An evaluation of wood fuel production parameters from Irish Sitka spruce first thinnings

A comprehensive study of a number of in-forest wood energy supply chains was undertaken to collect empirical data on many aspects of both the stand and operational parameters therein. The data was then used to develop statistical models, so that a number of harvesting systems could be compared in a simulated environment. The simulated environment had two factors: the mean diameter at breast height (dbh) of the stand (cm), and the mean extraction distance (m). The harvesting systems compared were: cut to length (CTL) harvesting, CTL harvesting with chipping of the pulp assortment, and whole tree harvesting with terrain chipping of the whole trees. Not only were models developed on the productivity of the machines, but a taper equation, dbh to total height model, and a set of dbh distribution models were developed to predict the volumes of the assortments attributable to each harvesting system down to the tree level. The productivity models then used this data to estimate a cost of production per hectare for the harvesting systems. A value per unit volume of the assortments was taken from literature, and a profit analysis performed for each harvesting system. The simulation results show that whole tree harvesting and terrain chipping returns the highest positive profit for all levels of mean dbh at short extraction distances, but suffered from the machine interaction in the terrain chipping system at long extraction distances. The machine interaction between the terrain chipper and the chips forwarder was analysed using discrete event simulations. CTL harvesting and chipping of the pulp assortment returned the highest positive profit at longer extraction distances.