Recovery rates of logging residue harvesting in Norway spruce (Picea abies (L.) Karsten) dominated stands

A significant amount of logging residues is available for recovery in clear-cut areas. The forest residues’ potential has usually been estimated using biomass models. In Norway spruce (Picea abies) dominated stands, a large share of material is left on site especially due to dropping of needles as residues are left on site to dry in small heaps. In this study, we compared the measured dry weight of logging residues at a power plant with the potential biomass estimations made at a stand level. The study was performed in eight Norway spruce dominated stands, three of which were located in eastern Finland (North Karelia region) with the remainder being in Central Finland. The dry weights of branches, needles and stem tops were estimated using biomass models developed for individual trees by Repola et al. [1]. These dry weights were also compared with Swedish biomass models produced by Marklund [2]. The diameter and tree height information of each harvested tree served as input data in these model-based computations. Tree diameter information was obtained straight from the harvester’s stem value files, while the height information was obtained from models using the data from the stem value files as input. Inventory data before logging was used as a control material for harvester based estimates to spot possible measurement errors on the harvester measurement data. In addition, inventory data were used to get the crown height information, which was not available in the harvester measurement data. It was found that the average recovery rate was approximately 62% when applying Repola’s et al. [1] models and 61% when applying Marklund’s [2] models. However, variation between the logging sites was high. According this study, at least a third of the residues remains on the logging site if they are seasoned during the spring and summertime in small heaps.     

Impacts of changing the minimum diameter of roundwood on the accumulation of logging residue in first thinnings of Scots pine and Norway spruce

The aim of this study was to examine the impacts of different minimum top diameters of roundwood on the accumulation of logging residue in first thinnings of Scots pine and Norway spruce. The aim was also to compare estimates of residue accumulation calculated by tree-specific models with field measurements from thinnings. Felling experiments were performed in young pine and spruce stands to evaluate the model calculations. The felling was performed by a harvester with a single-grip harvester head. Sample trees were felled and processed to a minimum diameter of 12, 10, 8 and 6 cm and the delimbed branches and stem wood between these cutting points were weighed. The mean relative masses of the tree tops of spruce were nearly doubled with each increment of 2 cm in the top diameter. Respectively in pine, the mean relative tree top mass was increased by 50-60% when the top diameter was increased by 2 cm. The mass of total residue (tree top and all delimbed branches) was similarly increased, but the differences were not as large. Compared to pine, smaller variation in the crown mass of the spruce sample resulted in a more accurate model prediction of the mass of tree tops and total residue. The results of this study suggest that the biomass quantity and distribution of a small amount of trees cannot be predicted very reliably, but when these results are generalized to stand-level, the model predictions can be improved to a practicable level.