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Fire is a widespread agent of disturbance in African drylands, but the impact of fire on local precipitation remains poorly understood and large-scale observational evidence has been lacking. Here we link fire to a reduction in precipitation across African drylands. Using 15 years of satellite observations over continental sub-Saharan Africa, we find that more extensive and later dry season fires lead to wet season rainfall deficits of up to 30 mm (~10%). The effect is stronger in the Southern Hemisphere, a signal we attribute to the later timing of fires in the dry season. Given the coupling between rainfall, fuel loads, and fire in African drylands, a negative interannual feedback may arise between fire and precipitation, whereby fires suppress precipitation, thereby reducing fuel load and fire in the subsequent season. The reduced fuel load would, in turn, increase precipitation, completing the feedback loop. This feedback may contribute to a pervasive negative autocorrelation observed in Southern Hemisphere annual rainfall.

Meeting the food needs of the growing and increasingly affluent human population with the planet’s limited resources is a major challenge of our time. Seen as the preferred approach to global food security issues, ‘sustainable intensification’ is the enhancement of crop yields while minimizing environmental impacts and preserving the ability of future generations to use the land. It is still unclear to what extent sustainable intensification would allow humanity to meet its demand for food commodities. Here we use the footprints for water, nitrogen, carbon and land to quantitatively evaluate resource demands and greenhouse gas (GHG) emissions of future agriculture and investigate whether an increase in these environmental burdens of food production can be avoided under a variety of dietary scenarios. We calculate average footprints of the current diet and find that animal products account for 43–87% of an individual’s environmental burden – compared to 18% of caloric intake and 39% of protein intake. Interestingly, we find that projected improvements in production efficiency would be insufficient to meet future food demand without also increasing the total environmental burden of food production. Transitioning to less impactful diets would in many cases allow production efficiency to keep pace with growth in human demand while minimizing the food system’s environmental burden. This study provides a useful approach for evaluating the attainability of sustainable targets and for better integrating food security and environmental impacts.

In shallow coastal bays where nutrient loading and riverine inputs are low, turbidity, and the consequent light environment are controlled by resuspension of bed sediments due to wind-waves and tidal currents. High sediment resuspension and low light environments can limit benthic primary productivity; however, both currents and waves are affected by the presence of benthic plants such as seagrass. This feedback between the presence of benthic primary producers such as seagrass and the consequent light environment has been predicted to induce bistable dynamics locally. However, these vegetated areas influence a larger area than they footprint, including a barren adjacent downstream area which exhibits reduced shear stresses. Here we explore through modeling how the patchy structure of seagrass meadows on a landscape may affect sediment resuspension and the consequent light environment due to the presence of this sheltered region. Heterogeneous vegetation covers comprising a mosaic of randomly distributed patches were generated to investigate the effect of patch modified hydrodynamics. Actual cover of vegetation on the landscape was used to facilitate comparisons across landscape realizations. Hourly wave and current shear stresses on the landscape along with suspended sediment concentration and light attenuation characteristics were then calculated and spatially averaged to examine how actual cover and mean water depth affect the bulk sediment and light environment. The results indicate that an effective cover, which incorporates the sheltering area, has important controls on the distributions of shear stress, suspended sediment, light environment, and consequent seagrass habitat suitability. Interestingly, an optimal habitat occurs within a depth range where, if actual cover is reduced past some threshold, the bulk light environment would no longer favor seagrass growth.

We investigate the influence of vegetation on river morphological instabilities using an analytical framework. We first discuss the important role of the hydrological (flooding frequency) and biological (vegetation development rate) timescales. As long as the changes in riverbed morphology and vegetation over an interval comprising one flood and one low-flow period are small, we show that it is possible to simplify the description of a vegetated river with non-constant discharge. We propose physically-based and effective (neural) models for the feedback between vegetation and morphodynamics. Physically-based approaches use equations of morphodynamics extended to account for the interplay between flow, sediment and vegetation dynamics. While their foundation is solid, a physically-based description is only feasible for simple vegetation cover (grass to shrubs). For complex vegetated obstacles we present as an alternative effective approaches, explicitly including interactions (local and non-local) between obstacles. We focus on the role of vegetation in the emergence of ridge patterns observed in the presence of an ephemeral flow and correspondingly derive a set of conditions for patterns. (C) 2015 Elsevier Ltd. All rights reserved.

The Florida Everglades freshwater landscape exhibits a distribution of islands covered by woody vegetation and bordered by marshes and wet prairies. Known as “tree islands”, these ecogeomorphic features can be found in few other low gradient, nutrient limited freshwater wetlands. In the last few decades, however, a large percentage of tree islands have either shrank or disappeared in apparent response to altered water depths and other stressors associated with human impacts on the Everglades. Because the processes determining the formation and spatial organization of tree islands remain poorly understood, it is still unclear what controls the sensitivity of these landscapes to altered conditions. We hypothesize that positive feedbacks between woody plants and soil accretion are crucial to emergence and decline of tree islands. Likewise, positive feedbacks between phosphorus (P) accumulation and trees explain the P enrichment commonly observed in tree island soils. Here, we develop a spatially-explicit model of tree island formation and evolution, which accounts for these positive feedbacks (facilitation) as well as for long range competition and fire dynamics. It is found that tree island patterns form within a range of parameter values consistent with field data. Simulated impacts of reduced water levels, increased intensity of drought, and increased frequency of dry season/soil consuming fires on these feedback mechanisms result in the decline and disappearance of tree islands on the landscape.

ECOHYDROLOGY Ecohydrol. (2016) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/eco.1742 Potential of grass invasions in desert shrublands to create novel ecosystem states under variable climate Kailiang Yu, 1 * Gregory S. Okin, 2 Sujith Ravi 3 and Paolo D’Odorico 1,4 Department of Environmental Sciences, University of Virginia, Charlottesville, VI, USA Department of Geography, University of California, Los Angeles, CA, USA Department of Earth and Environmental Sciences, Temple University, Philadelphia, PA, USA National Socio-Environmental Synthesis Center, University of Maryland, Annapolis, MD, USA ABSTRACT The invasion of exotic grasses into shrublands is a major disturbance to dryland ecosystems. The presence of exotic grasses enhances the occurrence of wildfire in landscapes that had not evolved in the presence of fire, leading to high rates of mortality of the native vegetation. Exotic grasses could be more prone to water stress and mortality than the shrubs they replaced and may not establish during drought, facts that are crucial in ecosystems undergoing increased climatic variability. Here, we develop a process-based modelling framework to investigate the complex dynamics resulting from the introduction of exotic grasses under variable climate. We find that the system converges towards different steady states, depending on the magnitude of climatic variability. While in the absence of climate fluctuations the shrubland state is replaced by an exotic grassland, interannual climate variability may inhibit grass invasion and stabilize the shrubland state. However, climatic variability also gives rise to a novel third, unvegetated state, with grass invasion being followed by drought, grass mortality and intense soil erosion. Most of the research on climate change effects on ecosystems has historically concentrated on the ecological impact of shifts in mean climate conditions. This study shows that changes in the variance are also important when shifts in vegetation composition (e.g. species invasions) result in different susceptibility to climatic variability. In the presence of random climate fluctuations, ecosystems can display steady states that differ from those that would exist under a constant climate or with a climate trend. Copyright © 2016 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article. KEY WORDS invasive species; fire cycle; climate variability; exotic grasses; unvegetated state Received 15 October 2015; Revised 18 March 2016; Accepted 28 March 2016 INTRODUCTION Biological invasions are recognized as major contributors to global environmental change (Vitousek et al., 1997; Mooney and Cleland, 2001). It has been observed that biological invasions affect ecosystem dynamics not only through their direct impact on resource competition and pool of available species (e.g. Olsson et al., 2012) but also indirectly through their ability to modify the disturbance regime. For example, invasive plants may change fire intensity and frequency or alter the rate of abiotic processes such as soil erosion (D’Antonio and Vitousek, 1992; Ziska et al., 2005; Miller et al., 2010). This disturbance-mediated effect of species invasions on ecosystems is observed when the invader is functionally different from the native species, *Correspondence to: Kailiang Yu, Department of Environmental Sciences, University of Virginia, Charlottesville, VI, USA. E-mail: ky9hc@virginia.edu Copyright © 2016 John Wiley & Sons, Ltd. i.e. when it exhibits some traits that (i) affect the disturbance regime and (ii) are missing in the native population (D’Antonio, 2000). For example, the invasion of desert shrublands by exotic annual and perennial grasses has been observed to lead to an increase in fire frequency and intensity because of the increase in grass fuel and in connectivity of vegetation cover (Okin et al., 2009a). The introduction of fires in shrubland ecosystems, where burning has not been historically a major selective force, results in an increase in the mortality rates of shrubland species, particularly if they are not adapted to fire (e.g. Bond et al., 2005; Runyan et al., 2012). The loss of shrub biomass further enhances the establishment and spread of invasive grasses (D’Antonio, 2000). Known as ‘the fire cycle’ (D’Antonio and Vitousek, 1992), this positive feedback leads to the replacement of fire-intolerant native shrubs with exotic grasses (Figure 1). The grass-fire feedback may induce stable grass-dominated vegetated states in arid and semiarid environments (Grigulis et al., 2005; Keeley and Rundel, 2005), even when shrubs have

© 2016 Elsevier Ltd. The environmental impact of the production and consumption of food is seldom depicted to consumers. The footprint of food products provides a means for consumers to compare environmental impacts across and within product groups. In this study we apply carbon, nitrogen, and water footprints in tandem and present food labels that could help inform consumers about the environmental impacts of individual food products. The footprint factors used in this study are specific to the United States, but the concept can be applied elsewhere. We propose three methods of footprint calculations: footprint weight, sustainability measures, and % daily value. We apply the three footprint calculation methods to four example labels (stars label, stoplight label, nutrition label add-on, and a detailed comparison label) that vary in design and the amount of detail provided. The stars label is simple and easily understood but provides minimal detail about the footprints. At the other end of the spectrum, the detailed comparison label gives context in relative terms (e.g., carbon emissions for equivalent distance driven) for the food product. Implementing environmental impact food labels requires additional understanding of how consumers use footprint labels, and label suitability may vary for government organizations, retail and local grocers, and farmers.

Meeting the increasing global demand for agricultural products without depleting the limited resources of the planet is a major challenge that humanity is facing. Most studies on global food security do not make projections past the year 2050, just as climate change and increasing demand for food are expected to intensify. Moreover, past studies do not account for the water sustainability limits of irrigation expansion to presently rainfed areas. Here we perform an integrated assessment that considers a range of factors affecting future food production and demand throughout the 21st century. We evaluate the self-sufficiency of 165 countries under sustainability, middle-of-the-road, and business-as-usual scenarios considering changes in diet, population, agricultural intensification, and climate. We find that under both the middle-of-the-road and business-as-usual trajectories global food self-sufficiency is likely to decline despite increased food production through sustainable agricultural intensification since projected food demand exceeds potential production. Contrarily, under a sustainability scenario, we estimate that there will be enough food production to feed the global population. However, most countries in Africa and the Middle East will continue to be heavily reliant on imports throughout the 21st century under all scenarios. These results highlight future hotspots of crop production deficits, reliance on food imports, and vulnerability to food supply shocks.

Referring to the analytical definition of water wars, several scholars have coherently argued against the “water leads to war thesis.” There are four arguments that have contributed to successfully dispel the myths of water wars: (a) interstate cooperation prevails over conflict; (b) development of new technologies increases freshwater availability; (c) the intrinsic characteristics of water as a resource do not justify interstate military intervention; (d) virtual water trade provides the opportunity to circumvent local water scarcity. These arguments converge demonstrating that rather than water wars in the future, water peace will prevail. While we agree with these arguments on the low likelihood of future water wars, we find that hydropolitical theories have generally neglected the fact that the conditions for interstate water peace come with high socio‐environmental costs. In particular, the central idea that virtual water trade resolve issues of local water scarcity and therefore reduces tensions and escalation of violence among different countries does not fully take into account the fact that dynamics of transnational water appropriation have serious socio‐environmental impacts on the virtual water exporting countries. To conceptualize this phenomenon we introduce the notion of “hidden socio‐environmental costs of virtual water transfer,” which is understood as a specific form of environmental cost‐shifting. The empirical support to our reasoning comes from the study of transnational large‐scale land acquisitions which represent an expanding phenomenon central in the contemporary global agrarian transformation.

The inherent interlinkages between food, energy, and water systems present both challenges and opportunities for a more sustainable future on Planet Earth.

Author(s): Davis, KF; Bhattachan, A; D'Odorico, P; Suweis, S | Abstract: Climate change is expected to impact the habitability of many places around the world in significant and unprecedented ways in the coming decades. While previous studies have provided estimates of populations potentially exposed to various climate impacts, little work has been done to assess the number of people that may actually be displaced or where they will choose to go. Here we modify a diffusion-based model of human mobility in combination with population, geographic, and climatic data to estimate the sources, destinations, and flux of potential migrants as driven by sea level rise (SLR) in Bangladesh in the years 2050 and 2100. Using only maps of population and elevation, we predict that 0.9 million people (by year 2050) to 2.1 million people (by year 2100) could be displaced by direct inundation and that almost all of this movement will occur locally within the southern half of the country. We also find that destination locations should anticipate substantial additional demands on jobs (594 000), housing (197 000), and food (783 × 109 calories) by mid-century as a result of those displaced by SLR. By linking the sources of migrants displaced by SLR with their likely destinations, we demonstrate an effective approach for predicting climate-driven migrant flows, especially in data-limited settings.

© 2017 Elsevier Ltd The increasing global demand for natural rubber (100% increase in the last 15 years) is for most part met by Malaysia and Indonesia, and – to a lesser extent – other countries in South-East Asia and Africa. The consequent expansion of rubber plantation has often occurred at the expenses of agricultural land for staple crops, particularly in South-East Asia, where 90% of the land suitable for agriculture is already under cultivation. Here we investigate the extent to which the ongoing increase in rubber production is competing with the food system and affecting the livelihoods of rural communities living in the production areas and their appropriation of natural resources, such as water. We also investigate to what extent the expansion of rubber plantations is taking place through large scale land acquisitions (LSLAs) and evaluate the impacts on rural communities. Our results show how rubber production needs more than 10 million ha of fertile land and up to 136–149 × 109m3y−1of freshwater (125 × 109m3y−1of green water and 11–24 × 109m3y−1of blue water). These resources would be sufficient to produce enough food to significantly reduce malnourishment in Indonesia, Thailand, and Vietnam if replaced by rice production. Overall, natural rubber production has important environmental, social, and economic impacts. Indeed, despite their ability to bring employment and increase the average income of economically disadvantaged areas, rubber plantations may threaten the local water and food security and induce a loss of rural livelihoods – particularly when the new plantations result from LSLAs that displace semi-subsistence forms of production – thereby forcing the local populations to depend on global food markets.

Large-scale acquisitions of agricultural land in developing countries have been rapidly increasing in the last 10 years, contributing to a major agrarian transition from subsistence or small scale farming to large-scale com- mercial agriculture by agribusiness transnational corporations. Likely driven by recent food crises, new bioenergy policies, and financial speculations, this phenomenon has been often investigated from the economic develop- ment, human right, land tenure and food security perspectives, while its hydrologic implications have remained understudied. It has been suggested that a major driver of large-scale land acquisitions (LSLAs) is the quest for water resources that can be used (locally) to sustain agricultural production in the acquired land. The appropri- ation of water resources associated with LSLAs has often been termed ‘water grabbing’, though to date a formal definition of such a normative and inherently pejorative term is missing. The intrinsic assumption is that the ac- quisition of water undergoes the same dynamics of unbalanced power relationships that underlie many LSLAs. Here we invoke hydrological theories of “green” and “blue” water flows to stress the extent to which water ap- propriations are inherently coupled to land acquisitions and specifically focus on blue water. We then propose a formal definition of blue water grabbing based both on biophysical conditions (water scarcity) and ethical impli- cations (human right to food). Blue water grabs are appropriations of irrigation (i.e., blue) water in regions affect- ed by undernourishment and where agricultural production is constrained by blue water availability. We use this framework to provide a global assessment of the likelihood that LSLAs entail blue water grabbing.

The growing global demand for food, fibers, and biofuels and the consequently, increasing prices of agricultural products have made investments in agriculture a priority for some governments and corporations. Since 2008, about 50 million ha of arable land have been purchased or leased worldwide, with an alarming and unprecedented increase in the number of land negotiations. When land acquisitions occur disregarding the rights of former land users and the socio-environmental impacts of these investments, they are often termed “land grabs.” Not only do large-scale land acquisitions (LSLAs) entail the purchase of fertile land but also the appropriation of land-based resources, such as water, with potential effects on the local population and the environment. Recently, a number of studies and reports have documented the process of LSLAs, while the associated effects on land and water resource availability to local communities have remained poorly investigated. Here, we develop an in-depth analysis of each land deal from the standpoint of land fertility, water scarcity, distance from roads, rivers, and villages. We focus on the case of Mozambique, a country affected by intense large-scale land acquisition, malnourishment, and demographic growth. Results show that, presently, LSLA in Mozambique covers an area of about 2 million hectares that account for roughly 30% of the currently cultivated land. Water resources appropriated through LSLAs are estimated around 39 billion m3 y−1, including 31 billion m3 y−1 for rainfed agriculture (green water) and a potential use of 8 billion m3 y−1 of water for irrigation (blue water), which corresponds to about 8 times the blue water currently used for agriculture across the country. The majority of land deals (29 out of 51) target fertile land and/or land with easy access to water resources and infrastructures.

Author(s): Rosa, L; Rulli, MC; Davis, KF; D'Odorico, P | Abstract: Shale deposits are globally abundant and widespread. Extraction of shale oil and shale gas is generally performed through water-intensive hydraulic fracturing. Despite recent work on its environmental impacts, it remains unclear where and to what extent shale resource extraction could compete with other water needs. Here we consider the global distribution of known shale deposits suitable for oil and gas extraction and develop a water balance model to quantify their impacts on local water availability for other human uses and ecosystem functions. We find that 31–44% of the world's shale deposits are located in areas where water stress would either emerge or be exacerbated as a result of shale oil or gas extraction; 20% of shale deposits are in areas affected by groundwater depletion and 30% in irrigated land. In these regions shale oil and shale gas production would likely compete for local water resources with agriculture, environmental flows, and other water needs. By adopting a hydrologic perspective that considers water availability and demand together, decision makers and local communities can better understand the water and food security implications of shale resource development.

Le Temps de l'Histoire; International audience; La Méditerranée des villes est déclinée dans une perspective braudélienne et une approche sociologique. Villes comme nœuds de communication de routes maritimes, depuis les villes portuaires du Nil et l’île-cité de Patmos jusqu’aux brillantes capitales, Constantinople ou Damas, ou de moins illustres comme Savone ou Smyrne qui eurent pourtant leur heure de gloire. D’autres villes, comme Tlemcen et Bône, se caractérisent par une sédimentation mémorielle, depuis l’Antiquité en passant par la medina médiévale jusqu’à l’époque coloniale qui bouleversa leur configuration. Avec les villes de la Méditerranée sont appréhendés leur histoire spécifique, l’ancrage du pouvoir et l’extension de leur territoire. Telle la ville-port de Gênes marquée par des emprises successives sur l’espace, mais aussi Grasse avec ses tours ou encore les villes d’Italie centrale avec le palais des seigneurs et les domus familiales. Marseille se situe dans la confrontation entre la commune et l’autorité royale : elle se veut autonome, parfois indépendante et insoumise. Rome passe d’une capitale à éclipse à une grande capitale où la centralisation, la renovatio urbis et les migrations transforment la société et le visage des quartiers périphériques. Apparaissent alors les communautés urbaines, leur vivre ensemble et leur identité. C’est l’histoire en devenir des communautés religieuses de Ciutat de Majorque. C’est le regard des nomades du Maghreb sur les villes. Ce sont les espaces de sociabilité dans les villes chypriotes. Enfin, la communauté politique peut s’écrire et perdurer, comme la Chronique de Montpellier, jusqu’à ce que guerres de religion et guerre civile brisent ce qui en faisait le ciment et la mémoire. [Sources : éditeur]

Vegetation and soils take up 20% of global anthropogenic greenhouse gas emission (1), and vegetation also plays an active role in regulating global water cycle (2). In PNAS, Branch and Wulfmeyer (3) conduct a detailed regional-scale simulation to show that agroforestry can significantly enhance rainfall in some desert regions and therefore could provide an effective biological engineering approach to sequestrate carbon (3). They also identify arid zones that have potential for desert agroforestry to enhance rainfall. The zones are mostly outside of the proposed areas available for potential tree restoration in a recent global analysis (4). This is an important finding. However, we argue that the conclusion misses an important piece of the puzzle: a comparison between … [↵][1]1To whom correspondence may be addressed. Email: lxwang{at}iupui.edu. [1]: #xref-corresp-1-1

In many tropical forests, where phosphorus (P) is considered a limiting nutrient, atmospheric deposition can contribute significantly to available P. Previous studies have shown that P inputs from atmospheric deposition are enhanced by plant canopies. This effect is explained as the result of increased deposition of P-rich aerosol particles (dry deposition) and fog droplets (fog or “occult” deposition) onto leaf surfaces. Here we studied the importance of fog as a source of P to a P-limited dry tropical forest. Throughout an 80 day period during the dry season when fog is most common, we sampled fog water and bulk precipitation in a clearing and measured leaf wetness and throughfall in an adjacent secondary and mature forest stand. During the study period, total P (PT) concentrations in fog water ranged from 0.15 to 6.40 mg/L, on average fourteenfold greater than PT concentrations in bulk precipitation (0.011 to 0.451 mg/L), and sixfold and sevenfold greater than throughfall PT concentrations in the secondary and mature forest stands, respectively (0.007 to 1.319 mg/L; 0.009 to 0.443 mg/L). Based on leaf area index, the frequency of fog deposition, and amount of water deposited per fog event, we estimate that fog delivers a maximum of 1.01 kg/ha/yr to secondary forest stands and 1.75 kg/ha/yr to mature forest stands, compared to 0.88 kg/ha/yr to secondary forest stands and 1.98 kg/ha/yr to mature forest stands via throughfall (wet + dry deposition) and stemflow. Thus, fog deposition may contribute substantially to available P in tropical dry forests.

Forests can affect environmental conditions in ways that enhance their survival. This effect may contribute to a positive feedback whereby deforestation could degrade environmental conditions and inhibit forest re-establishment. Sudden changes in forest functioning can be attributed to the existence of multiple stable states with one high and one low vegetation state. Multiple factors govern whether a transition between states will occur following deforestation. One such factor is strategic behavior and whether communities or stakeholders with an interest in the forest cooperate to maintain the forest in the fully vegetated state by reducing extraction levels or choose their own extraction rates without considering the collective effect of this behavior. We examine how the effect of a positive feedback and strategic behavior affect the optimal quantity of vegetation, V*. A clear hysteresis exists for logged forests exhibiting a positive feedback whereby an increase in extraction rates leads to a shift to the low vegetation state. An increase in the ecological value of the forest increases V* whereas the opposite is true for an increase in the value of timber. V* is also higher under cooperative conditions than non-cooperative conditions. Notably, accounting for the effect of a positive feedback substantially increases V*.

Drought persistence in West African Sahel has often been explained as an effect of positive vegetation-atmosphere feedback associated with surface albedo or the partitioning of solar radiation into sensible and latent heat fluxes. An often overlooked aspect of land-atmosphere coupling results from vegetation controls on dust emissions and the ability of mineral aerosols to suppress precipitation. Here we first consider the case of local (endogenous) dynamics within the Sahel, whereby enhanced dust emissions resulting from a decrease in vegetation partly suppress precipitation, thereby further reducing vegetation cover. We then account for teleconnections between Sahel precipitation and exogenous (i.e., Saharan) dust emissions due to an increase in Saharan wind speed in years of above average Sahel precipitation. We find that in both cases vegetation-climate dynamics may have two stable states, one with low precipitation and high concentration of atmospheric dust and the other with high precipitation and lower levels of atmospheric dust.

The escalating food demand by a growing and increasingly affluent global population is placing unprecedented pressure on the limited land and water resources of the planet, underpinning concerns over global food security and its sensitivity to shocks arising from environmental fluctuations, trade policies, and market volatility. Here, we use country-specific demographic records along with food production and trade data for the past 25 y to evaluate the stability and reactivity of the relationship between population dynamics and food availability. We develop a framework for the assessment of the resilience and the reactivity of the coupled population-food system and suggest that over the past two decades both its sensitivity to external perturbations and susceptibility to instability have increased.

The coexistence of woody plants and grasses in savannas is determined by a complex set of interacting factors that determine access to resources and demographic dynamics, under the control of external drivers and vegetation feedbacks with the physical environment. Existing theories explain coexistence mainly as an effect of competitive relations and/or disturbances. However, theoretical studies on the way facilitative interactions resulting from hydraulic lift affect tree-grass coexistence and the range of environmental conditions in which savannas are stable are still lacking. We investigated the role of hydraulic lift in the stability of tree-grass coexistence in savannas. To that end, we developed a new mechanistic model that accounts for both competition for soil water in the shallow soil and fire-induced disturbance. We found that hydraulic lift favors grasses, which scavenge the water lifted by woody plants. Thus, hydraulic lift expands (at the expenses of woodlands) the range of environmental conditions in which savannas are stable. These results indicate that hydraulic lift can be an important mechanism responsible for the coexistence of woody plants and grasses in savannas. Grass facilitation by trees through the process of hydraulic lift could allow savannas to persist stably in mesic regions that would otherwise exhibit a forest cover.

The soluble iron content and dust emission potential of sediment samples collected from the Taylor Valley in the McMurdo Dry Valleys (MDVs) and sea ice in the McMurdo Sound were evaluated to determine whether inputs to the Southern Ocean may be sufficient to affect ocean productivity. Our results show that the dust-generating potential from the MDVs soils are comparable to those of sediments from other major dust sources in the Southern Hemisphere. Sediments from the MDVs and sea ice are one order of magnitude richer in soluble iron than those in other dust sources in the Southern Hemisphere. Forward trajectory analyses show that the dust from the MDVs is likely to be deposited in the Southern Ocean. These results provide evidence of the possible supply of soluble iron to the Southern Ocean associated with dust transport from the MDVs, should climate change expand the exposed areas of the continent.

Growing demand for agricultural commodities for food, fuel and other uses is expected to be met through an intensification of production on lands that are currently under cultivation. Intensification typically entails investments in modern technology — such as irrigation or fertilizers — and increases in cropping frequency in regions suitable for multiple growing seasons. Here we combine a process-based crop water model with maps of spatially interpolated yields for 14 major food crops to identify potential differences in food production and water use between current and optimized crop distributions. We find that the current distribution of crops around the world neither attains maximum production nor minimum water use. We identify possible alternative configurations of the agricultural landscape that, by reshaping the global distribution of crops within current rainfed and irrigated croplands based on total water consumption, would feed an additional 825 million people while reducing the consumptive use of rainwater and irrigation water by 14% and 12%, respectively. Such an optimization process does not entail a loss of crop diversity, cropland expansion or impacts on nutrient and feed availability. It also does not necessarily invoke massive investments in modern technology that in many regions would require a switch from smallholder farming to large-scale commercial agriculture with important impacts on rural livelihoods. The current distribution of crops around the world neither attains maximum production nor minimum water use, according to a crop water model and yield data. An optimized crop distribution could feed an additional 825 million people and substantially reduce water use.

Desert surfaces are typically stable and represent some of the longest-lived landforms on Earth. For surfaces devoid of vegetation, the evolution of a desert pavement of gravel and small stones protects the surface from erosion by wind and water and vegetation further protects the surface in arid and semi-arid rangelands. The susceptibility of the land surface to wind erosion is enhanced by mechanical damage to the desert pavement or vegetation losses resulting from fire or grazing. Despite the relatively rich literature on the effects of grazing and fire on plant community composition, land degradation, and the productivity of arid landscapes, little is known about the effects of moderate grazing or fire on the erodibility of soils in desert grasslands and shrublands. Here we investigate the effects of simulated moderate grazing, simulated livestock trampling, and of fire on the resulting wind erodibility and dust emissions of the affected soil surfaces. We surveyed 24 plots of the same size, 6m×0.6m, at a research site in the northern Chihuahuan Desert including 6 plots in a shrub-grass ecotone, 12 plots in an adjacent grassland, and 6 plots in an area that had been burned by a natural wildfire 6months earlier but had no vegetation recovery due to the time of year and drought. To evaluate the various effects of disturbances on the susceptibility of the surface to wind erosion and dust entrainment, replicates of three plots underwent different treatments including clipping, trampling, fire, and tillage. We subsequently tested each of the treated plots with a portable field wind tunnel run at 12.6ms−1. We found that moderate grazing and fire did not result in great soil loss in desert grasslands but that shrublands were more seriously affected by grazing and fire. Total removal of vegetation and disturbance of the soil surface did result in greater than order of magnitude increases of vertical sediment flux and greater than three-fold increases of dust emissions.

Tropical forests are undergoing land use change in many regions of the world, including the African continent. Human populations living close to forest margins fragmented and disturbed by deforestation may be particularly exposed to zoonotic infections because of the higher likelihood for humans to be in contact with disease reservoirs. Quantitative analysis of the nexus between deforestation and the emergence of Ebola virus disease (EVD), however, is still missing. Here we use land cover change data in conjunction with EVD outbreak records to investigate the association between recent (2004–2014) outbreaks in West and Central Africa, and patterns of land use change in the region. We show how in these EVD outbreaks the index cases in humans (i.e. spillover from wildlife reservoirs) occurred mostly in hotspots of forest fragmentation.

© 2017 IOP Publishing Ltd. Ensuring food security requires food production and distribution systems function throughout disruptions. Understanding the factors that contribute to the global food system's ability to respond and adapt to such disruptions (i.e. resilience) is critical for understanding the long-term sustainability of human populations. Variable impacts of production shocks on food supply between countries indicate a need for national-scale resilience indicators that can provide global comparisons. However, methods for tracking changes in resilience have had limited application to food systems. We developed an indicator-based analysis of food systems resilience for the years 1992-2011. Our approach is based on three dimensions of resilience: socio-economic access to food in terms of income of the poorest quintile relative to food prices, biophysical capacity to intensify or extensify food production, and the magnitude and diversity of current domestic food production. The socio-economic indicator has a large variability, but with low values concentrated in Africa and Asia. The biophysical capacity indicator is highest in Africa and Eastern Europe, in part because of a high potential for extensification of cropland and for yield gap closure in cultivated areas. However, the biophysical capacity indicator has declined globally in recent years. The production diversity indicator has increased slightly, with a relatively even geographic distribution. Few countries had exclusively high or low values for all indicators. Collectively, these results are the basis for global comparisons of resilience between countries, and provide necessary context for developing generalizations about resilience in the global food system.

© 2016 Elsevier Ltd Agricultural intensification is often seen as a suitable approach to meet the growing demand for agricultural products and improve food security. It typically entails the use of fertilizers, new cultivars, irrigation, and other modern technology. In regions of the world affected by seasonal or chronic water scarcity, yield gap closure is strongly dependent on irrigation (blue water). Global yield gap assessments have often ignored whether the water required to close the yield gap is locally available. Here we perform a gridded global analysis (10 km resolution) of the blue water consumption that is needed annually to close the yield gap worldwide and evaluate the associated pressure on renewable freshwater resources. We find that, to close the yield gap, human appropriation of freshwater resources for irrigation would have to increase at least by 146%. Most study countries would experience at least a doubling in blue water requirement, with 71% of the additional blue water being required by only four crops – maize, rice, soybeans, and wheat. Further, in some countries (e.g., Algeria, Morocco, Syria, Tunisia, and Yemen) the total volume of blue water required for yield gap closure would exceed sustainable levels of freshwater consumption (i.e., 40% of total renewable surface and groundwater resources).

© 2017 The escalating human demand for food, water, energy, fibres and minerals have resulted in increasing commercial pressures on land and water resources, which are partly reflected by the recent increase in transnational land investments. Studies have shown that many of the land-water issues associated with land acquisitions are directly related to the areas of energy and food production. This paper explores the land-water-energy-food nexus in relation to large-scale farmland investments pursued by investors from European countries. The analysis is based on a “resource assessment approach” which evaluates the linkages between land acquisitions for agricultural (including both energy and food production) and forestry purposes, and the availability of land and water in the target countries. To that end, the water appropriated by agricultural and forestry productions is quantitatively assessed and its impact on water resource availability is analysed. The analysis is meant to provide useful information to investors from EU countries and policy makers on aspects of resource acquisition, scarcity, and access to promote responsible land investments in the target countries.

Rural populations around the world rely on small-scale farming and other uses of land and natural resources, which are often governed by customary, traditional, and indigenous systems of common property. In recent years, large-scale land acquisitions have drastically expanded; it is unclear whether the commons are a preferential target of these acquisitions. Here we argue that the contemporary global “land rush” could be happening at the expense of common-property systems around the world. While there is evidence that common-property systems have developed traditional institutions of resource governance that make them robust with respect to endogenous forces (e.g., uses by community members), it is less clear how vulnerable these arrangements are to exogenous drivers of globalization and expansion of transnational land investments. In common-property systems, farmers and local users may be unable to defend their customary rights and successfully compete with external actors. We define the notion of “commons grabbing” and report on an exploratory study that applied meta-analytical methods, drawing from the recent literature on large-scale land acquisitions and land grabbing. Informed by political economy and political ecology approaches, we coded selected cases on the basis of acquisition mechanisms, claims and property rights, changes in production system, and coercive dynamics, and explored the interactions between the different variables using association tests and qualitative comparative analysis. We found that the majority of the cases included in this analysis (44 of 56) could be examples of commons grabbing.

© 2017 by the authors. Demographic growth, changes in diet, and reliance on first-generation biofuels are increasing the human demand for agricultural products, thereby enhancing the human pressure on global freshwater resources. Recent research on the food-water nexus has highlighted how some major agricultural regions of the world lack the water resources required to sustain current growth trends in crop production. To meet the increasing need for agricultural commodities with limited water resources, the water use efficiency of the agricultural sector must be improved. In this regard, recent work indicates that the often overlooked strategy of changing the crop distribution within presently cultivated areas offers promise. Here we investigate the extent to which water in the United States could be saved while improving yields simply by replacing the existing crops with more suitable ones. We propose crop replacement criteria that achieve this goal while preserving crop diversity, economic value, nitrogen fixation, and food protein production. We find that in the United States, these criteria would greatly improve calorie (+46%) and protein (+34%) production and economic value (+208%), with 5% water savings with respect to the present crop distribution. Interestingly, greater water savings could be achieved in water-stressed agricultural regions of the US such as California (56% water savings), and other western states.

Ecological processes in arid lands are often described by the pulse-reserve paradigm, in which rain events drive biological activity until moisture is depleted, leaving a reserve. This paradigm is frequently applied to processes stimulated by one or a few precipitation events within a growing season. Here we expand the original framework in time and space and include other pulses that interact with rainfall. This new hierarchical pulse-dynamics framework integrates space and time through pulse-driven exchanges, interactions, transitions, and transfers that occur across individual to multiple pulses extending from micro to watershed scales. Climate change will likely alter the size, frequency, and intensity of precipitation pulses in the future, and arid-land ecosystems are known to be highly sensitive to climate variability. Thus, a more comprehensive understanding of arid-land pulse dynamics is needed to determine how these ecosystems will respond to, and be shaped by, increased climate variability.

The impacts of climate change on carbon (C) and nitrogen (N) fluxes are not fully understood, especially in savanna ecosystems. This study aimed to assess the potential impacts of climate change in soil C and N pools in the savannas. Soil organic carbon (SOC) and total nitrogen (TN) were quantified at four sites with consistent sandy soils along a precipitation gradient in the southern Africa savannas. Soils were sampled at 240 locations at each site at four depths: 10, 30, 70 and 120 cm. The driest site and the wettest site had the SOC content of 1,397 g m−2 and 1,982 g m−2, respectively. Mean C:N ratio was highest (26 ± 6) at the wettest site and lowest at the next-wettest (15 ± 2). Our results support the hypothesis of low nitrogen fixation in the area, particularly in the dry southern region. We found a significant spatial relationship between SOC/TN content and tree height or tree mass only in the driest. The Botswana Kalahari (BK) soil is estimated to contain about 0.99 × 1015 g C belowground of which about 92 % is SOC. Furthermore, under IPCC RCP4.5 and RCP8.5 carbon emission scenarios, total belowground C is predicted to drop to 0.92 and 0.86 × 1015 g C, respectively by the end of the century. Our results provide insight into soil C stocks in Kalahari savannas and suggest that savannas may be bigger stores of organic C than currently thought. The current climate change projections together with field measurements suggest that C storage in these savannas may decrease in the future as the region warms and dries into the next century.

The recent intensification of international trade has led to a globalization of food commodities and to an increased disconnection between human populations and the land and water resources that support them through crop and livestock production. Several countries are not self-sufficient and depend on imports from other regions. Despite the recognized importance of the role of trade in global and regional food security, the societal reliance on domestic production and international trade remains poorly quantified. Here we investigate the global patterns of food trade and evaluate the dependency of food security on imports. We investigate the relationship existing between the trade of food calories and the virtual transfer of water used for their production. We show how the amount of food calories traded in the international market has more than doubled between 1986 and 2009, while the number of links in the trade network has increased by more than 50%. Likewise, global food production has increased by more than 50% in the same period, providing an amount of food that is overall sufficient to support the global population at a rate of 2700–3000 kcal per person per day. About 23% of the food produced for human consumption is traded internationally. The water use efficiency of food trade (i.e., food calories produced per unit volume of water used) has declined in the last few decades. The water use efficiency of food production overall increases with the countries' affluence; this trend is likely due to the use of more advanced technology.

Hydraulic redistribution defined as the translocation of soil moisture by plant root systems in response to water potential gradients is a phenomenon widely documented in different climate, vegetation, and soil conditions. Past research has largely focused on hydraulic redistribution in deep tree roots with access to groundwater and/or winter rainfall, while the case of relatively shallow (i.e., ≈1–2 m deep) tree roots has remained poorly investigated. In fact, it is not clear how hydraulic redistribution in shallow root zones is affected by climate, vegetation, and soil properties. In this study, we developed a model to investigate the climate, vegetation, and soil controls on the net direction and magnitude of hydraulic redistribution in shallow tree root systems at the growing season to yearly timescale. We used the model to evaluate the effect of hydraulic redistribution on the water stress of trees and grasses. We found that hydraulic lift increases with decreasing rainfall frequency, depth of the rooting zone, root density in the deep soil and tree leaf area index; at the same time for a given rainfall frequency, hydraulic lift increases with increasing average rainstorm depth and soil hydraulic conductivity. We propose that water drainage into deeper soil layers can lead to the emergence of vertical water potential gradients sufficient to explain the occurrence of hydraulic lift in shallow tree roots without invoking the presence of a shallow water table or winter precipitation. We also found that hydraulic descent reduces the water stress of trees and hydraulic lift reduces the water stress of grass with important implications on tree–grass interactions.

Author(s): He, Y; D'Odorico, P; De Wekker, SFJ | Abstract: Many regions of the world are affected by a major land cover change resulting from the encroachment of woody plants and the conversion of grasslands into shrublands. In the southwestern United States, such a change in vegetation cover has been found to increase the winter nighttime temperature, thereby contributing to a positive feedback between shrub encroachment and microclimate in areas encroached by cold-sensitive shrubs. Temperature measurements show that winter minimum temperatures are on average ~2K higher in shrubland than in adjacent grassland sites. It is unclear how the nighttime warming induced by shrub encroachment compares with regional climate trends. We address this question by analysing both the historical and future regional temperature trends in central New Mexico. The estimated regional increase in minimum winter temperature ranges from 1 to 4K per century using observations and climate models. Thus, the warming resulting from shrub encroachment is equivalent to a change in regional climate over a time period of century scale, which suggests that shrub encroachment has an overall important effect on the regional climate.

During the past several decades, woody plants have been encroaching into grasslands around the world. This transition in plant dominance is often explained as a state shift in bistable ecosystem dynamics induced by fire-vegetation feedbacks. These feedbacks occur when woody plants are able to displace grasses because of their better access to soil water and light. On the other hand, grasses can displace woody plants because of their ability to increase fire frequency and of the higher susceptibility of woody plants to fire-induced mortality. In this study, we present an ecohydrological framework to investigate the displacement of grasses by woody plants. Considering the effect of lateral root spread and of soil water and light limitations, we found that woody plant encroachment can substantially suppress grass production even without the presence of grazers. Bistable dynamics emerge as a result of the grass-fire feedback for a wide range of rainfall conditions, fire susceptibility, and woody plant growth rates.

It is well documented that deforestation results in an increase in landslide frequency due to the control that forest roots have on slope stability. The loss of forest vegetation leads to a reduction in soil cohesion and a decrease in the shear strength of the soil profile. As a result, the slope becomes more susceptible to landsliding and the return time of landslides decreases. When a landslide removes the soil profile, there may not be adequate time for seedlings to grow and enhance soil stability. In this study, we investigate whether bistable dynamics emerge from the interaction of forest vegetation with the formation and accumulation of colluvial deposits in soil-mantled landscapes. To that end, we develop deterministic and stochastic models of landslide occurrence with a dynamic vegetation component. Results show that bistability exists for the deterministic case for both steep and shallow hollows under event and supply limited conditions. However, for the stochastic case, the randomness of landslide occurrence largely changed the states of the system such that the system only exhibited one stable state, which was the fully vegetated condition. Examining different management practices under stochastic conditions showed that the system eventually recovered; however, management practices influenced the recovery time of the forest. Thus, different management practices could render the land in a state of low vegetation over economically significant time periods.

Author(s): Rosa, Lorenzo; Chiarelli, Davide Danilo; Tu, Chengyi; Rulli, Maria Cristina; D'Odorico, Paolo | Abstract: Recent studies have highlighted the reliance of global food production on unsustainable irrigation practices, which deplete freshwater stocks and environmental flows, and consequently impair aquatic ecosystems. Unsustainable irrigation is driven by domestic and international demand for agricultural products. Research on the environmental consequences of trade has often concentrated on the global displacement of pollution and land use, while the effect of trade on water sustainability and the drying of over-depleted watercourses has seldom been recognized and quantified. Here we evaluate unsustainable irrigation water consumption (UWC) associated with global crop production and determine the share of UWC embedded in international trade. We find that, while about 52% of global irrigation is unsustainable, 15% of it is virtually exported, with an average 18% increase between year 2000 and 2015. About 60% of global virtual transfers of UWC are driven by exports of cotton, sugar cane, fruits, and vegetables. One third of UWC in Mexico, Spain, Turkmenistan, South Africa, Morocco, and Australia is associated with demand from the export markets. The globalization of water through trade contributes to running rivers dry, an environmental externality commonly overlooked by trade policies. By identifying the producing and consuming countries that are responsible for unsustainable irrigation embedded in virtual water trade, this study highlights trade links in which policies are needed to achieve sustainable water and food security goals in the coming decades.

Fire can induce long-lived changes to land-surface albedo, an important aspect of the Earth’s energy budget, but the temporal evolution of these anomalies is poorly understood. Due to the widespread presence of fire in Africa, this represents uncertainty in the continental energy budget, which has important implications for regional climate and hydrologic cycling. In this study, we present the first object-based accounting of albedo anomalies induced by larger (>1 km2) individual wildfires in sub-Saharan Africa. We group spatially contiguous wildfire pixels into fire objects and track the albedo anomaly for five years after the burn. We find that albedo anomalies all have the same general temporal signature: An immediate, brief period of darkening followed by persistent brightening. The strongest brightening is found in the Kalahari region while more intense and long-lived initial darkening is found in the Sahel region. The average southern hemisphere albedo anomaly is +1.50 × 10−3 in the year following wildfire, representing a statistically significant negative surface energy balance forcing on a continental scale. This study challenges an existing paradigm surrounding the physical effects of fire on the landscape. Our results suggest that models of albedo that assume a darkening and recovery to baseline are overly simplistic in almost all circumstances. Furthermore, the presumption that immediate darkening is the only meaningful effect on albedo is incorrect for the majority of the African continent.

The increasing global demand for farmland products is placing unprecedented pressure on the global agricultural system and its water resources. Many regions of the world, that are affected by a chronic water scarcity relative to their population, strongly depend on the import of agricultural commodities and associated embodied (or virtual) water. The globalization of water through virtual water trade (VWT) is leading to a displacement of water use and a disconnection between human populations and the water resources they rely on. Despite the recognized importance of these phenomena in reshaping the patterns of water dependence through teleconnections between consumers and producers, their effect on global and regional water resources has just started to be quantified. This review investigates the global spatiotemporal dynamics, drivers, and impacts of VWT through an integrated analysis of surface water, groundwater, and root-zone soil moisture consumption for agricultural production; it evaluates how virtual water flows compare to the major ‘physical water fluxes’ in the Earth System; and provides a new reconceptualization of the hydrologic cycle to account also for the role of water redistribution by the hidden ‘virtual water cycle’.

[1] The increasing global demand for food, fibers, and biofuels has made investments in agriculture a priority for some governments and corporations eager to expand their agricultural production while securing good profits. Here we calculate the water appropriation associated with land deals at different negotiation and implementation stages. Using estimates of actual and potential evapotranspiration for the crops planted in the acquired land, we calculate the green and blue water appropriated by land investors under a variety of irrigation scenarios. We also determine the grey water footprint as the amount of water required to dilute to allowable standards the pollution resulting from fertilizer applications. We found that about 380 × 109 m3 yr−1 of rainwater is appropriated with the 43 million ha of reported contract area acquired by agri-investors (>240 × 109 m3 yr−1 in the 29 million ha of foreign acquisitions only). This water would be sufficient to feed ≈ 300–390 million people.

[1] For some phosphorus (P)-limited ecosystems, vegetation can be sustained by atmospheric P inputs. The ability of the canopy to trap airborne particles influences atmospheric P deposition. This dependence suggests a positive feedback, which could impact forest regeneration following deforestation. We examine how the amount of P deposited atmospherically varies as a function of forest canopy characteristics. We quantify the amount of P in bulk deposition (i.e., rainfall and dry deposition) and throughfall from a mature forest and 6 year old successional vegetation stand. To rule out the possibility that P enrichment in throughfall is due to canopy leaching, we construct an artificial forest made of P-free plastic materials. We then compare throughfall samples collected beneath the artificial forest with those collected beneath the successional vegetation due to similarities in forest characteristics such as height and stem density. Over 1 year, 0.6 ± 0.1 kg P ha−1 yr−1 were deposited in the open area, 0.8 ± 0.0 kg P ha−1 yr−1 beneath the successional vegetation, 0.5 ± 0.0 kg P ha−1 yr−1 beneath the artificial forest, and 1.9 ± 0.0 kg P ha−1 yr−1 beneath the mature forest. Results also showed an enrichment of P concentration beneath the artificial forest relative to the open area. Atmospheric P sources sustain 37% of the annual P demand in the mature forest, but only 13% in the successional vegetation. Thus, following deforestation, more of the P demand would have to be met from other sources that if unavailable, could lead to conditions where the forest does not recover.

Savannah ecosystems are important carbon stocks on the Earth, and their quantification is crucial for understanding the global impact of climate and land-use changes in savannahs. The estimation of aboveground/belowground plant biomass requires tested allometric relationships that can be used to determine total plant biomass as a function of easy-to-measure morphological indicators. Despite recent advances in savannah ecology, research on allometric relations in savannahs remains confined to a few site-specific studies where basal area is typically used as the main morphometric parameter with plant biomass. We investigate allometric relations at four sites along a 950-km transect in the Kalahari across mean rainfall gradient 170 mm yr-1-550 mm yr-1. Using data from 342 harvested trees/shrubs, we relate basal area, height and crown diameter to aboveground biomass. These relationships are strongest in trees and weakest in small shrubs. Strong allometric relationships are also determined for morphologically similar groups of woody vegetation. We show that crown diameter can be used as an alternative to basal area in allometric relationships with plant biomass. This finding may enhance the ability to determine aboveground biomass over large areas using high-resolution aerial or satellite imagery without requiring ground-based measurements of basal area. © 2013 John Wiley & Sons Ltd.

[1] The Southern Hemisphere shows relatively low levels of atmospheric dust concentrations. Dust concentrations could, however, increase as a result of losses of vegetation cover in the southern Kalahari. There is some evidence of an ongoing remobilization of stabilized dunefields in the southern Kalahari where dune crests with sparse vegetation cover are reactivated during dry and windy periods, a phenomenon that is predicted to intensify with increased land degradation, overgrazing, and droughts. Despite the potentially important climatic and biogeochemical implications of dust emissions from the Kalahari, it is still unclear whether the predicted remobilization of the Kalahari dunes could be associated with increased dust emissions from this region. The dependence of sediment fluxes and dust emissions on vegetation cover in the Kalahari dunelands remains poorly understood, which prevents a quantitative assessment of possible changes in aeolian activity in this region under different land use and land cover scenarios. In this study, we report the results of an aeolian sediment sampling campaign over a variety of land covers in the southern Kalahari. We use these results to quantify the potential rate of dust emissions and its dependence on vegetation cover and to make an estimate of dust fluxes from a portion of the southern Kalahari. The results show that the loss of vegetation could lead to substantial increases in dust emission and nutrient loss.

Phosphorus (P) availability in soils can be a major factor limiting vegetation growth. Vegetation has adapted to this limitation by efficiently cycling P. Under conditions of limited P, microbes aid in mitigating P losses and enhancing P availability. Deforestation adversely impacts microbial populations. In turn, the loss of microbial biomass increases P losses and decreases P availability. This is important because P is not replenished biologically. Hence, when lost from the system, P only becomes available for uptake over geologic time scales. While vegetation clearly affects the microbial community and P cycling, it is not well-understood whether a loss of vegetation could lead to state changes in the vegetation dynamics. We develop a modeling framework and apply it to a P-limited cerrado ecosystem in Brazil with high intra-annual rainfall variability to examine whether deforestation can lead to a shift to a stable tree-less state. Following deforestation, we observed a decline in the microbial pool, a reduction in immobilization, and an increase in P losses. Although vegetation recovered from deforestation, a significant decline in the recalcitrant organic P pool occurred. A larger reduction in this pool led to a state change to the bare state from which the vegetation and microbial biomass did not recover. Results suggest that systems most susceptible to state changes may be those which have been previously deforested or those where the amount of P stored in the recalcitrant organic pool is low or becomes available very slowly.

Societal pressure on the global land and freshwater resources is increasing as a result of the rising food demand by the growing human population, dietary changes, and the enhancement of biofuel production induced by the rising oil prices and recent changes in United States and European Union bioethanol policies. Many countries and corporations have started to acquire relatively inexpensive and productive agricultural land located in foreign countries, as evidenced by the dramatic increase in the number of transnational land deals between 2005 and 2009. Often known as “land grabbing,” this phenomenon is associated with an appropriation of freshwater resources that has never been assessed before. Here we gather land-grabbing data from multiple sources and use a hydrological model to determine the associated rates of freshwater grabbing. We find that land and water grabbing are occurring at alarming rates in all continents except Antarctica. The per capita volume of grabbed water often exceeds the water requirements for a balanced diet and would be sufficient to improve food security and abate malnourishment in the grabbed countries. It is found that about 0.31 × 10 12 m 3 ⋅y −1 of green water (i.e., rainwater) and up to 0.14 × 10 12 m 3 ⋅y −1 of blue water (i.e., irrigation water) are appropriated globally for crop and livestock production in 47 × 10 6 ha of grabbed land worldwide (i.e., in 90% of the reported global grabbed land).