Mega-blowouts in Qinghai–Tibet Plateau: morphology, distribution and initiation.

Blowouts are wind‐eroded landforms that are widely distributed in the north‐eastern part in Qinghai–Tibet Plateau (QTP), China. These blowouts are thought to form in response to climate change and/or human activity but little is known about their morphodynamics. Using field surveys, remote sensing and geographic information system (GIS) spatial analysis, the distribution and morphology of blowouts are analysed and their initiation considered. Results show the QTP mega‐blowouts are some of the largest in the world. The orientations of the trough shaped blowouts are parallel with the prevailing wind, but the saucer and bowl‐shaped blowouts are influenced by bi‐directional transport. Whilst regional patterns of blowout shape and size were observed to reflect the extent of aeolian sediments and wind regimes, the relationship between the different morphological parameters showed consistency. During initial stages of development, the length to width ratios of blowouts increase rapidly with area but after they reach a mega size this relationship stabilizes as blowouts widen. Initial luminescence dating shows that blowouts appear to have initiated ~100 to 500 years ago, coinciding with the Little Ice Age (LIA) climate event when northwest winds are known to have intensified. Further work is required to confirm this initiation period and establish the significance of mega blowouts for landscape degradation and human activities

Attribution of growing season evapotranspiration variability considering snowmelt and vegetation changes in the arid alpine basins

Previous studies have successfully applied variance decomposition frameworks based on the Budyko equations to determine the relative contribution of variability in precipitation, potential evapotranspiration (E0), and total water storage changes (ΔS) to evapotranspiration variance (σET2) on different timescales; however, the effects of snowmelt (Qm) and vegetation (M) changes have not been incorporated into this framework in snow-dependent basins. Taking the arid alpine basins in the Qilian Mountains in northwest China as the study area, we extended the Budyko framework to decompose the growing season σET2 into the temporal variance and covariance of rainfall (R), E0, ΔS,Qm, and M. The results indicate that the incorporation of Qm could improve the performance of the Budyko framework on a monthly scale; σET2 was primarily controlled by the R variance with a mean contribution of 63 %, followed by the coupled R and M (24.3 %) and then the coupled R and E0 (14.1 %). The effects of M variance or Qm variance cannot be ignored because they contribute 4.3 % and 1.8 % of σET2, respectively. By contrast, the interaction of some coupled factors adversely affected σET2, and the out-of-phase seasonality between R and Qm had the largest effect (−7.6 %). Our methodology and these findings are helpful for quantitatively assessing and understanding hydrological responses to climate and vegetation changes in snow-dependent regions on a finer timescale.</p

Mountain pastures of Qilian Shan: plant communities, grazing impact and degradation status (Gansu province, NW China)

Environmental degradation of pasture areas in the Qilian Mountains (Gansu province, NW China) has increased in recent years. Soil erosion and loss of biodiversity caused by overgrazing is widespread. Changes in plant cover, however, have not been analysed so far. The aim of this paper is to identify plant communities and to detect grazing-induced changes in vegetation patterns. Quantitative and qualitative releve data were collected for community classification and to analyse gradual changes in vegetation patterns along altitudinal and grazing gradients. Detrended correspondence analysis (DCA) was used to analyse variation in relationships between vegetation, environmental factors and differential grazing pressure. The results of the DCA showed apparent variation in plant communities along the grazing gradient. Two factors – altitude and exposure – had the strongest impact on plant community distribution. Comparing monitoring data for the most recent nine years, a trend of pasture deterioration, plant community successions and shift in dominant species becomes obvious. In order to increase grassland quality, sustainable pasture management strategies should be implemented

Variations and controlling factors of vegetation dynamics on the Qingzang Plateau of China over the recent 20 years

The impacts of climate change and human activities on vegetation dynamics have attracted wide attention, especially in sensitive and vulnerable areas such as the Qingzang Plateau of China. In this region, a series of ecological restoration projects have been launched while the effectiveness of these projects requires evaluation and further improvements. Remote sensing with high temporal resolution and spatial coverage is an effective way for the vegetation dynamics research in this region. In this study, the spatial and temporal distribution of climate factors and vegetation coverage as well as the influencing factors such as air temperature, precipitation, land use, slope, slope direction, soil and altitude were analyzed. The geographical detector was used to analyze the influence of climate factors on vegetation coverage and the interaction among factors in different eco-geographical regions. The results showed that: 1) the average values from the 20 years of normalized difference vegetation index (NDVI) decreased gradually from southeast (> 0.61) to northwest (0.12). The overall average of NDVI increased 0.02 per year from 1998 to 2018 and the impact factors varied among different eco-geographical regions; 2) some controlling factors showed nonlinear enhancement such as altitude and slope; 3) land use was an important factor affecting the distribution of vegetation especially in humid, semi-arid and arid areas, but the impacts of elevation and temperature were stronger than land use types in semi-humid and humid areas. The design and construction of ecological protection and restoration projects on the Qingzang Plateau required scientific and detailed demonstration as well as monitoring and evaluation. In addition, new tools and theories were also needed in the selection of ecosystem restoration strategies. Based on the findings, this study also provides suggestions for the sustainable ecological restoration on the Qingzang Plateau

Vegetation Dynamics Revealed by Remote Sensing and Its Feedback to Regional and Global Climate

This book focuses on some significant progress in vegetation dynamics and their response to climate change revealed by remote sensing data. The development of satellite remote sensing and its derived products offer fantastic opportunities to investigate vegetation changes and their feedback to regional and global climate systems. Special attention is given in the book to vegetation changes and their drivers, the effects of extreme climate events on vegetation, land surface albedo associated with vegetation changes, plant fingerprints, and vegetation dynamics in climate modeling

Pedogenesis, Permafrost, and Ecosystem Functioning: Feedbacks and Interactions along Climate Gradients across the Tibetan Plateau

This thesis was conducted within the scope of a graduation fellowship from the state of Baden-Württemberg, Germany (Grant No.: VI 4.2-7631.2/Baumann) in cooperation with the Depart-ment of Ecology, Peking University, Beijing. Scientists specialised in both ecology and soil science investigated the same sites, thus allowing an interdisciplinary approach to evaluate soil properties, C and N cycles as well as geomorphological processes in close connection to ecosys-tem interrelations on the Tibetan Plateau. The research sites are located along a 1,200 km long north-south transect at altitudes between 2,925 and 5,105 m ASL. Two thirds of the Tibetan Plateau is influenced by permafrost. Due to the high sensitivity to global climate warming and land use changes, permafrost degradation processes are widespread, increasing the heterogeneity of soil formation, soil hydrology, and related soil chemical processes (i.e. C and N cycling). In order to account for the resulting extremely diverse ecosystem, investigations at different spatial scales related to large-scale climate patterns were performed. The scales comprise the total main transect, the split transect into an eastern and western section, diverse catenas along distinct geomorphological relief units, and finally the single site soil profiles. The first part of this work examines C and N contents as well as portions of plant available min-eralised nitrogen in relation to their main influencing parameters. For investigations on land-scape scale, soil moisture was found to have the strongest effect on C and N cycling, followed by CaCO3-content and soil texture. Altogether, the general linear model explains 64% and 60% of the variation of soil organic carbon (SOC) and total nitrogen (NT) contents, respectively. Thereby, two aspects are important: (1) temperature variables have no significant influence and (2) indicators for soil development (i.e. CaCO3 and soil texture) are included besides commonly con-sidered ecological (i.e. moisture, temperature and biomass) parameters. It could be shown that in the highly diverse permafrost-affected ecosystem of the Tibetan Plateau, other factors than precipitation mainly control soil moisture contents and distribution, with permafrost and relief position being the most dominant parameters. Since pedogenic parameters turned out to be important predictors, the degree of soil development can be regarded as an additional control quantity, indicating higher C and N contents of topsoils with longer duration of undisturbed and stable soil development. Mineralised plant available N can be almost exclusively found as am-monium-N, which is closely related to higher soil moisture contents and frigid climate condi-tions, showing by far the highest contents in the permafrost main soil group. As nitrification is strongly temperature dependent, nitrate-N contents are correspondingly very low. The results provide clear evidence that limitation in plant available nutrients as a negative feedback to lower soil moisture is crucial for plant growth in nutrient-limited alpine grassland ecosystems, even though higher temperatures occur with respect to climate warming. Importantly, these strong feedback mechanisms between altering permafrost conditions (degradation and higher active layer thickness) and hence reverse influence of rising temperatures (further decay of permafrost and related dryer conditions) could be only detected by conducting this study on landscape scale. These dependencies are based on the overall limitation of moisture, because evaporation exceeds precipitation by far at all investigated sites. Degraded permafrost profiles show low C and N contents combined with distinct depth patterns, mainly caused by higher mineralisation rates and deposition of proximal airborne sediments. This is can be exemplarily shown for the Shule River basin located at the very north-eastern margin of the Tibetan Plateau, where soils under desert-type vegetation have their highest SOC density in soil depths between 20 and 40 cm, but not in the top 20 cm as evident for all other vegetation types. The main reason for these patterns are most likely such syngenetic soil forming processes. Results of soil respiration measurements basically confirm the findings observed for C and N contents. Belowground biomass and soil moisture explain 82% of the variation, whereas no direct effects of temperature could be described. Respiration values of alpine meadows were 2.5 times higher than of alpine steppes, which is a consequence of higher biomass and productivity in alpine meadows. Besides the relations to control variables, SOC was further analysed with regard to its stocks and composition. The comparison of two main investigation sites for discontinuous and continuous permafrost, respectively, clearly shows higher SOC stocks for discontinuous (10.4 kg m-2) than for continuous permafrost (3.4 kg m-2). Highest values occur at water-saturated profiles (19.3 kg m-2), causing positive feedbacks to even higher SOC accumulation, if in turn denser vegetation isolates the soil. At the same time, these soils contain substantial higher portions of easily de-composable particulate organic matter fractions, which are especially vulnerable to climate change owing to shorter turnover rates. The colder and dryer climate in continuous permafrost areas leads to a lower productivity and an allocation of belowground biomass mainly in the top 10 cm. This can be approved by studies conducted in the Shule River basin, also characterised by low mean annual temperature and precipitation, showing average SOC stocks of 7.7 kg m-2. Moreover, different vegetation types can be distinguished very clearly, ranging from 4.4 kg m-2 under desert vegetation to 19.8 kg m-2 under partly water-saturated alpine swamp meadow (cf. above-mentioned corresponding respiration rates related to vegetation type patterns). Moreover, it could be shown that soil inorganic carbon (SIC) and SOC are influenced by different parameter sets. Whereas soil physical and chemical properties are most appropriate to describe SIC, biotic and climatic factors are more important for SOC. Soil pH was found to predict 42% of SIC variation, leading to lower contents with decreasing pH. However, the overall effect of the released carbon under scenarios of potential soil acidification is assumed to be compensated, since SOC reacts vice versa to increased soil acidity. Since pedological processes proved to have significant influence on C and N contents, it is im-portant to specifically qualify related weathering and sedimentation processes depending on the state of permafrost as well as land surface stability. To address this issue, weathering indices and pedogenic Fe-oxides were applied to particular sampling groups, distinctly influenced by the Indian and Asian Monsoon systems. The chemical index of alteration (CIA) represents the most useful weathering index, best describing large scale climate trends, varieties of substrates, and specific permafrost patterns. For pedogenic Fe-oxides, (Fed-Feo)/Fet ratio best illustrates small-scale shifts of pedogenesis. This can be confirmed by the differentiability of the main soil groups, which cannot be obtained by CIA. Essentially, groundwater and permafrost influenced soils can be clearly distinguished by distinct parameter sets best explaining each soil group: climate pa-rameters for the permafrost soil group (climate-zonal soil formation), and site-specific variables for groundwater-influenced soils (azonal soil formation). Moreover, the two soil groups can be significantly differentiated by Fep, even though both show high soil moisture and SOC contents. Therefore it can be assumed, that particular redoxi-morphic and soil formation processes with corresponding soil organic matter structures evolve under the influence of permafrost. Alto-gether, the application at various spatial scales give strong evidence that weathering indices and pedogenic Fe-oxides are useful tools to depict states of permafrost distribution and its degrada-tion features. Summarising, the described geochemical patchwork (manuscripts 1-5) can be disentangled by applying weathering indices and pedogenic oxides ratios, depending on the scale and process. Together with the evaluation of the prevailing main influencing parameters, they proved to be crucial for assessing C and N cycles and ecosystem functioning on the Tibetan Plateau.Die vorliegende Arbeit wurde im Rahmen eines Stipendiums der Landesgraduiertenförderung Baden-Württemberg (Förderungs-Nr.: VI 4.2-7631.2/Baumann) in Zusammenarbeit mit der Fakultät für Ökologie der Peking University erstellt. Somit waren interdisziplinäre Untersuchun-gen von Bodeneigenschaften, C- und N-Kreislauf, geomorphologischen Prozessen sowie die di-rekte Analyse der Wechselbeziehungen dieser Parameter zum Gesamtökosystem des Tibetischen Hochplateaus möglich. Die Forschungsstandorte liegen entlang eines 1200 km langen nord-süd verlaufenden Transekts in Höhen zwischen 2925 und 5105 m ü. NN. Ungefähr zwei Drittel des Tibetischen Hochplateaus sind durch Permafrost beeinflusst und entsprechend besonders empfindlich im Hinblick auf Klimawandel und Landnutzungswechsel. Folglich sind häufig großräumige Degradationsprozesse zu beobachten. Dies führt zu einer steigenden Heterogenität der Bodenbildung, Bodenhydrologie und nachgeordneten bodenchemischen Prozessen, deren wichtigster Bestandteil der C- und N-Kreislauf ist. Um dem resultierenden, extrem diversen Ökosystem in seiner gesamten Breite gerecht zu werden, wurden Analysen auf verschiedenen räumlichen Maßstabsebenen entlang von Klimagradienten durchgeführt. Die Maßstabsebenen umfassen den gesamten Haupttransekt, einen östlichen und westlichen Teiltransekt, diverse Catenen entlang bestimmter geomorphologischer Reliefeinheiten und die Einzelstandorte. Zunächst wurden C- und N-Gehalte sowie die Anteile pflanzenverfügbaren Stickstoffs in Verbin-dung mit deren Haupteinflussparametern untersucht. Auf Landschaftsebene hat Bodenfeuchte den größten Einfluss auf die C- und N-Gehalte, gefolgt von CaCO3 und der Korngrößenverteilung. Insgesamt erklärt das lineare Regressionsmodell 64% der Variation von organischen Bodenkoh-lenstoffgehalten (SOC) und 60% in Bezug auf den Gesamtstickstoff (TN). Dabei ist zweierlei maßgeblich: (1) Temperaturvariablen haben keinen signifikanten Einfluss, während (2) Indika-toren der Bodengenese, wie CaCO3-Gehalt und Korngrößenverteilung neben herkömmlichen ökologischen Variablen, wie beispielsweise Feuchtigkeitsparameter oder Biomasse, in das Re-gressionsmodell aufgenommen werden. Entsprechend wird in den hoch komplexen, periglazial geprägten Ökosystemen des Tibetischen Hochplateaus die Bodenfeuchteverteilung nicht direkt durch den Niederschlag, sondern vielmehr durch die auf indirektem Wege agierenden Parameter Reliefposition und Permafrost kontrolliert. Da sich bodenkundliche Einflussgrößen als wichtige Prädiktoren herausgestellt haben, kann der Grad der Bodenentwicklung allgemein als eine zusätzliche Stellgröße betrachtet werden: Je länger eine ungestörte und stabile Pedogenese vor-liegt, desto höhere C- und N-Gehalte sind zu beobachten. Dies betrifft auch den mineralisierten pflanzenverfügbaren Stickstoff, der fast ausschließlich als Ammonium-N vorliegt, was wiederum eng an erhöhte Bodenfeuchte und kühle Klimaverhältnisse geknüpft ist. Dabei treten die mit Abstand höchsten Werte in der Hauptbodengruppe „Permafrost“ auf. Entsprechend weist Nitrat-N sehr geringe Gehalte auf, da Nitrifikationsprozesse stark temperaturabhängig sind. Die Ergeb-nisse liefern einen klaren Nachweis dafür, dass eine Limitierung pflanzenverfügbarer Nährstoffe als negative Rückkopplung aufgrund geringerer Bodenfeuchtewerte trotz potenziell steigender Temperaturen im Hinblick auf die globale Erwärmung hervorgerufen werden kann. Die ausge-prägten Rückkopplungsmechanismen zwischen Veränderungen des Permafrosts (Degradations-prozesse und größere Mächtigkeit des Active Layers) und infolgedessen eines umgekehrten Ein-flusses steigender Temperatur (weiterer Rückgang von Permafrost und damit verbundene tro-ckenere Bedingungen) konnten ausschließlich aufgrund des gewählten Maßstabs auf Land-schaftsebene ermittelt werden. Diese Abhängigkeiten basieren auf der negativen Feuchtigkeits-bilanz des Untersuchungsgebietes, da die Evaporation bei weitem die Niederschlagswerte über-steigt. Die niedrigen C- und N-Gehalte sowie die spezifische Tiefenverteilung an degradierten Standorten sind hauptsächlich auf höhere Mineralisationsraten und die Ablagerung von proximal generierten äolischen Sedimenten zurückzuführen. Dies kann exemplarisch für das Einzugsgebiet des Shule River am nordöstlichen Rand des Tibetischen Hochplateaus aufgezeigt werden, wo Böden unter Wüstenvegetation nicht wie alle anderen Vegetationstypen die höchsten SOC-Gehalte in den ersten 20 cm, sondern vielmehr in Bodentiefen zwischen 20 und 40 cm aufweisen. Hauptgrund hierfür sind ebendiese synsedimentären Bodenbildungen. Ergebnisse von Bo-denrespirationsmessungen bestätigen grundsätzlich die für C und N-Gehalte gemachten Be-obachtungen. Unterirdische Biomasse und Bodenfeuchte erklären 82% der Gesamtvariation, wobei kein direkter Einfluss von Temperatur nachgewiesen werden konnte. Die Bodenrespira-tion alpiner Matten übersteigt aufgrund der höheren Biomasse und Produktivität die von alpiner Steppenvegetation um das 2,5-fache. Neben den Beziehungen mit Kontrollvariablen wurde SOC zusätzlich im Hinblick auf Vorräte und Zusammensetzung untersucht. Der Vergleich zwischen den Hauptuntersuchungsstandorten erbrachte deutlich höhere SOC-Vorräte für diskontinuierlichen Permafrost (10.4 kg m-2), wäh-rend im kontinuierlichen Permafrost lediglich durchschnittlich 3.4 kg m-2 ermittelt wurden. Höchste Vorräte finden sich in wassergesättigten Profilen (19.3 kg m-2), da die Isolationswirkung der dichteren Vegetation einen positiven Rückkopplungsmechanismus auslösen und zu einer weiteren Akkumulation von SOC führen kann. Gleichzeitig enthalten diese Böden im Bereich des diskontinuierlichen Permafrosts höhere Anteile an vergleichsweise leicht abbaubaren Fraktionen partikulärer organischer Substanz, die entsprechend anfällig auf Klimaveränderungen reagiert. Die kühleren und trockeneren Verhältnisse im Bereich des kontinuierlichen Permafrosts führen hingegen zu einer geringeren Produktivität und einer schwerpunktmäßigen Verteilung der unterirdischen Biomasse in den obersten 10 cm. Dies kann zusätzlich durch Untersuchungen im ebenfalls durch niedrige Jahresdurchschnittstemperaturen und Niederschlägen geprägten Einzugsgebiet des Shule River nachgewiesen werden. Hier finden sich durchschnittliche SOC-Vorräte von 7.7 kg m-2, die je nach Vegetationseinheit zwischen 4.4 kg m-2 unter Wüstenvegeta-tion und 19.8 kg m-2 unter wassergesättigten alpinen Sumpfmatten variieren (vgl. oben be-schriebene Respirationswerte in Bezug auf verschiedene Vegetationsmuster). Ferner konnte gezeigt werden, dass anorganischer Kohlenstoff (SIC) und SOC durch unter-schiedliche Parametersets beeinflusst werden: Bodenphysikalische und bodenchemische Eigen-schaften beschreiben SIC am besten, während biotische und klimatische Faktoren für SOC rele-vanter sind. Ein niedrigerer pH-Wert führt demnach zu geringeren SIC-Gehalten und erklärt 42% der Variation. Jedoch kann im Hinblick auf potentielle Bodenversauerung die Kohlen-stofffreisetzung aufgrund der umgekehrten Reaktion von SOC kompensiert werden. Da ein signifikanter Einfluss bodenbildender Prozesse auf C- und N-Gehalte nachgewiesen wer-den konnte, ist es notwendig damit verbundene Verwitterungs- und Sedimentationsprozesse in Bezug auf Permafrostverteilung und Oberflächenstabilität zu analysieren. Hierfür wurden Ver-witterungsindizes und pedogene Fe-Oxide auf verschiedenen Maßstabsebenen und Untergruppen in Bezug auf spezifische klimatische Verhältnisse angewendet. Der „chemical index of alteration“ (CIA) eignet sich dabei am besten um großräumige Klimatrends, Substratunterschiede und spezifische Permafrostverteilungsmuster zu beschreiben. Dagegen zeigen Quotienten pedogener Fe-Oxide kleinräumige bodengenetische Wechsel an, wofür sich vorzugsweise (Fed-Feo)/Fet bewährt hat. Dies kann durch die klare Differenzierbarkeit von Hauptbodengruppen, die durch den CIA nicht möglich ist, untermauert werden. Dabei ist wesentlich, dass Böden, die durch Grundwasser und Permafrost beeinflusst sind, klar zu unterscheiden sind. Klimaparameter haben innerhalb der Hauptbodengruppe „Permafrost“ das größte Gewicht (klimazonale Bodenbildung), während standortspezifische Variablen den Haupteinfluss innerhalb von Grundwasser geprägten Böden aufweisen (azonale Bodenbildung). Zusätzlich können diese Bodengruppen statistisch signifikant durch Fep unterschieden werden, obwohl sie ähnlichen SOC-Gehalten und Bodenfeuchteverhältnissen unterliegen. Folglich entsteht in Permafrost beeinflussten Böden aufgrund bestimmter redoximorpher und bodenbildender Prozesse organische Substanz mit spezifischen Strukturen und Eigenschaften. Insgesamt erweisen sich Verwitterungsindices und pedogene Fe-Oxide als vielversprechende Werkzeuge um diverse Stadien des Permafrosts, des-sen räumliche Verteilung und Fragen der Oberflächenstabilität zu analysieren. Die hohe kleinräumige, geochemische Variabilität (Manuskripte 1-5) kann durch den Einsatz von Verwitterungsindices und pedogenen Oxiden (Manuskript 6) je nach Maßstabsebene und zu beurteilenden Prozessen entflochten werden. Zusammen mit den dargestellten Haupteinfluss-parametern auf C- und N-Kreisläufe ist eine umfassende Beurteilung der Ökosystemfunktionen des Tibetischen Hochplateaus möglich

Water Resource Variability and Climate Change

Climate change affects global and regional water cycling, as well as surficial and subsurface water availability. These changes have increased the vulnerabilities of ecosystems and of human society. Understanding how climate change has affected water resource variability in the past and how climate change is leading to rapid changes in contemporary systems is of critical importance for sustainable development in different parts of the world. This Special Issue focuses on “Water Resource Variability and Climate Change” and aims to present a collection of articles addressing various aspects of water resource variability as well as how such variabilities are affected by changing climates. Potential topics include the reconstruction of historic moisture fluctuations, based on various proxies (such as tree rings, sediment cores, and landform features), the empirical monitoring of water variability based on field survey and remote sensing techniques, and the projection of future water cycling using numerical model simulations

Energy and Water Cycles in the Third Pole

As the most prominent and complicated terrain on the globe, the Tibetan Plateau (TP) is often called the “Roof of the World”, “Third Pole” or “Asian Water Tower”. The energy and water cycles in the Third Pole have great impacts on the atmospheric circulation, Asian monsoon system and global climate change. On the other hand, the TP and the surrounding higher elevation area are also experiencing evident and rapid environmental changes under the background of global warming. As the headwater area of major rivers in Asia, the TP’s environmental changes—such as glacial retreat, snow melting, lake expanding and permafrost degradation—pose potential long-term threats to water resources of the local and surrounding regions. To promote quantitative understanding of energy and water cycles of the TP, several field campaigns, including GAME/Tibet, CAMP/Tibet and TORP, have been carried out. A large amount of data have been collected to gain a better understanding of the atmospheric boundary layer structure, turbulent heat fluxes and their coupling with atmospheric circulation and hydrological processes. The focus of this reprint is to present recent advances in quantifying land–atmosphere interactions, the water cycle and its components, energy balance components, climate change and hydrological feedbacks by in situ measurements, remote sensing or numerical modelling approaches in the “Third Pole” region

Afforestation and Reforestation: Drivers, Dynamics, and Impacts

Afforestation/reforestation (or forestation) has been implemented worldwide as an effective measure towards sustainable ecosystem services and addresses global environmental problems such as climate change. The conversion of grasslands, croplands, shrublands, or bare lands to forests can dramatically alter forest water, energy, and carbon cycles and, thus, ecosystem services (e.g., carbon sequestration, soil erosion control, and water quality improvement). Large-scale afforestation/reforestation is typically driven by policies and, in turn, can also have substantial socioeconomic impacts. To enable success, forestation endeavors require novel approaches that involve a series of complex processes and interdisciplinary sciences. For example, exotic or fast-growing tree species are often used to improve soil conditions of degraded lands or maximize productivity, and it often takes a long time to understand and quantify the consequences of such practices at watershed or regional scales. Maintaining the sustainability of man-made forests is becoming increasingly challenging under a changing environment and disturbance regime changes such as wildland fires, urbanization, drought, air pollution, climate change, and socioeconomic change. Therefore, this Special Issue focuses on case studies of the drivers, dynamics, and impacts of afforestation/reforestation at regional, national, or global scales. These new studies provide an update on the scientific advances related to forestation. This information is urgently needed by land managers and policy makers to better manage forest resources in today’s rapidly changing environments