Harvesting system simulation using a systems dynamic model

To compete in the current work environment in the southeastern United States, forestry companies and logging contractors must manage their harvest systems to ensure efficient production. Efficiency in this case can be defined in terms of tons of wood produced per unit of system cost. Site and system factors affect the output from a stand and affect the efficiency of different harvesting systems. A model was developed that can simulate harvesting system production efficiency with changing stand and terrain parameters. Four common southeastern US harvesting systems were included in the model. The model includes functions, adjustable by the user, that quantify the efficiency of each harvest system is measured with respect to terrain parameters (slope and average extraction distance), as well as stand parameters (average tree diameter, stocking intensity, and harvest intensity). By adjusting any of these parameters, it is possible to compare the four harvest systems and to perform various sensitivity analyses. Result examples presented in the article include change in productivity with increasing tree size, productivity changes of a cut-to-length system in varied silvicultural conditions, as well as the associated evaluation of the cost of inefficiency of each system.