07-10 June 2010, Potsdam, Germany

Scientific Background and Rationale:
Desertification and land degradation pinpoint a fundamental paradox of dryland ecosystems. On the one hand, dryland plants are, individually, adapted to be resilient. On the other, dryland ecosystems are subject to catastrophic changes. How, therefore, do individually resilient plants succumb to stress in sufficient numbers to cause ecosystem-wide sudden and catastrophic change? If a model of desertification is to have practical application, it must be both quantitative (so that measurable impacts of environmental change can be identified), grounded in knowledge of the propagation and resource requirements of particular species (so that it may be applied at particular localities) and include a quantitative understanding of ecogeomorphological interactions (so that feedbacks can be included within the model). No existing model meets these requirements.

In collaboration with US colleagues, we have been working on processes (Mueller et al., 2007a; 2007b) and have recently developed (Stewart et al, in press) a new approach to understanding the dynamics of dryland vegetation that overcomes both the fundamental weaknesses of scale and the lack of predictive power of the ‘Islands of Fertility’ model and the flaws in existing models for larger scale dryland ecosystems. Our approach is based on the concept of connectivity. We hypothesise that both the form (i.e. patchy) and function (i.e. dynamics) of dryland ecosystems are controlled by the advective flow of resources (e.g. soil, water, nitrogen) and propagules (e.g. seeds) through the landscape, driven by vectors. Advection creates spatial heterogeneities in plant biomass that, in turn, promote the emergence of connected pathways that modify the advective fluxes. Thus, we hypothesize a strongly coupled feedback between advective fluxes and the emergent distribution of vegetation and microtopography in (dis)connected patches. Our approach is an advance on the simplistic approaches based on “toy” models (e.g. Klausmeier, 1999; Reitkerk et al., 2002; Kéfi et al., 2007) because it has been developed in light of decades of field and laboratory research by the investigators into the physical processes that transport resources and propagules in these environments (e.g., Wainwright et al., 2000, 2002; Okin, 2008; Okin and Gillette, 2001; Okin et al., 2006, 2007; Li et al., 2007, 2008; Mueller et al., 2007a, c). Further adaptations of this model will make it applicable to a range of other styles of land degradation, such as the conversion of woodland to matorral or that due to intensive cultivation, which occur more commonly in an EU setting.

Vegetation in dryland environments is patchy. This patchiness is key to the development of connected biophysical processes as discussed above. It is also critical to the productivity of dryland systems. For example, Aguiar and Sala (1999) have demonstrated that patchy vegetation is better able to exploit available water when rainfall is below a specific threshold. However, one critical issue is the scales on which patchiness occurs. In grass-dominated environments, it may be on centimetre-decimetre scale, whereas in shrub-dominated landscapes, characteristic scales are from one to several metres. In areas with low topography and/or savannah-type vegetation, scales of patchiness may be from tens to hundreds of metres. However, because of feedbacks between ecosystem and geomorphic processes, there are commonly multiple scales of patchiness developed within the landscape. Understanding this patchiness therefore affects understanding of the productivity of drylands, but also the ways in which modifications and interventions in environmental management might operate. The use of newly developed ecogeomorphic models to understand these patterns is thus innovative in that it provides novel methods of understanding processes underlying dryland degradation across scales, and therefore providing holistic approaches as per recent scientific and management trends. These methods are based on the most recent complexity science, and uses self-organization as a basis of understanding evolutionary patterns.

To evaluate fully these innovations, a range of data-based and analytical developments are required. As new models are developed, they change the conceptual basis for measurements, and thus evaluations need to be made both of how existing data sets – including those derived from remote sensing – can be implemented for assessing models and what strategies are required for the derivation of new data sets. The production of new data sets and analytical techniques is complicated by the need to bring an interdisciplinary set of expertise together, from geomorphology, hydrology, ecology, computation, remote sensing, spatial statistics and nonlinear dynamics. The aim of the workshop is thus to advance methods for analysis of complex spatio-temporal patterns, both produced by self-organizing models and within environmental data sets.

Impact of Developments on Science:
The multi-scale, patchy and dynamic distribution of vegetation in drylands is an emergent property that arises from complex, poorly understood non-linear relationships between plants, soils and transport processes. The development of better models and evaluation techniques for these patterns will thus provide a significant conceptual and methodological advance. The workshop will allow continuing developments in complex systems from both theoretical and practical perspectives. Inasmuch as ecogeomorphology is interdisciplinary, in enables the distillation of optimal methods from both Newtonian and Darwinian approaches to science.

As well as spatial patterns, connectivity is a linking concept within this work. Connectivity may be seen as both a description of pattern and process, and thus allows more holistic approaches to scientific problems to be developed. In some senses, it may also be considered metaphorically as a linking factor in a disciplinary sense as well as an environmental one.

While the focus in this workshop will be on dryland settings and land degradation within them, there is ultimately the possibility for the transfer of approaches and methods to other environmental settings. For example, work on peat bogs has demonstrated patterns of self-organization (Baird et al., 2008), and similar issues arise in lowland river basins (Rodriguez-Iturbe and Rinaldo, 2001), and in the degradation of heavily used agricultural land (Harris and Heathwaite, 2005).

The Need for European-Scale Collaboration:
Land degradation is a widespread and complex problem, and requires the integration of a range of skills sets to be found across the countries of the EU. Land degradation also occurs in relation to different driving mechanisms, some of which are culturally specific and thus a wide distribution of inputs are required to develop an understanding of how transferable spatially and temporally the approaches are. The number of experts in geoecomorphic systems in the EU is limited, and there is a vital need for bringing together those experts who are working on some aspects of geoecomorphic systems, but have restricted access to emerging new analysis approaches e.g. within data assimilation and modelling tools. While networks addressing land degradation (e.g. DESERT: action) and collaborative projects (e.g. DeSurvey ) exist across Europe, the new methodologies based on complexity theory will potentially add value to these existing services and provide a hub for outside knowledge and expertise to come into the EU. Any form of predictive model or tool requires a wealth of data during its creation and testing. No individual institution or country can achieve an effective model without a combined effort in pulling information together from a variety of dryland ecosystems and eco-niches.

Furthermore, dryland research is not just a priority for those countries in the Mediterranean but also for those individuals based in north and western Europe. Increasingly, rural poverty and ecosystem services are becoming favoured issues for investigation and a workshop on ecogeomorphic systems will help clarify actions needed to meet Europe’s Millennium Assessment goals.

Expected Benefits and Outcomes of the Workshop:
Degradation of drylands is a major issue in the EU. For example, 18 % of land in Spain is designated as having a high or very high threat of desertification, with a further 19 % in the medium-risk category (MMA, 2009). The UNCCD Annex on the Mediterranean suggests there is a threat to all semi-arid zones, making up 63.5% of the land area of Spain, 62% of Greece, 61.5% of Portugal, 40% of Italy and 16% of France. Many of the world’s drylands have undergone land degradation in the recent past, and many areas are projected to be affected by further desertification in the coming decades as a result of climate change. This desertification has caused changes to planetary albedo and promoted expansion of desert areas (Taylor et al., 2002); influenced rates of aeolian erosion and dust emission (Li et al., 2007; Okin, 2008) and affected rates and patterns of water erosion, with consequent socio-economic impacts (Reynolds and Stafford-Smith, 2002). Understanding the dynamics of dryland ecosystems is fundamental to explaining these past changes and to predicting and managing future changes, including their global impacts, both biophysical and socio-economic. The proposers of this workshop have been involved in major developments in understanding land degradation in the US, and the workshop provides an opportunity for the transfer of this technology back to a European setting.

Understanding dryland environments and providing the physical basis for management interventions in them will benefit many of the world’s poorest communities. The results of this project will contribute to the UNCCD 10-year Strategy that includes improved understanding of the biophysical trends relating to land degradation in global drylands and to EU policy needs. In particular, the holistic approaches provided by detailed spatial and temporal modelling techniques with a process basis, provide a means for scientific support of integrated strategies for environmental management, including the EU Water and Soils Framework Directives.

As a key outcome of the workshop, it is planned to initiate the formation of two, inter-connected research networks. The first network will concentrate their efforts of the compilation and cross-analysis of ecogeomorphic data sets from different spatial scales, environments and composition (e.g. plot data or remotely sensed data) thus allowing to assess the types of functional self-organisation that occur within European land degradation studies. The second network will bring together modellers to enable an inter-comparison of spatial modelling tools to reproduce ecogeomorphic systems and to assess degradation and possibly remediation measures for dryland fields across Europe. It is planned that the two newly established groups communicate their advances through an interactive internet platform.

Besides the establishment of continuing networks, we propose to publish a volume which both reflects the state-of-the-art in ecogeomorphic modelling and data, and will act as a manual for the range of innovative techniques evaluated. A major review paper is also projected for a high impact international journal in order to disseminate the results rapidly and broadly. Thus, we aim to disseminate good practice as widely as possible as a result of the workshop. We will also hold discussions about the need for setting up data networks and analytical standards for spatial patterns.

References:

Aguiar, MR and OE Sala 1999 ‘Patch structure, dynamics and implications for the functioning of arid ecosystems’, Trends in Ecosystems and Evolution 14, 273-277.

Baird, A.J., Eades, P.A., and Surridge, B.W.J. 2008. The hydraulic structure of a raised bog and its implications for ecohydrological modelling of bog development. Ecohydrology 1, 289-298, doi: 10.1002/eco.33.

Harris, G, and AL Heathwaite 2005 ‘Inadmissible evidence: knowledge and prediction in land and riverscapes’ Journal of Hydrology 304, 3-19

Kéfi S, Reitkerk M, Alados CL, Pueyo Y, Papanastasis VP, ElAich A, de Ruiter PC 2007 'Spatial desertification patterns and imminent desertification in Mediterranean arid ecosystems', Nature 449, 213-17.

Klausmeier, CA 1999 ‘Regular and irregular patterns in semiarid vegetation’, Science 284, 1826-1828.MMA 2009 ‘Lucha contra la desertificación’,

Li J, Okin GS, Alvarez LJ and Epstein HE 2007 'Quantitative assessment of wind erosion and soil nutrient loss in desert grasslands of the southwestern United States', Biogeochemistry 85 317-332.

Li J, Okin GS, Alvarez LJ and Epstein HE 2008 'Effects of Wind Erosion on the Spatial Heterogeneity of Soil Nutrients in a Desert Grassland of Southern New Mexico', Biogeochemistry, 86, doi: 10.1007/s10533-008-9195-6.

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Mueller, EN, J Wainwright, AJ Parsons 2007b ‘Spatial variability of soil and nutrient characteristics of semi-arid grasslands and shrublands, Jornada Basin, New Mexico’ Ecohydrology DOI: 10.1002/eco.1

Mueller, EN, J Wainwright, AJ Parsons 2007c ‘The impact of connectivity on the modelling of overland flow within semi-arid shrubland environments’ Water Resources Research DOI: 1029/2006WR005006

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Rodriguez-Iturbe, I, and A Rinaldo 2001 Fractal river basins: chance and self-organization Cambr. Univ Press

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Wainwright, J, AJ Parsons and AD Abrahams 2000 ‘Plot-scale studies of vegetation, overland flow and erosion interactions: case studies from Arizona and New Mexico’, Hydrological Processes 14, 2921-2943.

Wainwright, J, AJ Parsons, WH Schlesinger and AD Abrahams 2002 ‘Hydrology-vegetation interactions in areas of discontinuous flow on a semi-arid bajada, southern New Mexico’, Journal of Arid Environments 51, 319-330.