Project information

written by: CASCADE project

introduction   • science and technology objectives   • state of the art   • progress beyond state of the art


Sudden and catastrophic regime shifts in dryland ecosystems

One of the most challenging themes in ecology over the last decades is the quest for the understanding of discontinuous changes in ecosystems. Several terms have been used to indicate such changes, such as ‘sudden regime shifts’, ‘thresholds’, tipping points’, ‘catastrophic shifts’ and ‘critical transitions’. Discontinuous changes have since then been observed and analyzed for a wide variety of ecological systems, including lakes, drylands, peatlands, rangelands, marine systems, and musselbeds.

Some of these discontinuous shifts in ecosystems imply undesired and irreversible changes. For example, shallow lakes can suddenly change into eutrophic systems with a large loss in biological diversity, and drylands can catastrophically lose both biological and economic production.

For this reason, early warning signals can be very helpful to take well-timed adequate and cost-effective measures to prevent undesired sudden shifts. The need of early warning signals has been indicated for e.g. dryland ecosystems and lakes, but it has also been argued that sudden regime shifts will occur without warning. The present proposal will focus on sudden regime shifts in dryland ecosystems. The reasons for this choice are twofold

  • First: Drylands cover about 40% of the terrestrial land surface of the globe, and are home to over two billion people. In Europe, drylands represent over 32% of its land mass and are home to 25% of its population. In both Europe and worldwide, drylands are crucial determinants of the economy, culture and climate.
  • Second: For catastrophic shifts in dryland ecosystems, early warning signals are now being developed, opening perspectives for timely and appropriate measures. Sustainable management of drylands asks for such measures, but should also aim to keep short term costs of measures (e.g. temporary migration of herds) as low as possible without compromising benefits in the long-term. This perhaps more crucial in drylands than in other regions, as livelihoods are often more marginal, and any cost of unnecessary measures is more likely to tip the livelihood balance. 

By focusing on these vulnerable ecosystems, especially by improving our understanding of the drivers, and mechanisms behind shifts and by developing timely signaling tools, we aim to bring the science of sudden shifts in ecosystem a major step forwards and to find ways in which these shifts can be avoided and in which livelihoods can be supported. CASCADE will investigate a range of dryland ecosystems in southern Europe to study a range of physical and socio-economical drivers. This is done by performing research in 6 study sites in the Mediterranean region, ranging from Portugal to Cyprus (Figure 1). More details on these study sites are given in Annex 1.

Figure 1 Study sites of CASCADE

Science and Technology objectives

The aims and objectives of CASCADE are to obtain a better understanding of sudden shifts in drylands that may lead to major losses in biodiversity and concomitant ecosystem services. By focusing on vulnerable drylands as our target ecosystems, we build further on existing knowledge regarding shifts in these ecosystems. CASCADE will improve our understanding of the biogeochemical mechanisms underlying sudden and catastrophic shifts, and of the key biotic and abiotic factors influencing these processes. Based on these analyses, CASCADE will develop ways to predict the proximity of the CASCADE’s dryland ecosystems to thresholds in such a way that these predictions can be used by policymakers and land users for more sustainable management of drylands worldwide.

The specific objectives of CASCADE are

  • To analyse the historical and current state of a series of selected dryland ecosystems in southern Europe in relation to climate and human activities, and the role of thresholds and tipping point in the land degradation processes in these sites (WP2),
  • To experimentally assess on a field microplot scale the interplay between biogeochemical processes, especially the spatial and temporal variation in water and nutrients and how that affects facilitation and competition, underlying tipping points and sudden regime shifts in vegetation structure and composition in the study sites (WP3),
  • To experimentally assess on a field mesocosm scale the interplay between vegetation structures (spatial patterns and composition), hydrology, land use, and sudden regime shifts (WP4),
  • To experimentally assess on a landscape scale the vegetation structure (composition, cover, spatial patterns) and ecosystem services before and after regime shifts, as well as the potential of restoration of degraded systems (WP5),
  • To develop a spatially explicit model that links the empirical observations on the various scales in WP3, WP4 and WP5 to come up with reliable and empirically based indicators of the proximity of the ecosystems to thresholds and sudden shifts (WP6),
  • To design management strategies to deal with tipping points and thresholds in the studied dryland ecosystems and their resilience towards change; these management strategies will be formulated in terms of comprehensive guidelines including principles, best practices, implementation approaches and recommendations (WP7),
  • To integrate socio-economic factors into the ecological model and undertake scenario analyses of land management strategies, including their multi-scale evaluation with policy makers to enable formulation of policy recommendations for preventive and restorative dryland management (WP8),
  • To make the results accessible to the scientific community by means of scientific papers and to local policy makers and land users by means of popular papers and reports; these reports will especially describe the outcome of the integrated modelling, indicators of sudden shifts, and adaptation strategies of local land users in the study sites (WP9),
  • To develop a multi-media communication strategy, including a manual on knowledge transfer and dissemination, a training event for project partners on knowledge transfer and dissemination, a CASCADE website, including an information system to be known as CASCADIS, and a video/film presentations of scientific issues underlying shifts in dryland ecosystems and the management of land degradation (WP9).

State of the art

While interest in and study of ecological thresholds have increased tremendously over the last few decades, the existing understanding of the factors involved and the potential impacts is still largely qualitative, and the science of understanding and predicting them is still in its infancy (CCSP, 2009). At present there are differing points of view regarding definitions for critical thresholds, their existence and the ability to effectively study them. While modelling exercises clearly suggest the existence of thresholds and can generate information regarding impacts, finding supporting evidence in ‘real’ landscapes has met with mixed results. And even where there is considered to be evidence, there is significant discussion and debate about the statistical rigour of current methods and the applicability of results. The complexity of natural systems and processes is recognized as an inherent and confounding factor requiring some different approaches to research in this field, and to the interpretation and utilization of the results in natural resource management as well as socio-economic policy. What has been done and learned to date sheds light on just how immense and complex the field is and how much remains to be learned. There is a great need for advancement on many fronts in order to understand, monitor and manage ecological changes before, during and after thresholds are reached.

CASCADE is addressing this huge challenge in an integrated and holistic way in order to advance the state of knowledge in the research field of ecosystem behaviour, thresholds and tipping-points. While these issues are of importance in many regions of the world, CASCADE will focus explicitly on dryland systems as they are one of the most fragile and threatened ecosystems in Europe. (UNDP, 2010; MEA, 2005).

Progress beyond the state of the art

It is becoming increasingly clear that dryland ecosystems have critical thresholds at which the ecosystem shifts abruptly from one state to another. Such shifts in drylands may imply major losses of biological diversity and ecosystem functioning. It is difficult to predict critical transitions, because of the sudden character of the shifts. Yet, for dryland ecosystems, features of the spatial vegetation patterns may serve as indicators of the proximity of thresholds and shifts.

Key patterns associated with the early stages of degradation in rangelands are the change from grass-dominated to shrub dominated systems with increased bare ground, and shifts to relatively many small vegetation patches, in extreme situation leading to completely unproductive deserts. It is clear that shifts of this character may have important effects on the livelihood of the local populations. In dryland ecosystems, the development of early-warning signals seems possible as there are particular spatial patterns in vegetation structure that can arise before a critical transition. Models of dryland vegetation show that as a critical transition to a threshold is approached, the vegetation takes shapes of regular spatial patterns. These patterns change in a predictable way when nearing the critical point, implying that such patterns may be interpreted as early-warning signals for a sudden shift.

CASCADE will improve the understanding of the biogeochemical mechanisms underlying sudden and catastrophic shifts by carrying out a series of experiments that will provide new knowledge on mechanisms and drivers behind sudden shifts in dryland ecosystems. The experiments will include studies on field microcosm, field mesocosm and landscape scales. Microplot experiments will be conducted to detect the occurrence and establish the strength of facilitation and competition among plants under various environmental conditions. Mesocosm experiments will be carried out in which plant cover and diversity is investigated under various resource availabilities (water and nutrients) and grazing/browsing/wildfire pressures. Field studies will investigate indicators of regime shifts in the CASCADE dryland sites (rangelands, steppes, shrublands, arable land, and woodlands) to assess major changes in vegetation composition and (spatial) structure and related ecosystem services that results in regime shifts. This will lead to the identification of early warning signals for land degradation with a sudden character, of use for natural resource and biodiversity managers, politicians and others.

Furthermore, CASCADE will develop models in which the mechanisms will be based on the abovementioned experimentation. CASCADE will therefore develop new models accounting for multiple pressures on vegetation dynamics and threshold behaviour. Hence, these models are also new in terms that they include different plant species that may differ with respect to their response to a range of abiotic factors. In this way, it becomes possible to express the critical transitions not only in terms of vegetation cover, but also in terms of species composition and biodiversity.

CASCADE’s aim is to come up with effective strategies to predict and prevent critical transition in dryland ecosystems. This asks for ways to make the outcomes of experimentation and models usable for the sustainable management of natural resources, including water, in the drylands under study. The development of strategies that predict and prevent critical transitions in dryland ecosystem, requires early warning signals that are based on a solid understanding of biogeochemical mechanisms and the biotic and abiotic drivers behind the shifts. In the new indicator systems that CASCADE aims to develop, indicators comprise of detectable features of ecosystems that indicate the proximity to thresholds, and that can be adequately used for ecosystem management. These indicators will be linked to associated resources and human activities that can be controlled or at least influenced towards sustainable management. Moreover, when we are able to predict sudden shifts and to come up with measures to prevent shifts, it will be CASCADE’s final challenge to evaluate these in the social and economical context of the particular dryland areas, e.g. in terms of costs and benefits on short and longer time scales. This will be done in close contact with the local land users and policy makers.

The CASCADE approach will develop a common-ground participatory approach that will serve as the basis of the sustainable management of the ecosystems, the biodiversity within these ecosystems, and the services provided by the ecosystems. Such detailed, integrated modeling and participatory evaluation of dryland degradation and its causes and solutions have not been undertaken for European dryland regions yet. Therefore, results of CASCADE will be of direct benefit for natural resource managers in dryland areas, and will provide targeted information, guidance and recommendation for related policy makers as well.

CCSP 2009 - U.S. Climate Change Science Program - Synthesis and Assessment Product 4.2.
UNDP 2010 - The forgotten billion, MDG achievement in the drylands, UNCCD and UNDP, pp. 6.
MEA 2005 - Millenium Ecosystem Assessment. 2005. Ecosystems and Human Well-Being: Biodiversity Synthesis. World Resources Institute, Washington, D.C., pp. 100.