Framework for modelling tropical forest dynamics

A framework for modelling the dynamics of tropical forests is described. The framework makes use of simulation models to predict the long term growth and yield of forests under different management regimes. It is designed to have practical application for the sustainable management of forest resources in tropical countries. The framework comprises a suite of simulation models, each of which is appropriate in particular circumstances. Each model uses a disaggregated representation of a forest stand. An individual-based representation is used for trees in the forest stand above a threshold size, while a more aggregate representation (such as a cohort representation) is used for seedlings and saplings. Processes of stand disturbance and recovery from disturbance . are captured. Disturbance results from tree falls and from stand harvesting. Recovery from disturbance may involve seed production, seedling establishment, and competition between trees. Local interactions within the stand are captured, as is species-specific behaviour. The content of each model in the framework is represented in a text-based model design. Details of the content are specified using a formal representation language. The language has semantics and syntax for specifying how a set of generic modelling concepts is employed in an individual model. Details specified in this way include the names and kinds of model variables, and the algorithms used in model calculations. A formal-representation (an 'ontology') of the set of generic modelling concepts developed for use in the framework was created using the Ontolingua server. This provides an unambiguous specification of the modelling concepts used. This assists communication and may also make it easier to design rules and procedures for translating the model content into forms compatible with different modelling systems. The framework has functionality to support the creation, implementation and documentation of new model designs. A standard text editor is used to create and edit new model designs. Designs are processed by tools in the framework to create programs and data sets necessary for use of the model. The Code Generator produces source-code appropriate for implementation of the model. The Source-code Compiler compiles the model source code to create a stand-alone model program. The Parameter Generator creates a parameter file suitable for use with the model and the Description Generator creates a natural language description of the model that is comprehensible, unambiguous and complete. The framework supports the sharing and reuse of model content between models. Model content is packaged into modules that are stored in a special repository. Modules are stored in source-code rather than binary form and are incorporated in model source-code by the Code Generator program. Each module specifies an algorithm used in the model. A common simulation interface is used with all models in the framework. This allows users to conduct simulation runs and vary model parameters. It also provides support for meaningful display of simulation data in graphs, tables and diagrams. Users of the framework can customise the data displays to a high-degree. A case-study showing the application of the framework to an evaluation of alternative silvicultural regimes is reported. The investigation considered the impact of felling cycle length on growth and yield of timber for tropical forest in Kalimantan, Indonesia.