Spatial pattern formation induced by Gaussian white noise

The ability of Gaussian noise to induce ordered states in dynamical systems is here presented in an overview of the main stochastic mechanisms able to generate spatial patterns. These mechanisms involve: (i) a deterministic local dynamics term, accounting for the local rate of variation of the field variable, (ii) a noise component (additive or multiplicative) accounting for the unavoidable environmental disturbances, and (iii) a linear spatial coupling component, which provides spatial coherence and takes into account diffusion mechanisms. We investigate these dynamics using analytical tools, such as mean-field theory, linear stability analysis and structure function analysis, and use numerical simulations to confirm these analytical results.Comment: 11 pages, 8 figure

Early warning signs in social-ecological networks

Social ecological systems are often difficult to investigate and manage because of their inherent complexity1. Small variations in external drivers can lead to abrupt changes associated with instabilities and bifurcations in the underlying dynamics2-4. Anticipating critical transitions and divergence from the present state of the system is particularly crucial to the prevention or mitigation of the effects of unwanted and irreversible changes5-10. Recent research in ecology has focused on leading indicators of regime shift in ecosystems characterized by one state variable5,7,11,12. The case of systems with several mutually interacting components, however, has remained poorly investigated13, while the connection between network stability and research on indicators for loss of resilience has been elusive14. Here we develop a theoretical framework to analyze early warning signs of instability and regime shift in social ecological networks. We provide analytical expressions for a set of precursors of instability in social ecological systems with additive noise for a variety of network structures. In particular, we show that the covariance matrix of the dynamics can effectively anticipate the emergence of instability. We also compare signals of early warning based on the dynamics of suitably selected nodes, to indicators based on the integrated behavior of the whole network. We find that the performances of these indicators are affected by the network structure and the type of interaction among nodes. These results provide new advances in multidimensional early warning analysis and offer a framework to evaluate the resilience of social ecological networks.Comment: 14 pages, 4 figures. Supplementary Information available upon reques

Weak and Strong Sustainability of Irrigation: A Framework for Irrigation Practices Under Limited Water Availability

Agriculture strongly relies on irrigation. While irrigated land accounts for roughly 20% of the global cultivated area, it contributes to about 40% of crop production. In the last few decades, the growing demand for agricultural commodities has translated into an increasing pressure on the global freshwater resources, often leading to their unsustainable use. Here we investigate the sustainability of irrigation, balancing farmers' profit generation objectives and the needs of ecological systems. We ask the question "sustainability of what?", to stress how the sustainability of irrigation is often evaluated with respect the opposing needs of humans and nature. While from the farmers' perspective irrigation is sustainable when it provides uninterrupted access to water resources at a price not exceeding the marginal revenue they generate (clearly without accounting for environmental externalities), from the standpoint of water resources, irrigation is sustainable if it does not deplete freshwater stocks or environmental flows. We invoke the notions of 'weak' and 'strong' sustainability to develop a novel framework for the evaluation of tradeoffs between human needs and the conservation of natural capital. Through the analysis of criteria of performance, we relate water deficit and irrigation overuse to the reliability and resilience of irrigation. This approach is applied to the case of Australia, a major agricultural country affected by water scarcity. The application of the framework to the case of Australia shows how this approach can be used to highlight areas in which irrigation contributes to a weakly sustainable use of water resources with impacts on environmental flows and groundwater stocks. Solutions, such as increasing efficiencies or reducing water applications through the adoption of deficit irrigation, can enhance water sustainability in some water scarce locations

The global land rush and climate change

Climate change poses a serious global challenge in the face of rapidly increasing human demand for energy and food. A recent phenomenon in which climate change may play an important role is the acquisition of large tracts of land in the developing world by governments and corporations. In the target countries, where land is relatively inexpensive, the potential to increase crop yields is generally high and property rights are often poorly defined. By acquiring land, investors can realize large profits and countries can substantially alter the land and water resources under their control, thereby changing their outlook for meeting future demand. While the drivers, actors, and impacts involved with land deals have received substantial attention in the literature, we propose that climate change plays an important yet underappreciated role, both through its direct effects on agricultural production and through its influence on mitigative or adaptive policy decisions. Drawing from various literature sources as well as a new global database on reported land deals, we trace the evolution of the global land rush and highlight prominent examples in which the role of climate change is evident. We find that climate change—both historical and anticipated—interacts substantially with drivers of land acquisitions, having important implications for the resilience of communities in targeted areas. As a result of this synthesis, we ultimately contend that considerations of climate change should be integrated into future policy decisions relating to the large-scale land acquisitions

The interactive nutrient and water effects on vegetation biomass at two African savanna sites with different mean annual precipitation

Author's manuscript made available in accordance with the publisher's policy.Savannahs cover more than 40% of Africa and provide a variety of important ecosystem services. Their productivity is constrained by disturbance and limiting resources. In southern Africa, fine-leaf savannahs typical of arid environments are known for being richer in nutrients than broad-leaf mesic savannahs. However, despite numerous recent studies on the dynamics of southern African savannahs, the interplay between water and nutrient limitations remains poorly investigated in these systems. To better understand the interactions between water, nutrients (N and P in this manuscript) and grazing on the productivity of grasses and trees in fine-leaf savannah ecosystems, a fertilization experiment with controlled grazing was conducted at two sites with different mean annual rainfall in Namibia. The experiment demonstrated that the vegetation at the drier site may not be nutrient-limited (N, P or N + P). At the wetter site, however, vegetation showed significant response to nutrient addition. Grasses exhibited N limitation and trees exhibited P limitation. This experiment also showed that grazing reduces the overall grass biomass, but may not modify the response to nutrient treatments. The results indicated a switch from water to nutrient limitation between dry and wet sites and demonstrated different tree and grass responses to nutrient additions

To what extent can agriculture be reshaped to address healthy and sustainable diets by boosting pulse production locally?

The consumption of unhealthy and environmentally unsustainable diets is a major societal challenge because of its impacts on human health and the environment. The adoption of micronutrient-rich diets with relatively low pressure on natural resources is an important development target at the intersection between sustainability and public health goals. Pulses are known for being rich in proteins and micronutrients, while having several environmental benefits. It is still unclear to what extent improving the nutritional content of diets by boosting pulse consumption can address health concerns associated with micronutrient deficiency without exacerbating environmental impacts. Here we evaluate to what extent environmentally sustainable, healthy diets can be achieved by increasing pulse production, while reducing the areas cultivated with cereals. To that end, taking as case studies two low/middle income countries (i.e., Pakistan and Nigeria) with high prevalence of nutritional diseases among children and women, we study different crop replacement scenarios that can boost pulse supply and comply with the micronutrient requirements suggested by the EAT-Lancet Commission. We find that in Nigeria the recommended pulse intake requirement can be met by increasing the domestic production of pulses, while saving 27% of water consumption. Conversely, in Pakistan the recommended levels of pulse intake are barely met because of the limited area suitable for pulse production. Overall, the current low yields of pulses and the limited availability of land suitable for pulse production are the main constraints to their supply in these two countries