Landscape modeling using STELLA language

In conclusion, STELLA is user-friendly and accessible to non-experts. However, though the basics are simple, when modelling all elements related to conservation and development outcomes of a landscape some complexity cannot be avoided. Figure 4 shows a part of the TNS landscape model and demonstrates the need for a structural framework for a complex model. Some elements of the model (e.g. “household income” or “elephant population”) can be placed in a frame and considered a sub-model. While it is enclosed in a separate frame, it maintains its relationship with elements outside the frame.

Figure 4. Components of STELLA model

For example, Figure 5 shows a sub model “immigrants” The employment rate influences the immigration into the region, while income loss influences the migration out of the region. The employment rate is calculated in the sub-model “employment” and the loss of income in calculated in the sub-model “household income”. These parameters are than “copied” from one sub-model into the other, or when using STELLA terminology, they are “ghosted” and they appear as dashed circles in the sub-model “immigrants”. The interface of the model when using sub-models now looks like Figure 6. The arrows between the models indicate that a parameter has been “ghosted” from one sub-model into the other, in another way it indicates there is a relationship between the sub-models.

Figure 5. STELLA interface showing sub-model immigrants

Figure 6. STELLA detail showing sub-model immigrants

Some examples are available where the STELLA modelling language was used to build scenarios addressing tradeoffs between conservation and development.

• Exploring the impact of gold mining in SW Ghana

  In South-West Ghana, population pressure is very high and cocoa is the main cash crop. The landscape is a mosaic structure of some natural forest patches (mainly in the productive and non-productive forest reserves) surrounded by cocoa plantations often mixed with secondary forest and some fallow land. The most likely future scenario of change for this landscape would be the opening of a gold mine in the district (as there is in a neighbouring district). A model was build assuming a gold mine boom to occur in 9 years from now and its impact on forest cover and household income was simulated

  Download (PDF size 52 KB).

• Exploring the impact of better governance in SE Cameroon

  South-East Cameroon is a forest rich region with a relatively low population density. Timber extraction is the main economic activity and a 1994 decentralization law decides a share of the forest royalties paid to the government should flow back to the region for development. However, governance issues at the commune level made that the lump sum of this money didn’t reach the poor rural population. A model was built with local NGO’s for the South-East Cameroon landscape showing what could happen if good governance was adapted by the communes.

  English (PDF size 34 KB).

  French (PDF size 37 KB).