Additional research products (ARP1): GRAZER digital simulation model (prototype)

Authors:

Prof. John Thornes, KCL (UK), Prof. Vasilios Papanastasis, AUTH (Greece), Dr. Inés Fonseca, KCL (UK), Dr. A. Younas, KCL (UK)

The GRAZER model is the prototype for an innovative simulation of grazing behaviour for rangeland, forest and marginal lands in Mediterranean and other semi-arid environments.

It has been developed within the DeSurvey project as a contribution to understanding the vulnerability of marginal lands with respect to desertification, and provides one important conceptual underpinning to the development of the vulnerability model in DeSurvey (MP3). These land use types are thought to be among the least resilient, lacking buffering capacity against land degradation due to centuries of misuse and abuse, through neglect and/or over-exploitation.

Efforts to minimise land degradation in the Mediterranean have been undermined by a multitude of issues, namely the diversity of pastoral systems, the complexity of the ecosystem, paradoxical EU policies, and the interaction of all of the above in a historical context. Thus, it is not surprising that modelling becomes the obvious choice to tackle the complexity of erosion and land degradation phenomena. GRAZER has been developed to provide estimates of levels of erosion and biomass uptake by grazing animals, using an innovative approach, and this first prototype is a conceptual exploration of the fundamental relationships that still has considerable potential for further development.

Grazing in the Mediterranean, and other parts of the world, has often been seen as responsible for degradation of land resources mainly through biomass uptake, which leaves soil exposed to the elements and consequently, more prone to erosive phenomena. However, it has been demonstrated elsewhere that livestock husbandry cannot be responsible for the ills of the Mediterranean and that whilst excessive grazing can have negative impacts on the ecosystem; its restriction can also have adverse impacts and increase the vulnerability of rangelands to more and more intense fires. Moreover, excessive grazing is sometimes the result of agricultural encroachment onto grazing lands, and other deleterious national and EU policies.

Additionally, ontological and theoretical discussions of the concept of carrying capacity, as well as paradigm shifts in rangeland ecosystem equilibrium theories and vegetation succession have also contributed to compound the issue of grazing management. In any case, it is becoming ever more urgent to provide sustainable solutions which optimise livestock production whilst conserving the ecosystem resources. Given the complexity of the grazing problem, modelling with a sound biophysical basis is perhaps the best method to assess the costs and benefits of different grazing management solutions, and show the impact of different management scenarios and/or future changes in climate.

There is a wealth of models for intensive livestock production and some for extensive rangeland, but none for the semi -extensive livestock production, that is ubiquitous in Mediterranean rangeland systems. GRAZER therefore fills the need for a fresh and relevant approach. It contains four main components:

Soil Hydrology (rainfall-runoff model)
Plant-growth
Grazing (includes all animal related processes, including feeding and landscape distribution)
Management (includes pastoral systems and all the infra-structure required to support grazing, i.e. sheds, water points, etc.)

The figure below shows the four main components of Grazer and how these are connected. Thus, changes in management options, such as herd size are used as inputs in the grazing component, which, in turn, affects both plant growth and soil hydrology, which provide feedback directly to the grazing component and indirectly to the management component.

For further information contact: Mike Kirkby