Long-term scheduling of harvesting with adjacency and trigger constraints
The forest harvesting problem, FHP, is described. A review of the existing literature is presented along with an analysis of the strengths and limitations of various attempted solutions. The diversity of model evident in recent papers is noted. The difference is explained between a strategic model that sets long-term harvesting goals in terms of total area to be cut each year, and a tactical model that produces a short-term schedule of actual blocks. Special attention is devoted to the development of FRI’s Forestry-Oriented Linear Programming Interpreter, FOLPI, which is currently used to formulate an LP model of the strategic planning problem. Reasons are presented for the desirability of an integrated model, embracing both strategic and tactical decisions, which is capable of optimisation. Accordingly the project then proceeds to a thoughtful and detailed construction of such a model. Particular care is taken to examine the status and function of FOLPI within this model.
A column generation algorithm is then developed to solve the relaxed linear program formulation. Finally powerful constraint branching techniques are utilised to obtain the desired optimal solution to the integrated model. Throughout the development of the project the Whangapoua forest in Coromandel, New Zealand has been used as a case study. A concluding section presents numerical output from some of the exhaustive computational analysis associated with this application.