Reusing legacy FORTRAN in the MOTTI growth and yield simulator

MOTTI is a stand-level decision support tool for assessing the effects of alternative forest management practices on growth and yield and on forest management profitability. It is capable of predicting growth responses to silvicultural practices. The MOTTI simulator produces growth and yield information covering the development and structure of growing stock and deadwood by tree species, the amount and structure of cutting removals and natural mortality, and predictions of the biomass dynamics of different tree compartments. The profitability of alternative management schedules can be analysed on the basis of information about cutting removals, user-defined timber prices and management costs at alternative discount rates. This paper describes the structure and components of MOTTI and the development strategy and implementation of the application. Based on practical experience in reusing old applications as subcomponents of MOTTI and expanding the current development project from a simple growth simulator to a multiple-use application, it was concluded that even old pieces of program code are useful if they are of high quality and properly documented.