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Covering around 41% of Earth’s surface and supporting more than one-third of human livelihoods, dryland ecosystems are unquestionably important. Considering that these regions foster many livelihoods that are vulnerable due to poverty and food insecurity (issues that should be exacerbated by climate change), understanding changes in dryland ecosystems and their drivers becomes even more important. Changes in dryland ecosystem functioning can take place gradually or abruptly (the so-called turning points, or TP). Better understanding where and how TPs occur, what causes them, and whether or not they can be predicted could support nature conservation and food security in drylands. With that in mind, first we detected where and when TPs in dryland ecosystem functioning mostly occurred, and characterizing them based on the direction and rate of change before/after the TP. This was done by using time series (1982-2015) of vegetation productivity and precipitation data in global drylands. Hotspot regions with high TP occurrence were detected in North America, the Sahel, Central Asia, and Australia. Next, we focused on better understanding the drivers of abrupt changes and ecosystem productivity in drylands, by (i) studying a drought-induced woody plants die-off case that occurred in Senegal in 2014-2015 and (ii) assessing the anthropogenic footprint over drylands. Although anthropogenic pressure did not present a significant impact over the die-off severity and post-disturbance recovery, soil physical characteristics showed to be important for both. The anthropogenic footprint assessment showed that from 1982 to 2015 there was a decrease in over-productive dryland areas due to human activity, while under-productive areas increased. Finally, the predictability of TPs was evaluated in the Sahel. We demonstrated the usefulness of using changes in ecosystems' resilience as an early warning indicator of abrupt changes, and also showed that human activity might hamper the use of such an early warning signal. We hope that our findings can support decision making and a correct allocation of resources, e.g., by supporting policymakers in the decision of whether or not intervention is needed, by helping in determining the necessary measures to be implemented, and by supporting in the delimitation of priority areas for conservation and/or management.
Drylands cover 41 percent of the earth' s terrestrial surface. The urgency of and international response to climate change have given a new place to drylands in terms both of their vulnerability to predicted climate change impacts and their potential contribution to climate change mitigation. This book aims to apply the new scientific insights on complex dryland systems to practical options for development. A new dryland paradigm is built on the resources and capacities of dryland peoples, on new and emergent economic opportunities, on inward investment, and on the best support that dryland science can offer.
Biological soil crusts (biocrusts) are widely distributed throughout the world, and cover approximately 12% of the terrestrial surface. Biocrusts are composed of cyanobacteria, algae, lichens, mosses, and a great diversity of other microorganisms, which bind soil particles together to form a layer of biological-soil matrix on the soil surface typically of several millimetres thickness. They are important sites of regional and global microbial diversity and perform multiple ecological functions (multifunctionality). During the evolution of terrestrial life on earth, biocrusts are regarded as the main colonising photosynthetic organisms before the advent of vascular vegetation. They not only represent the early stages of terrestrial ecosystems, but also facilitate the ecosystem’s development and succession. Therefore, biocrusts are recognised as ecological engineers in the natural development of ecosystems and for the restoration of degraded terrestrial ecosystems. The development of biocrusts is highly heterogeneous, which is reflected on both temporal and spatial scales, and this heterogeneity is still clearly visible even in a small scale. However, up to now, only limited knowledge is acquired on biocrust temporal and spatial organisation. In particular there still is a large knowledge gap regarding the various biocrust communities under different developmental states and their related physiological metabolisms and ecological functions. Therefore, in-depth studies of these issues will undoubtedly further promote our understanding of the heterogeneous development of biocrusts, as well as their ecological multifunctionality in terrestrial ecosystems. The relevant contributions are expected to provide a scientific basis for the management of biocrusts and technology development (e.g. cyanobacteria-induced biocrust technology) for ecological restoration and the promotion of soil health.
1. Terrestrial vegetation influences hydrologic cycling. In water-limited, dryland ecosystems, altered ecohydrology as a consequence of vegetation change can impact vegetation structure, ecological functioning and ecosystem services. Shrub steppe ecosystems dominated by big sagebrush (Artemisia tridentata) are widespread across western North America, and provide a range of ecosystem services. While sagebrush abundance in these ecosystems has been altered over the past century, and changes are likely to continue, the ecohydrological consequences of sagebrush removal and reestablishment remain unclear. 2. To characterize the immediate and medium-term patterns of water cycling and availability following sagebrush plant community alteration, we applied the SOILWAT ecosystem water balance model to 898 sites across the distribution of sagebrush ecosystems, representing the three primary sagebrush ecosystem types: sagebrush shrublands, sagebrush steppe and montane sagebrush. At each site, we examined three vegetation conditions representing intact sagebrush, recently disturbed sagebrush and recovered but grass-dominated vegetation. 3. Transition from shrub to grass dominance decreased precipitation interception and transpiration and increased soil evaporation and deep drainage. Relative to intact sagebrush vegetation, simulated soils in the herbaceous vegetation phases typically had drier surface layers and wetter deep layers. 4. Our simulations suggested that alterations in ecosystem water balance may be most pronounced in vegetation representing recently disturbed conditions (herbaceous vegetation with low biomass) and only modest in conditions representing recovered, but still grass-dominated vegetation. Furthermore, the ecohydrological impact of simulated sagebrush removal depended on climate; while short-term changes in water balance were greatest in wet areas represented by the montane sagebrush ecosystem type, medium-term impacts were greatest in dry areas of sagebrush shrublands and sagebrush steppe. 5. Synthesis. This study provides a novel, regional-scale assessment of how plant functional type transitions may impact ecosystem water balance in sagebrush-dominated ecosystems of North America. Results illustrate that the ecohydrological consequences of changing vegetation depend strongly on climate and suggest that decreasing woody plant abundance may have only limited impact on evapotranspiration and water yield.
Ecosystems and Human Well-Being is the first product of the Millennium Ecosystem Assessment, a four-year international work program designed to meet the needs of decisionmakers for scientific information on the links between ecosystem change and human well-being. The book offers an overview of the project, describing the conceptual framework that is being used, defining its scope, and providing a baseline of understanding that all participants need to move forward. The Millennium Assessment focuses on how humans have altered ecosystems, and how changes in ecosystem services have affected human well-being, how ecosystem changes may affect people in future decades, and what types of responses can be adopted at local, national, or global scales to improve ecosystem management and thereby contribute to human well-being and poverty alleviation. The program was launched by United National Secretary-General Kofi Annan in June 2001, and the primary assessment reports will be released by Island Press in 2005. Leading scientists from more than 100 nations are conducting the assessment, which can aid countries, regions, or companies by: providing a clear, scientific picture of the current sta
The pronounced constraints on ecosystem functioning and human livelihoods in drylands are frequently exacerbated by natural and socio-economic stresses, including weather extremes and inequitable trade conditions. Therefore, a better understanding of the relation between these stresses and the socio-ecological systems is important for advancing dryland development. The concept of vulnerability as applied in this dissertation describes this relation as encompassing the exposure to climate, market and other stresses as well as the sensitivity of the systems to these stresses and their capacity to adapt. With regard to the interest in improving environmental and living conditions in drylands, this dissertation aims at a meaningful generalisation of heterogeneous vulnerability situations. A pattern recognition approach based on clustering revealed typical vulnerability-creating mechanisms at global and local scales. One study presents the first analysis of dryland vulnerability with global coverage at a sub-national resolution. The cluster analysis resulted in seven typical patterns of vulnerability according to quantitative indication of poverty, water stress, soil degradation, natural agro-constraints and isolation. Independent case studies served to validate the identified patterns and to prove the transferability of vulnerability-reducing approaches. Due to their worldwide coverage, the global results allow the evaluation of a specific system's vulnerability in its wider context, even in poorly-documented areas. Moreover, climate vulnerability of smallholders was investigated with regard to their food security in the Peruvian Altiplano. Four typical groups of households were identified in this local dryland context using indicators for harvest failure risk, agricultural resources, education and non-agricultural income. An elaborate validation relying on independently acquired information demonstrated the clear correlation between weather-related damages and the identified clusters. It also showed that household-specific causes of vulnerability were consistent with the mechanisms implied by the corresponding patterns. The synthesis of the local study provides valuable insights into the tailoring of interventions that reflect the heterogeneity within the social group of smallholders. The conditions necessary to identify typical vulnerability patterns were summarised in five methodological steps. They aim to motivate and to facilitate the application of the selected pattern recognition approach in future vulnerability analyses. The five steps outline the elicitation of relevant cause-effect hypotheses and the quantitative indication of mechanisms as well as an evaluation of robustness, a validation and a ranking of the identified patterns. The precise definition of the hypotheses is essential to appropriately quantify the basic processes as well as to consistently interpret, validate and rank the clusters. In particular, the five steps reflect scale-dependent opportunities, such as the outcome-oriented aspect of validation in the local study. Furthermore, the clusters identified in Northeast Brazil were assessed in the light of important endogenous processes in the smallholder systems which dominate this region. In order to capture these processes, a qualitative dynamic model was developed using generalised rules of labour allocation, yield extraction, budget constitution and the dynamics of natural and technological resources. The model resulted in a cyclic trajectory encompassing four states with differing degree of criticality. The joint assessment revealed aggravating conditions in major parts of the study region due to the overuse of natural resources and the potential for impoverishment. The changes in vulnerability-creating mechanisms identified in Northeast Brazil are well-suited to informing local adjustments to large-scale intervention programmes, such as "Avança Brasil". Overall, the categorisation of a limited number of typical patterns and dynamics presents an efficient approach to improving our understanding of dryland vulnerability. Appropriate decision-making for sustainable dryland development through vulnerability reduction can be significantly enhanced by pattern-specific entry points combined with insights into changing hotspots of vulnerability and the transferability of successful adaptation strategies.
This volume summarizes our current understanding of biological soil crusts (biocrusts), which are omnipresent in dryland regions. Since they cover the soil surface, they influence, or even control, all surface exchange processes. Being one of the oldest terrestrial communities, biocrusts comprise a high diversity of cyanobacteria, algae, lichens and bryophytes together with uncounted bacteria, and fungi. The authors show that biocrusts are an integral part of dryland ecosystems, stabilizing soils, influencing plant germination and growth, and playing a key role in carbon, nitrogen and water cycling. Initial attempts have been made to use biocrusts as models in ecological theory. On the other hand, biocrusts are endangered by local disruptions and global change, highlighting the need for enhanced recovery methods. This book offers a comprehensive overview of the fascinating field of biocrust research, making it indispensable not only for scientists in this area, but also for land managers, policy makers, and anyone interested in the environment.
The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for assessing the science related to climate change. It provides policymakers with regular assessments of the scientific basis of human-induced climate change, its impacts and future risks, and options for adaptation and mitigation. This IPCC Special Report on Climate Change and Land (SRCCL) is the most comprehensive and up-to-date scientific assessment of the multiple interactions between climate change and land, assessing climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems. It assesses the options for governance and decision-making across multiple scales. It serves policymakers, decision makers, stakeholders, and all interested parties with unbiased, up-to-date, policy-relevant information. This title is also available as Open Access on Cambridge Core.
This volume integrates a conceptual framework with participatory methodologies to understand the complexities of dryland socio-ecological systems, and to address challenges and opportunities for stewardship of future drylands and climate change in the global south. Through several case studies, the book offers a transdisciplinary and participatory approach to understand the complexity of socio-ecological systems, to co-produce accurate resource management plans for sustained stewardship, and to drive social learning and polycentric governance. This systemic framework permits the study of human-nature interrelationships through time and in particular contexts, with a focus on achieving progress in accordance with the 2030 United Nations Agenda for Sustainable Development. The book is divided into four main sections: 1) drylands and socio-ecological systems, 2) transdisciplinarity in drylands, 3) interculturality in drylands, and 4) the governance of drylands. Expert contributors address topics such as pastoralism and the characteristics of successful agricultural lands, the sustainable development goals and drylands, dryland modernization, and arid land governance with a focus on Mexico. The volume will be of interest to dryland researchers, sustainable development practitioners and policymakers.