Modeling stand, harvest, and machine interactions caused by harvesting prescriptions.

摘要

Partial cutting is being increasingly used as a harvesting method to address public concerns about timber harvesting. Such operations, however, can increase the difficulty of felling and harvesting trees since less volume is removed and the residual stand must be protected. An interactive computer simulation program was developed to model stand, harvest, and machine factors and evaluate their interactions while performing felling, skidding, or forwarding activities. The approach used in this system relied on interactive graphical simulation techniques written with Visual Basic Version 4.0, an event-driven programming language that runs under Microsoft Windows 95 environment. The program was written based on the principles of software engineering. An object-oriented structure model was employed with a three-level hierarchy (project, modules, and procedures) with built-in methods and custom controls. The hierarchy of this interactive simulation program (project) consisted of 28 form modules and a standard module. Each form module contained one or more procedures. Each procedure included one or more methods and custom controls. About 80 event and general procedures with 1800 methods and controls were included in the program, some of which were represented as objects in the process of object-oriented programming.; A stand generator was built to allow the user to generate either natural or planted stands and perform the harvesting simulation conveniently and economically. Five machines (chainsaw, move-to-tree feller-buncher, swing-to-tree harvester, grapple skidder, and forwarder) were modeled in the system for performing felling and extraction operations. Simulations were performed by moving machine images within stand maps or an extraction plot on the computer screen. The residual stand, machine running paths, and extraction machine travel intensity were simultaneously recorded and saved in the data files for later analysis.; The interactions of stand types, harvesting methods, and different equipment were evaluated in an experiment using this interactive simulation program. Three harvesting systems (chainsaw/grapple skidder, feller-buncher/grapple skidder, and harvester/forwarder) were examined performing clearcuts, shelterwood cuts, and single-tree selection cuts in a natural stand and a planted stand. Elemental time, distance traveled, travel intensity, productivity, and cost estimates were obtained for each combination of stand, harvest, and equipment. Results indicated the relative efficiency and feasibility of using partial cutting instead of clearcutting.