the effects of the Eastern Pacific (EP) and the Central Pacific (CP) El Niño–Southern Oscillation (ENSO) events. We used linear Pearson cross-correlation, wavelet and cross wavelet analysis (CWA) and three nonlinear causality methods: ParrCorr, GPDC and PCMCIplus. Results showed that NDVI peaks when SMOS is transitioning from maximum to minimum monthly values, which confirms the role of SMOS in the hydrological dynamics of the Amazonian greening up during the dry season. Linear correlations showed significant positive values when SMOS leads NDVI by 1–3 months. Wavelet analysis evidenced strong 12- and 64-month frequency bands throughout the entire record length, in particular for SMOS, whereas the CWA analyses indicated that both variables exhibit a strong coherency at a wide range of frequency bands from 2 to 32 months. Linear and nonlinear causality measures also showed that ENSO effects are greater on SMOS. Lagged cross-correlations displayed that western (eastern) regions are more associated with the CP (EP), and that the effects of ENSO manifest as a travelling wave over time, from northwest (earlier) to southeast (later) over tropical South America and the Amazon River basin. The ParrCorr and PCMCIplus methods produced the most coherent results, and allowed us to conclude that: (1) the nonlinear temporal persistence (memory) of soil moisture is stronger than that of NDVI; (2) the existence of two-way nonlinear causalities between NDVI and SMOS; (3) diverse causal links between both variables and the ENSO indices: CP (7/12 with ParrCorr; 6/12 with PCMCIplus), and less with EP (5/12 with ParrCorr; 3/12 with PCMCIplus).
... Climate benefits from massive global re-and afforestation goals (Bastin et al., 2019;Houghton et al., 2015;Houghton and Nassikas, 2018;Chen et al., 2019) will only emerge if such strategies can be adequately linked with rapidly improving knowledge on forest-water interactions Ellison et al., 2017;Creed and van Noordwijk, 2018;Sheil et al., 2019). One of the peculiarities of the original GGW tree-planting idea is its almost blind faith in the view that a wall of trees would be enough to strengthen or reinforce the hydrologic cycle, restrict and even reverse the southward progress of the Sahara and thereby secure landscape resilience (Woodfine and Jauffret, 2009). ...
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Enjoying the potential climate benefits of restoration requires linking key forest-water and land-atmosphere interactions to the existential benefits provided on the ground. We apply a forest-water and land-atmosphere interaction lens to current strategies for improving landscape resilience in the West African Sahel and the concept of the Great Green Wall (GGW). The severe and extensive drought of the 1970's–1990's led many to assess future climate and promote strategies to counter the gradual southward expansion of the Sahara. The idea for the GGW, a wall of trees intended to slow desert encroachment, grew out of this period of tremendous upheaval and human tragedy. Despite partial recovery in the local rainfall regime, we know far too little about whether the GGW strategy can even work. Further, it seems disingenuous to ignore the climatic envelope, which sets the boundaries within which forest-water and land-atmosphere interactions occur. Applying what we call the “forest-water and land-atmosphere interaction lens” to landscape restoration as a tool for achieving improved resilience and human welfare in the Sahel provides meaningful input for re-thinking the GGW strategy. We upgrade current knowledge with the specific biophysical conditions likely to support appropriate forest-water and land atmosphere interactions in the region and further fit such approaches within the context of the climatic envelope. The principal components of an improved strategy include a focus on large scale precipitation recycling all the way from the West African coast on into the Sahel, as well as improved tree, shrub and forest cover in the Sahel proper to promote infiltration, groundwater recharge, rainfall triggering potential and land surface cooling. Agroforestry can further broadly promote landscape resilience in the entire region. Strategies broadly focused on increasing rainfall recycling, water availability and the promotion of landscape resilience appear more likely to steer future efforts in useful directions.
... Ignoring feedbacks with albedo, atmospheric CO 2 2-4 and the water cycle 8 Argued that exploring the effects of albedo was beyond the scope of their study and did not meaningfully comment on the water cycle 9,10 Ignoring fire and herbivory 3 Argued that these are included in the training data as they are from protected areas, although they are not explicitly included in the model 9 ...
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In a time of environmental crisis and ‘fake news’, there are calls for scientists to engage in public debate or advocacy. Some are wary, fearing that revealing subjective views poses a risk to scientific credibility or erodes trust in scholarly publishing. Others are less concerned, seeing it as their duty to society or an opportunity to boost their profile. Ideally, we need better checks and balances that allow scientists to contribute to public discourse without fear of compromising the credibility of their science, while avoiding subjective views influencing the outcomes of peer-reviewed research. For better or worse, scientists have personal views. The question is not whether they should be condoned or condemned, but how they should be managed in the context of scholarly publishing to maximise benefits and minimise negative outcomes. Using the recent contention around global tree ‘restoration’ potential as an example, I propose we score journals and articles based on the Transparency and Openness Promotion (TOP) guidelines and associated criteria. A high TOP score means readers have sufficient access to information to assess the objectivity and credibility of scientific publications and their authors. I show that current practice provides very little access to information, and readers are essentially being asked to have faith in the scholarly publication system. We must do better. Significance: • Science is predicated upon objectivity, yet readers are rarely given enough information to assess the objectivity, and thus integrity, of peer-reviewed research. • To address this issue, a scoring system is proposed, which is based on the principles of transparency and openness. • Improving transparency and openness in scholarly publishing is essential for allowing readers to assess the objectivity of published research and researchers, growing public trust, and allowing researchers to engage in public debates without fear of loss of scientific credibility.
... A wide range of other environmental, social, cultural and political factors not considered in this study could also influence decision-making during different phases of the reforestation process. These include differing rates of soil carbon sequestration across habitat types, as well as planting, post-planting monitoring and the harvesting of propagules, all of which could ultimately affect the climate mitigation potential of reforestation as a nature-based climate solution 22,26,28,29 . Our intent is not to produce precise estimates of the climate mitigation potential of reforestation (other recent studies have done so 5,7,9 ) but rather to illustrate through scenario analysis how this potential can quickly diminish when practical constraints are considered in the Southeast Asian context. ...
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As climate change continues to threaten human and natural systems, the search for cost-effective and practical mitigation solutions is gaining momentum. Reforestation has recently been identified as a promising nature-based climate solution. Yet there are context-dependent biophysical, financial, land-use and operational constraints to reforestation that demand careful consideration. Here, we show that 121 million ha of presently degraded land in Southeast Asia, a region noted for its significant reforestation potential, are biophysically suitable for reforestation. Reforestation of this land would contribute 3.43 ± 1.29 PgCO2e yr⁻¹ to climate mitigation through 2030. However, by taking a combination of on-the-ground financial, land use and operational constraints into account, we find that only a fraction of that mitigation potential may be achievable (0.3–18%). Such constraints are not insurmountable, but they show that careful planning and consideration are needed for effective landscape-scale reforestation.
... These theories indicate that local climates switch from wetter to drier and vice versa with critical losses or gains in tree cover. If sufficient tree cover was established over broad dryland areas it seems that net rainfall would increase, with the wider benefits that that implies (Sheil 2018;Sheil et al. 2019). ...
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The restoration of tree cover influences water availability. Many people—some experts too—believe incorrectly that greater tree cover has an invariably negative impact on local water availability. Where do these beliefs come from? Here we summarise the origin of these misconceptions and illustrate how tree cover can improve water availability. We have recognised the extent of these opportunities only recently, and considerable work remains, but we know enough to dismiss some myths and to highlight major opportunities to improve water security in Africa by restoring degraded landscapes with trees.
... Además, proporcionan bienes y servicios tales como agua limpia y suelos saludables, valorados entre 75 y 100 000 millones de dólares por año, y albergan el 80 % de la biodiversidad terrestre del mundo (iucn, 2020). Absorben aproximadamente 2600 millones de toneladas de CO 2 por año (un tercio del emitido por la quema de combustibles fósiles), y brindan muchos otros beneficios a los humanos y a la naturaleza (Sheil et al., 2019). Alrededor de 1600 millones de personas, la mayoría los más pobres, dependen de los bosques como 63Gar antizar la integridad de los ecosistemas de Colombia medio de vida. ...
... Ces théories indiquent que les climats locaux passent du plus humide au plus sec et vice versa avec des pertes ou des gains critiques de couvert arboré. Si un couvert arboré suffisant était établi sur de vastes zones arides, il semble que les précipitations nettes augmenteraient, avec les avantages plus grands que cela implique (Sheil 2018 ;Sheil et al. 2019). ...
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Les mécanismes par lesquels les arbres influencent la disponibilité de l'eau restent mal compris, mais les deux dernières décennies ont apporté des progrès étonnants. Nous en savons déjà assez pour voir les opportunités majeures d'améliorer la sécurité de l'eau dans les zones arides tropicales grâce au couvert arboré, tout en produisant les nombreux autres avantages que les arbres procurent.
... Ces théories indiquent que les climats locaux passent du plus humide au plus sec et vice versa avec des pertes ou des gains critiques de couvert arboré. Si un couvert arboré suffisant était établi sur de vastes zones arides, il semble que les précipitations nettes augmenteraient, avec les avantages plus grands que cela implique (Sheil 2018 ;Sheil et al. 2019). ...
... Still, restoring previously deforested lands may benefit drought-stressed areas downwind from those lands more than is currently assumed. The advantages and disadvantages of forest restoration are currently heavily debated (e.g., Bastin et al., 2019aBastin et al., , 2019bLewis et al., 2019;Veldman et al., 2019), but the effects on precipitation have been understudied (Sheil et al., 2019). ...
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The Amazon forest enhances precipitation levels regionally as trees take up water from the soil and release it back into the atmosphere through transpiration. Therefore, land-use changes in the Amazon affect precipitation patterns but to what extent remains unclear. Recent studies used hydrological and atmospheric models to estimate the contribution of tree transpiration to precipitation but assumed that precipitation decreases proportionally to the transpired portion of atmospheric moisture. Here, we relaxed this assumption by, first, relating observed hourly precipitation levels to atmospheric column water vapor in a relatively flat study area encompassing a large part of the Amazon. We found that the effect of column water vapor on hourly precipitation was strongly nonlinear, showing a steep increase in precipitation above a column water vapor content of around 60 mm. Next, we used published atmospheric trajectories of moisture from tree transpiration across the whole Amazon to estimate the transpiration component in column water vapor in our study area. Finally, we estimated precipitation reductions for column water vapor levels without this transpired moisture, given the nonlinear relationship we found. Although loss of tree transpiration from the Amazon causes a 13% drop in column water vapor, we found that it could result in a 55%–70% decrease in precipitation annually. Consequences of this nonlinearity might be twofold: although the effects of deforestation may be underestimated, it also implies that forest restoration may be more effective for precipitation enhancement than previously assumed.
... These findings have important implications for food security, as many key grain-basket areas are rain-fed and depend on remotely generated rainfall. FTA has also contributed to the debate of where to plant trees by emphasizing the need to consider the influence that trees exert on local and regional hydrology (Sheil et al. 2019), as well as discerning when and where to rely on natural forest regrowth (i.e., passive approaches) versus tree planting Chazdon et al. 2020b;Lohbeck et al. 2020). ...
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Forest and landscape restoration (FLR) provides a framework for implementing restorative interventions that collectively address major environmental challenges such as soil and land degradation, biodiversity loss, water scarcity, lack of sustainable rural livelihoods, and climate change mitigation and adaptation. Restorative interventions can take many forms, which vary in cost, trajectory and specific economic and social outcomes; likewise, their benefits accrue to various actors and stakeholders. Over the last decade, the CGIAR Program on Forests, Trees and Agroforestry (FTA) has undertaken innovative basic and applied research across different scientific disciplines on the multiple dimensions of FLR for improving policy and practice and facilitating the uptake of new knowledge, tools and approaches — both from the top down and the bottom up. This publication presents key FTA outputs on forest and landscape restoration from 2011 to 2021. Many of them have contributed to informing the implementation of FLR interventions at multiple scales of work. These outputs are presented according to five broad areas of influence: (i) contributions to restoration science; (ii) contributions to global narratives and discourses; (iii) contributions to policy and governance; (iv) focusing on actors on the ground; and (v) contributions to national and international dialogues. The last section discusses ways to move forward.
... The factors controlling SW variability differ with plant type because of their unique characteristics related to hydrology (Bouaziz et al., 2020;Dekker et al., 2007). Shallow-rooted plants can retain more water in soils because of small roots, weak water uptake capacity, high percolation and low evapotranspiration (Markewitz et al., 2010;Wang et al., 2012;Ye et al., 2019), and this can lead to spatially varied SW under different rainfall patterns (Sheil et al., 2019;Zhang et al., 2020b). In contrast, deep-rooted plants decrease SW by intense leaf interception and evaporation above the surface and strong root water uptake below the surface (Markewitz et al., 2010;Wang et al., 2012). ...
Identifying the variability and predominant factors affecting soil water (SW) is essential in regions with thick vadose zones and deep-rooted plants. This information is needed to clarify the balance between water availability and plant water demand. We collected 9263 soil samples from 128 profiles of 7–25 m deep soil under different climates (arid, semiarid and subhumid), soil textures and plant types (shallow or deep roots) in China's Loess Plateau. The factors dominating the horizontal and vertical variability of SW were identified using a multimodel inference approach and stepwise regression analysis. Horizontally, the mean water content and storage increased while the water deficits decreased from the northwest to the southeast. Vertically, mean water content and storage are highest in the relatively stable layer, followed by rapidly changing layers and active layers. Plant age and soil clay content dominate the horizontally varied SW, while plant age and normalized difference vegetation index (NDVI) dominate the vertical variability of SW. However, the dominant factors appeared to differ with climate and plant type. It was determined that for climate, soil clay content and plant age in arid regions, precipitation and plant age in semiarid regions, NDVI and plant age in subhumid regions were important factors. For plants, the dominant factors are NDVI and precipitation under shallow-rooted plants; however, NDVI and plant age were dominant under deep-rooted plants. The dominance of plant age highlighted the impact of vegetation patterns on SW, especially for deep-rooted plants, which should be taken into account when managing water resources and ecosystem rehabilitation in degraded regions.
... If natural forest ecosystems have evolved to stabilize and sustain the continental water cycle, their destruction contributes to destabilization and impoverishment of regional water cycles. This contribution is underestimated (Sheil et al., 2019). ...
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The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff and atmospheric moisture convergence. Each of these fluxes is essential for human and ecosystem well-being. However, predicting how the water cycle responds to changes in vegetation cover, remains a challenge (Lawrence and Vandecar, 2015; Ellison et al., 2017; te Wierik et al., 2021). Recently, rainfall was shown to decrease disproportionally with reduced forest transpiration following deforestation (Baudena et al., 2021). Here, combining these findings with the law of matter conservation, we show that in a sufficiently wet atmosphere forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import. Conversely, in a drier atmosphere increased transpiration reduces atmospheric moisture convergence and runoff. This previously unrecognized dichotomy can explain the seemingly random observations of runoff and soil moisture sometimes increasing and sometimes reducing in response to re-greening (e.g., Zheng et al., 2021). Evaluating the transition between the two regimes is crucial both for characterizing the risk posed by deforestation as well as for motivating and guiding global ecosystem restoration.
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Landscape carbon storage is a key component of climate change mitigation. Tree planting on degraded land has been identified as an effective carbon capture strategy, but it is unclear how various associated restoration treatments influence carbon sequestration. In this study, we measured carbon pools in jack pine (Pinus banksiana Lamb.) stands subject to different restoration treatments within severely damaged upland areas in the metal mining region of Sudbury, Ontario, Canada. Treatments included: i) soil amendment (liming, fertilizing and grass/legume seeding) followed by jack pine planting, ii) jack pine planting alone, iii) soil amendment only, and iv) untreated plots with some natural regeneration as a result of improving air quality in the region. Twenty-four years after the initial treatments, we measured the carbon storage in coarse and fine woody debris, herbs, shrubs, forest floor (LFH), mineral soil, and trees. The carbon pool in planted trees was 1.5 times higher in plots when soil amendments were applied. This increase in the tree carbon pool was the result of greater carbon sequestration per individual jack pine tree rather than changes in tree density or arrival of new species. Similarly, naturally regenerated white birch (Betula papyrifera Marshall) in the amended plots stored 1.7 times more carbon than white birch in the untreated plots. Tree planting proved essential on this landscape with natural tree regeneration rates very low even 50 years after local pollution was massively reduced. However, tree planting surprisingly did not significantly affect total carbon storage in these exposed upland sites. Total ecosystem carbon varied from 21.4 Mg ha-1 to 124.5 Mg ha-1 across all plots (mean of 67.6  4.8 Mg ha-1) but no statistically significant differences were observed among the treatments. Soil organic carbon (SOC) proved to be the largest carbon pool across plots and stored on average 66% of total ecosystem carbon. However, at this early stage the restoration treatments had no influence on SOC pools on this highly degraded landscape, which still appears to be severely affected by ongoing erosion of surface soil and metal contamination. The restoration treatment also did not significantly affect the understory or downed woody debris carbon pools. This study demonstrates that the current restoration treatments used in Sudbury do influence the amount of carbon sequestrated mainly through tree restoration on this industrially degraded landscape, but long-term storage potential is still limited by poor soil conditions.
Technical Report
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Das vorgelegte Förderkonzept beruht darauf, dass auf Grundlage von ausgewählten Indikatoren, tatsächlich existierende ökosystemare Funktionen und Leistungen in Form von (monetären) Prämien gefördert werden können. Folgende Indikatoren wurden als Proxy-Variablen für die Gemeinwohlleistungen der Wälder vorgeschlagen: Kühlungsprämie, Vitalitätsprämie, Biomasseprämie und Strukturvielfaltsprämie. Die benötigten Daten werden durch jährlich überprüfbaren Fernerkundungsdaten erhoben.
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Zusammenfassung Die offenkundigen Schädigungen der von den Extremwitterungen der vergangenen Jahre betroffenen Wälder geben Anlass zu einer Diskussion, die über die Wahl ökonomisch relevanter Baumarten für zukünftige Pflanzungen weit hinausgehen muss. Es bedarf einer ökosystemaren Perspektive und der Einsicht, dass die Vulnerabilität der Wälder gegenüber dem Klimawandel wesentlich durch den Zustand des Gesamtsystems einschließlich aller Organismen wie etwa Pilze und Mikroorganismen sowie den Zustand der ökologischen Prozesse geprägt werden. Klimasystem und Ökosysteme sind überaus komplex und entziehen sich durch dynamisch neu auftretende Wechselwirkungen sowie Rückkopplungen einer verlässlichen Modellierung. Tatsächlich wurden diverse im Rahmen der globalen Erwärmung auftretenden Phänomene erheblich unterschätzt. Es ist kontraproduktiv und gefährlich, sich ein vermeintlich genaues Bild von der Zukunft zu machen und aus ihm Strategien abzuleiten. Sicher scheint nur, dass die globale Erwärmung noch für längere Zeit voranschreiten wird und zwar in einem Ausmaß, mit einer Durchschnittsgeschwindigkeit und in solche Temperaturbereiche hinein, dass die bevorstehende Situation für die heutigen Ökosysteme als völlig neuartig gelten muss. In jedem Falle ist es in den Wäldern besonders relevant, die auftretenden Störungen bestmöglich abpuffern zu können und damit mehr Zeit für Anpassung bzw. Wandlung zu gewinnen. In Ökosystemen bilden sich durch Diversität und Redundanz ‚Sicherheitsnetze‘; zum anderen werden Puffer und Selbstregulation ausgebildet, die die potenzielle Verwundbarkeit reduzieren. Reife und ungestörte agierende Ökosysteme kennzeichnen sich durch eine ausgeprägte Regulation von Standortbedingungen wie Mikroklima und Wasserspeicherung sowie den fortgesetzten Aufbau des eigenen Substrats – Fähigkeiten, die es zu fördern gilt. Aktuell geschieht in Deutschland großflächig das Gegenteil. Forstliche Akteure agieren– auch im Rahmen von staatlich geförderten Maßnahmen - mit Kahlschlägen, der Befahrung und Räumung großer Flächen. Dies geschieht, ohne dass eine angemessene Abschätzung der Folgen und Risiken für Waldökosysteme, die Biodiversität in Deutschland und die gesamte Umwelt durchgeführt worden wäre. Es besteht Anlass zur Befürchtung, dass die Maßnahmen ganze Landschaftsökosysteme, die Biodiversität und den Naturhaushalt nachhaltig beeinträchtigen und damit nicht mit Biodiversitäts-, Wasser- und Bodenschutzgesetzgebung vereinbar sind. Hitze in der Landschaft ist ein zentrales Problem, dem noch zu wenig Beachtung geschenkt wird. Höhere Temperaturen wirken mehrfach schädlich auf Pflanzen. Neben Hitzestress und der Verringerung der Wasserverfügbarkeit durch Austrocknung des Bodens kommt die austrocknende Wirkung heißer Luft hinzu, wobei der Effekt mit steigender Temperatur nichtlinear zunimmt. Wälder und Forsten, landwirtschaftliche Flächen, Wasser, Siedlungen und industriell genutzte Flächen sind nicht voneinander isoliert zu betrachten, zu beplanen sowie so zu nutzen sind, als wären sie voneinander unabhängig. Eine ökosystembasierte Klimawandelanpassungsstrategie müsste eine entsprechende Integration leisten. Es erscheint dringend geboten, Wald und umgebende Landschaft so zu steuern, dass Kühlung und Wasserrückhaltung zur verbesserten Regeneration und Entwicklung von Wäldern beitragen. Es existieren nach wie vor Freiheitsgrade für die Waldentwicklung mit den in naturnahen Ökosystemen vorhandenen Arten. Die aktuellen Nutzungsformen gehören auf den Prüfstand. In naturnahen und vor allem älteren Laubmischwäldern muss ab sofort ein Einschlagsmoratorium verhängt werden. Dies muss gelten, bis klarer wird, wie die Wälder auf die aktuelle Periode von Extremwitterungen reagieren und wie v.a. unterschiedliche Bewirtschaftungsweisen die Waldvulnerabilität erhöhen. Mittelfristig ist ein Maßnahmenpaket zur Förderung der Waldfunktionalität umzusetzen. In den Nadelbaumforsten muss kurzfristig ein totales Verbot des Kahlschlags jeglicher Größe gelten. Für den Umgang mit Flächen, auf denen Kalamitäten aufgetreten sind, sich verstärken oder auftreten werden, müssen dringend für alle Besitzarten verbindliche Behandlungsrichtlinien verabschiedet werden. Die gesamtökonomische Bilanzierung der Waldbewirtschaftung ist auf ein gänzlich neues Fundament zu stellen. Vor allem muss die Verquickung betriebswirtschaftlicher und volkswirtschaftlicher Aspekte offengelegt werden. Versteckte oder mutmaßliche Kosten sowie Subventionen sind genauso zu identifizieren und darzustellen wie alle Quellen von Schad- und Wertschöpfung – einschließlich aller Ökosystemleistungen, die von Wäldern bereitgestellt werden. Benötigt wird eine ganzheitliche Gemeinwohlbilanzierung des Waldes. Eine Art Flächenprämie für die pauschale Förderung von Waldflächen unabhängig von ihrer Beschaffenheit ist kontraproduktiv. Es darf durch Förderung v.a. keine perversen Anreize zur Ökosystemdegradation wie etwa Kahlschläge und Totholzräumung geben. Aktivitäten zur Waldmehrung sowie biodiversitätsfreundliche Entwicklung von Kalamitätsflächen tragen kurzfristig zur Vermeidung von CO2-Emissionen und zur Bewahrung bzw. Entwicklung weiterer regulierender Ökosystemleistungen bei. Es gibt bereits privatwirtschaftliche Initiativen, die sich zum Ziel gesetzt haben, Besitzer*innen entsprechender Flächen den Zugang zu den entsprechenden Märkten zu ermöglichen und transparente Zertifikate auszustellen. Eine ‚Hitzesteuer‘ für Flächen, die überdurchschnittlich stark zur Erwärmung der Landschaft beitragen, könnte einen Anreiz für Maßnahmen bieten, die den Temperatureffekt eindämmen, sowie Einnahmen für die Förderung von Kühlung generieren. Zu besteuernde Flächen beträfen etwa großflächige Gebäude/Dächer, versiegelte Verkehrsflächen oder Tagebaue. Landnutzende könnte von einer entsprechenden Besteuerung ausgenommen werden, aber als Empfänger der Förderung kühlender Maßnahmen in Frage kommen. Vitale Waldökosysteme könnten so Einkommen generieren, und auf Kalamitätsflächen ergäben sich Anreize dafür, auf radikale Flächenbehandlungen zu verzichten.
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Tropical forests modify the conditions they depend on through feedbacks at different spatial scales. These feedbacks shape the hysteresis (history-dependence) of tropical forests, thus controlling their resilience to deforestation and response to climate change. Here, we determine the emergent hysteresis from local-scale tipping points and regional-scale forest-rainfall feedbacks across the tropics under the recent climate and a severe climate-change scenario. By integrating remote sensing, a global hydrological model, and detailed atmospheric moisture tracking simulations, we find that forest-rainfall feedback expands the geographic range of possible forest distributions, especially in the Amazon. The Amazon forest could partially recover from complete deforestation, but may lose that resilience later this century. The Congo forest currently lacks resilience, but is predicted to gain it under climate change, whereas forests in Australasia are resilient under both current and future climates. Our results show how tropical forests shape their own distributions and create the climatic conditions that enable them.
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Destabilization of the water cycle threatens human lives and livelihoods. Meanwhile our understanding of whether and how changes in vegetation cover could trigger abrupt transitions in moisture regimes remains incomplete. This challenge calls for better evidence as well as for the theoretical concepts to describe it. Here we briefly summarise the theoretical questions surrounding the role of vegetation cover in the dynamics of a moist atmosphere. We discuss the previously unrecognized sensitivity of local wind power to condensation rate as revealed by our analysis of the continuity equation for a gas mixture. Using the framework of condensation-induced atmospheric dynamics, we then show that with the temperature contrast between land and ocean increasing up to a critical threshold, ocean-to-land moisture transport reaches a tipping point where it can stop or even reverse. Land-ocean temperature contrasts are affected by both global and regional processes, in particular, by the surface fluxes of sensible and latent heat that are strongly influenced by vegetation. Our results clarify how a disturbance of natural vegetation cover, e.g., by deforestation, can disrupt large-scale atmospheric circulation and moisture transport. In view of the increasing pressure on natural ecosystems, successful strategies of mitigating climate change require taking into account the impact of vegetation on moist atmospheric dynamics. Our analysis provides a theoretical framework to assess this impact. The available data for Eurasia indicate that the observed climatological land-ocean temperature contrasts are close to the threshold. This can explain the increasing fluctuations in the continental water cycle including droughts and floods and signifies a yet greater potential importance for large-scale forest conservation.
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Este trabajo es una versión extendida de un capítulo que hace parte del Vol. No. 3 de las recomendaciones de la Misión Internacional de Sabios 2019.
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The effects of land-use change on river flows have usually been explained by changes within a river basin. However, land–atmosphere feedback such as moisture recycling can link local land-use change to modifications of remote precipitation, with further knock-on effects on distant river flows. Here, we look at river flow changes caused by both land-use change and water use within the basin, as well as modifications of imported and exported atmospheric moisture. We show that in some of the world’s largest basins, precipitation was influenced more strongly by land-use change occurring outside than inside the basin. Moreover, river flows in several non-transboundary basins were considerably regulated by land-use changes in foreign countries. We conclude that regional patterns of land-use change and moisture recycling are important to consider in explaining runoff change, integrating land and water management, and informing water governance.
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Tree transpiration in the Amazon may enhance rainfall for downwind forests. Until now it has been unclear how this cascading effect plays out across the basin. Here, we calculate local forest transpiration and the subsequent trajectories of transpired water through the atmosphere in high spatial and temporal detail. We estimate that one-third of Amazon rainfall originates within its own basin, of which two-thirds has been transpired. Forests in the southern half of the basin contribute most to the stability of other forests in this way, whereas forests in the south-western Amazon are particularly dependent on transpired-water subsidies. These forest-rainfall cascades buffer the effects of drought and reveal a mechanism by which deforestation can compromise the resilience of the Amazon forest system in the face of future climatic extremes.
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Theory and evidence indicate that trees and other vegetation influence the atmospheric water-cycle in various ways. These influences are more important, more complex, and more poorly characterised than is widely realised. While there is little doubt that changes in tree cover will impact the water-cycle, the wider consequences remain difficult to predict as the underlying relationships and processes remain poorly characterised. Nonetheless, as forests are vulnerable to human activities, these linked aspects of the water-cycle are also at risk and the potential consequences of large scale forest loss are severe. Here, for non-specialist readers, I review our knowledge of the links between vegetation-cover and climate with a focus on forests and rain (precipitation). I highlight advances, uncertainties and research opportunities. There are significant shortcomings in our understanding of the atmospheric hydrological cycle and of its representation in climate models. A better understanding of the role of vegetation and tree-cover will reduce some of these shortcomings. I outline and illustrate various research themes where these advances may be found. These themes include the biology of evaporation, aerosols and atmospheric motion, as well as the processes that determine monsoons and diurnal precipitation cycles. A novel theory—the ‘biotic pump’—suggests that evaporation and condensation can exert a major influence over atmospheric dynamics. This theory explains how high rainfall can be maintained within those continental land-masses that are sufficiently forested. Feedbacks within many of these processes can result in non-linear behaviours and the potential for dramatic changes as a result of forest loss (or gain): for example, switching from a wet to a dry local climate (or visa-versa). Much remains unknown and multiple research disciplines are needed to address this: forest scientists and other biologists have a major role to play. New ideas, methods and data offer opportunities to improve understanding. Expect surprises.
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Although it is well established that transpiration contributes much of the water for rainfall over Amazonia, it remains unclear whether transpiration helps to drive or merely responds to the seasonal cycle of rainfall. Here, we use multiple independent satellite datasets to show that rainforest transpiration enables an increase of shallow convection that moistens and destabilizes the atmosphere during the initial stages of the dry-to-wet season transition. This shallow convection moisture pump (SCMP) preconditions the atmosphere at the regional scale for a rapid increase in rain-bearing deep convection, which in turn drives moisture convergence and wet season onset 2–3 mo before the arrival of the Intertropical Convergence Zone (ITCZ). Aerosols produced by late dry season biomass burning may alter the efficiency of the SCMP. Our results highlight the mechanisms by which interactions among land surface processes, atmospheric convection, and biomass burning may alter the timing of wet season onset and provide a mechanistic framework for understanding how deforestation extends the dry season and enhances regional vulnerability to drought.
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Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanity's ability to protect our planet's climate and life-sustaining functions. The substantial body of research we review reveals that forest, water and energy interactions provide the foundations for carbon storage, for cooling terrestrial surfaces and for distributing water resources. Forests and trees must be recognized as prime regulators within the water, energy and carbon cycles. If these functions are ignored, planners will be unable to assess, adapt to or mitigate the impacts of changing land cover and climate. Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority. For reasons of sustainability, carbon storage must remain a secondary, though valuable, by-product. The effects of tree cover on climate at local, regional and continental scales offer benefits that demand wider recognition. The forest-and tree-centered research insights we review and analyze provide a knowledge-base for improving plans, policies and actions. Our understanding of how trees and forests influence water, energy Adaptation Sustainability and carbon cycles has important implications, both for the structure of planning, management and governance institutions, as well as for how trees and forests might be used to improve sustainability, adaptation and mitigation efforts.
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Water scarcity contributes to the poverty of around one-third of the world’s people. Despite many benefits, tree planting in dry regions is often discouraged by concern that trees reduce water availability. Yet relevant studies from the tropics are scarce, and the impacts of intermediate tree cover remain unexplored. We developed and tested an optimum tree cover theory in which groundwater recharge is maximized at an intermediate tree density. Below this optimal tree density the benefits from any additional trees on water percolation exceed their extra water use, leading to increased groundwater recharge, while above the optimum the opposite occurs. Our results, based on groundwater budgets calibrated with measurements of drainage and transpiration in a cultivated woodland in West Africa, demonstrate that groundwater recharge was maximised at intermediate tree densities. In contrast to the prevailing view, we therefore find that moderate tree cover can increase groundwater recharge, and that tree planting and various tree management options can improve groundwater resources. We evaluate the necessary conditions for these results to hold and suggest that they are likely to be common in the seasonally dry tropics, offering potential for widespread tree establishment and increased benefits for hundreds of millions of people.
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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.
Many natural and social phenomena depend on river flow regimes that are being altered by global change. Understanding the mechanisms behind such alterations is crucial for predicting river flow regimes in a changing environment. Here we introduce a novel physical interpretation of the scaling properties of river flows and show that it leads to a parsimonious characterization of the flow regime of any river basin. This allows river basins to be classified as regulated or unregulated, and to identify a critical threshold between these states. We applied this framework to the Amazon river basin and found both states among its main tributaries. Then we introduce the forest reservoir hypothesis to describe the natural capacity of river basins to regulate river flows through land–atmosphere interactions (mainly precipitation recycling) that depend strongly on the presence of forests. A critical implication is that forest loss can force the Amazonian river basins from regulated to unregulated states. Our results provide theoretical and applied foundations for predicting hydrological impacts of global change, including the detection of early-warning signals for critical transitions in river basins.
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The global tree restoration potential
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Comment on "The global tree restoration potential" Joseph W. Veldman, Julie C. Aleman, Swanni T.
) that tree planting for climate change mitigation could sequester 205 gigatonnes of carbon is approximately five times too large. Their analysis inflated soil organic carbon gains, failed to safeguard against warming from trees at high latitudes and elevations
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Alvarado, T. Michael Anderson, Sally Archibald, William J. Bond, Thomas W. Boutton, Nina Buchmann, Elise Buisson, Josep G. Canadell, Michele de Sá Dechoum, Milton H. Diaz-Toribio, Giselda Durigan, John J. Ewel, G. Wilson Fernandes, Alessandra Fidelis, Forrest Fleischman, Stephen P. Good, Daniel M. Griffith, Julia-Maria Hermann, William A. Hoffmann, Soizig Le Stradic, Caroline E. R. Lehmann, Gregory Mahy, Ashish N. Nerlekar, Jesse B. Nippert, Reed F. Noss, Colin P. Osborne, Gerhard E. Overbeck, Catherine L. Parr, Juli G. Pausas, R. Toby Pennington, Michael P. Perring, Francis E. Putz, Jayashree Ratnam, Mahesh Sankaran, Isabel B. Schmidt, Christine B. Schmitt, Fernando A. O. Silveira, A. Carla Staver, Nicola Stevens, Christopher Still, Caroline A. E. Strömberg, Vicky M. Temperton, J. Morgan Varner, Nicholas P. Zaloumis Bastin et al.'s estimate (Reports, 5 July 2019, p. 76) that tree planting for climate change mitigation could sequester 205 gigatonnes of carbon is approximately five times too large. Their analysis inflated soil organic carbon gains, failed to safeguard against warming from trees at high latitudes and elevations, and considered afforestation of savannas, grasslands, and shrublands to be restoration. Full text:
76) neglect considerable research into forestbased climate change mitigation during the 1980s and 1990s. This research supports some of their findings on the area of land technically suitable for expanding tree cover and can be used to
  • Alan Grainger
  • Louis R Iverson
  • Gregg H Marland
  • Anantha Prasad Bastin
Comment on "The global tree restoration potential" Alan Grainger, Louis R. Iverson, Gregg H. Marland, Anantha Prasad Bastin et al. (Reports, 5 July 2019, p. 76) neglect considerable research into forestbased climate change mitigation during the 1980s and 1990s. This research supports some of their findings on the area of land technically suitable for expanding tree cover and can be used to extend their analysis to include the area of actually available land and operational feasibility.