Evaluating ecosystem models as tools for policy development on biodiversity (Defra project IF0103)
Aim of the project:
The aim of this project was to evaluate whether ecosystem scale modelling approaches could be used as tools to develop policy to meet biodiversity targets. The project focussed on producing a framework for the selection and development of models that can be used to predict how plausible changes in land-use might impact on biodiversity.ilability of appropriate data will be a particular problem that Defra may have to address when considering future projects to model how changes in land-use impact on biodiversity.
Approaches and summary of conclusions
We initially categorised and reviewed existing models and modelling approaches according to trophic level, separately considering models for vegetation, invertebrates and farmland birds. From these reviews we identified that most existing models considered only single species, often at inappropriate spatial scales for the wide-scale modelling of changes in land-use, and that existing models rarely included interactions between trophic levels. Thus there is a need to develop models that include multiple species and trophic levels and the interactions between them, based on quantitative data.
To allow the incorporation of multiple species and trophic levels, there is a need to be able to integrate data and models across spatial, temporal and ecological scales. A wide diversity of mathematical and statistical modelling approaches exist to tackle the integration of data in this way, with the specific approach required being dependent on the focus of the modelling exercise and the available data. Modelling approaches used in existing studies of the impact of land-use changes on biodiversity were reviewed, most being based on expert opinion rather than quantitative data, and rarely incorporating data across several spatial scales
We therefore needed to ensure that our proposed modelling framework assisted both in the selection of appropriate techniques and the identification of available and necessary data sources, according to the outcome information required to address any particular policy question.
Proposed Modelling Framework
1) What is the current spatial distribution of the species of interest?
2) What is the potential spatial distribution of the species of interest given the changes in land-use?
Our proposed modelling framework, to develop models to determine how plausible changes in land-use might impact on biodiversity, is defined by a set of five key questions:
3) How much of the potential spatial distribution can the species of interest achieve (within a defined time scale), taking account of habitat and landscape permeability?
4) Are there sufficient resources to allow the species of interest to establish in the new locations (within a defined time period)?
5) Will the species of interest establish, and if so how will it affect the current community? (ecological interactions)
The modelling approaches required to answer these questions will need to be selected according to the policy question being asked, the level of spatial detail required, and the level of detail of the available data.
The progression through the questions requires increasing detail to be included within the model. Questions 1 and 2 can be answered using quite broad scale data, and for a relatively large geographical region, though models at this scale will only be able to assess potential changes in biodiversity on this large spatial scale. Question 3 requires more localised spatial data, as it requires knowledge of the potential movement of species and will therefore be subject to variation caused by habitat composition (although it should be possible to aggregate the information to provide summaries over wider spatial scales). Questions 4 and 5 certainly require information at a smaller spatial scale, since they involve questions about species interactions with the local environment.
Answers to all 5 questions will enable the development of models to provide the most useful and detailed information on how changes in land-use will impact on biodiversity. Predictions from these models of the outcomes associated with ranges of plausible future scenarios can then be used to inform or develop policy on particular issues of interest.
Having defined the framework within which ecosystem modelling approaches could be applied to address policy questions, there was a further need to define a clear process within which to apply the modelling framework. This includes the definition of clear, unambiguous targets or hypotheses (under specified land-use scenarios and timescales) to be evaluated using modelling.
The key stages in the process are:
a. What is the precise question to be answered, specified both at an overall policy level and at a practical implementation level?
1. Define and clarify the policy problem or question to be addressed:
b. What definition(s) of biodiversity (species richness, community composition, density of key indicator species) will be used, and how should multiple measures be combined?
c. What spatial scale is of interest, over what geographical region?
d. Over what time scale should land-use changes and biodiversity impacts be considered?
e. How are changes in biodiversity to be measured and presented?
2. Develop plausible future land-use scenarios:
b. What are the likely spatial distributions of these changes?
3. Select modelling approaches (based on data availability) to answer the framework questions, allowing for any required species interactions:
b. What is the potential spatial distribution of the species of interest after land-use changes?
c. How much of the potential spatial distribution can the species achieve (within a defined time period)?
d. Are there sufficient resources to allow the species to establish in the new distribution (within a given time period)?
e. Will the species establish, and if so how will it affect the current community?
4. Simulate the plausible future scenarios and analyse model outputs.
a. Provide list of model assumptions.
5. Make recommendations based on analysis of model output.
b. Provide measures of uncertainty on outputs.
c. Rank scenarios in terms of being most beneficial (or least harmful) to biodiversity.
Together the modelling framework and the above process provide a pragmatic structured approach to producing models to inform and assist in the development of policy on land-use changes, with regards to their impacts on biodiversity. This approach fits well with the ALMaSS modelling approach developed in Denmark, which consists of a landscape and weather simulator, combined with farm management information. Models of individual species are then linked to the landscape simulator, providing a modular approach to developing models of the impacts of landscape change on species abundance, movement and distribution.
Consultation with Defra provided a number of example policy questions. These questions focussed on specific Public Service Agreement and England Biodiversity Strategy targets. It is possible to use the approach described above to provide potential distributions for individual UK priority species under a range of land-use change scenarios, using existing data (where it is available). It will not be possible to determine achievable distributions unless more data on species dispersal and habitat permeability are collected.
For biodiversity conservation, there would almost certainly be a need to consider multiple species, rather than individual species. Although the modelling techniques and tools exist to incorporate species interactions into models, there is a lack of data on interactions between different species.
The availability of appropriate data will be a particular problem that Defra may have to address when considering future projects to model how changes in land-use impact on biodiversity. Where appropriate data are not available, either data will have to be collected as part of the project, or the project will have to develop the model in the absence of data, possibly based on expert opinion. Such projects should, however, also provide clear recommendations on the data that need to be collected to fully parameterise the developed model, and the data collection and subsequent use of the model for decision making should incorporate the concepts of adaptive resource management, allowing iterative improvements in models and decisions as greater information and data become available.
This work was funded by Defra and the final report is available from the Defra website (project IF0103) Download report
For further information please contact Andrew dot Mead at warwick dot ac dot uk