SCOPE Project on Tree-Grass Dynamics

Project Summary Report, March 1999

Documents Available:

1. Introduction and Summary (below)

2. Workshop 2 Summary Report: Models, data and experiments, Santa Barbara, May 1998

3. Workshop 2 Detailed Report = Working paper 1: Issues in savanna theory and modelling

4. Modelling Workshop 1 Summary Report: Modelling the Mulga Data, South Africa, November 1998

5. Modelling Workshop 1 Detailed Report = Working Paper 2: Modelling tree-grass ecosystems, testing and comparing the approach of four savanna models.

 

Introduction and Summary

Terrestrial ecosystems co-dominated by trees and grass occupy at least 20% of the global land surface, of which the majority are in the form of tropical savannas (Scholes & Hall, 1996). These systems support about one-fourth of the world’s population and are under great land-use pressure, yet the balance of species is highly sensitive to change, thus the knowledge and understanding of the present and future biological state of these areas is of major significance. There is already a body of theory and issues related to the functioning of these systems (Scholes & Archer, 1997), but there has never been a large-scale synthesis of a wide variety of data to test them conclusively. Existing partial syntheses tend to stress the differences between study sites rather than highlighting the common and unifying underlying forces. The time is therefore ripe for a data and theory-driven synthesis exercise. Furthermore, due to the complexity of these systems and their dynamic nature, many of the theories and questions can only be tested or answered using computer modelling techniques.

In 1994 a SCOPE project was launched to assess our understanding of these systems - their dynamic equilibrium and the complex interactions between the tree and grass components, their environment and disturbance. This is to be achieved through data synthesis, statistical analyses and modelling. The SCOPE group was formed to bring together data holders from a wide variety of tree-grass systems, and ecosystem models capable of handling both tree and grass components and the interactions between them and their environment. This SCOPE group is uniquely positioned to address questions of tree-grass dynamics due to the combined experience in the field and with modelling activities. This will be the first large-scale savanna data synthesis, and also the first savanna model synthesis.

The first SCOPE tree-grass workshop was held in Paris in 1996. Initially 37 potential savanna data sets were identified, and four models. The owners of the models and data sets agreed to commit to an inter-comparison exercise. The second workshop in May 1998 was the first of two funded by NCEAS (National Centre for Ecological Analysis and Synthesis, Santa Barbara, USA). It identified in more detail availability of data sets and the format for data synthesis, the nature of the data analysis and modelling experiments, how these would be carried out, and what kind of product(s) would result. A scientific paper is in preparation based on the outcome of this meeting (Working paper 1: Issues in savanna theory and modelling). The first modelling workshop was held in September 1998, hosted and funded by CSIRO, South Africa, and this was followed up by a mini meeting at King’s College in London. All four models were run using one of the identified data sets with different tree density treatments to ensure all models were running well, to improve understanding of the different models and their approaches, to test them against real data and to begin to examine savanna theory issues. This has led to the preparation of a second scientific paper (Working Paper 2: Modelling tree-grass ecosystems, testing and comparing the approach of four savanna models). The third workshop will be funded and hosted by NCEAS around October 1999 to report on progress, review the data analyses and plan further syntheses. This would lead to furhter scientific papers. Ideally the group would like to produce a SCOPE synthesis book.

The Aims

Timetable

Scientific Advisory Committee

Steve Archer, Texas A & M University, USA

Mike Cougenhour, NREL, Colorado State University, USA

David Hall, King’s College London, UK

Jean-Claude Menaut, ORSTOM, France

William Parton, NREL, Colorado State University, USA

Robert Scholes, Forestek, CSIR, South Africa

References:

Scholes R.J. and Hall D.O. (1996) The carbon budget of tropical savannas, woodlands and grasslands. In: Breymeyer A.I., Hall D.O., Melillo J.M. and Agren G.I. (Eds.) Global Change: Effects on Coniferous Forests and Grasslands, SCOPE Volume 56. Wiley, Chichester. pp. 69-100.

Scholes R.J. and Archer S.R. (1997) Tree-grass interactions in savannas. Annu. Rev. Ecol. Syst. 28, 517-544.