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Advancing dryland ecohydrology: factors and mechanisms determining catastrophic shifts

Periodic Reporting for period 1 - ECOHYDRY (Advancing dryland ecohydrology: factors and mechanisms determining catastrophic shifts)

Reporting period: 2016-03-01 to 2018-02-28

Dryland ecosystems cover over 45% of the land area on Earth and host more than two billion people. The already fragile delivery of services by these ecosystems is increasingly threatened by global environmental change. Understanding the factors and mechanisms that govern dryland dynamics and their response to changing environmental conditions and antrhropogenic pressures is therefore of utmost importance. The scientific aim of this Action, ECOHYDRY, was to address the ecohydrological processes that determine the stability, resilience and restoration potential of dryland ecosystems. In particular, ECOHYDRY aimed to contribute to the research field of catastrophic ecosystem shifts (i.e. sudden and not easily reversible change in the ecosystem state in response to a gradual increase in pressure) by investigating critical processes and factors such as ecohydrological feedbacks and functional diversity. For achieving its goals, the project used a novel methodological approach coupling mathematical models and field manipulative experiments of dryland ecosystem dynamics. The societal aim of ECOHYDRY was to provide useful and scientifically-sound information to adapt and increase the resilience of dryland ecosystems to global change impacts, including reliable early warning indicators of dryland degradation. In this way, the project directly addressed the two cross-cutting priorities of sustainable development and climate action established by the H2020 Work Programme, reinforcing the already large European competitiveness in dryland research and management.
In the framework of the project, a new conceptual and modelling framework for the study of dryland regime shifts was proposed. This framework integrates two well acknowledged connectivity-mediated ecohydrological feedbacks of opposite sign that operate at different scales: a positive global feedback and a negative local feedback between changes in bare-soil connectivity and vegetation growth at the ecosystem and at the vegetation patch scales, respectively (see diagram below). This framework was used to evaluate the interplay of varying strengths of positive and negative feedbacks on dryland response to environmental pressure, which has been seldom investigated. The methodological approach coupled modelling and manipulative field experiments of dryland dynamics. The modelling outputs showed that increasing strengths of the local negative feedback relative to the global positive feedback decreased the risk of catastrophic shifts. Further, even in case of sudden transitions between healthy and degraded ecosystem states, strong local negative feedbacks seem to largely facilitate the recovery of degraded states with very low vegetation cover. The coupling of modelling and field manipulative experiments offered a unique opportunity to improve the empirical base of the model and to optimise the evaluation of the model predictions. Being aware of the difficulties in translating concepts such as catastrophic shifts to the general public, ECOHYDRY is using a novel participatory approach for dissemination in which the project outcomes are broadly disseminated in the form of “key messages” after being tested for scientific validity and general comprehension by a platform of scientists and stakeholders.
ECOHYDRY has extended the theory of ecosystem structure-function relationships by focusing on the so far less-explored hydrological functions. The project has advanced scientific knowledge on drylands by providing more realistic predictions on dryland dynamics allowing better identification of degradation risk and of attributes increasing resilience of dryland ecosystems to human and climatic pressures. For instance, ECOHYDRY has identified that catastrophic regime shifts to degraded states are less likely to occur in drylands with strong local negative feedbacks linking vegetation cover and runoff-driven redistribution of resources from bare-soil to vegetated patches. Regarding the societal impact, ECOHYDRY results point to new dryland restoration strategies based on the manipulation of ecohydrological feedbacks: strategies that increase the strength of the local feedback by manipulating the biotic structure of the community applied in combination with actions that disrupt the global feedback. Last but not least, an important expected impact of ECOHYDRY is to more effectively communicate scientific knowledge about drylands to society throughout tested key messages, a critical goal for a terrestrial biome of paramount ecological importance whose ecological value is offered overlooked by society.
Dryland ecohydrological feedbacks mediated by runoff resource-redistribution