The effect of timber harvesting guidelines on felling and skidding productivity in Northern Minnesota

Substantial investment has been made in the development and application of scientifically based best management practices (i.e., guidelines) intended to protect and enhance the ecological, environmental, and aesthetic attributes of forest resources. When correctly applied, guidelines can increase environmental benefits on site and to adjacent resources, as well as improve forest health and productivity. We empirically evaluated how varying degrees of application of Minnesota's Timber Harvesting and Forest Management guidelines, along with operator and tract-specific variables, affect felling and skidding productivity of mixed aspen/hardwood/ conifer stands in northern Minnesota. To do so, felling and skidding productivity data from five mechanized logging businesses were collected on 52 clearcut harvest blocks in northern Minnesota from August 2006 to May 2007 using time-motion and geospatial sensors. Additional postharvest data were collected for each block using high-resolution aerial photography and detailed on-site inventories. With use of these data, separate regression models were developed to estimate the impact that timber harvesting guidelines and tract and operator variables have on felling and skidding productivity. Results of regression analyses and diagnostic tests showed that felling productivity is influenced not only by guideline variables but also by tract and operator variables. Skidding productivity is influenced by both guideline and tract variables. The error terms of the separate felling and skidding models are statistically correlated, calling for their simultaneous estimation using a method known as seemingly unrelated regression. Specific explanatory variables that are statistically significant in explaining felling productivity include the logger's use of a preharvest site map and/or preharvest meeting with the forester, harvesting in winter, merchantable timber volume per unit area, and the operator. Variables that are statistically significant in explaining skidding productivity are the area of landings and skid trails as a percentage of the harvest area, ratio of the harvest block perimeter to the block area, slope, and merchantable timber volume per unit area. The findings suggest that implementing the guidelines we studied has minimal effect on felling productivity, although several adversely affect skidding productivity. By considering how to lay out the harvest block to facilitate skidding efficiency, a feller operator may be able to reduce the impact of some guidelines on skidding productivity.