Current issue: 53(2)
Under compilation: 53(3)
Operating conditions affecting the quality of spot mounding by Bracke continuously advancing mounders were investigated on 66 regeneration areas (124 ha) in eastern Finland. The quality of mounds was classified as suitable (good or acceptable after additional compression) or unsuitable for planting. Models were constructed for the number of suitable planting spots obtained per hectare (good and acceptable mounds), the probability of successful mounding (≥1600 planting spots ha–1) and the probability of creating a suitable mound as a function of terrain, site and soil characteristics, as well as slash conditions (removed, fresh or dry logging residues). The average number of mounds created was 1892 ± 290 mounds ha–1, of which 1398 ± 325 mounds ha–1 (74%) were classified as suitable for planting. The quality of spot mounding was reduced by steep terrain, a thick humus layer and fresh logging residues. Stoniness and soil texture also affected the number of planting spots created. Mounding after logging residues had dried increased the number of planting spots by 191 spots ha–1 compared with mounding in the presence of fresh residues. Removing residues did not significantly increase the number of planting spots compared with mounding amongst dry residues. A thick humus layer, very stony soil, steep slopes and valley terrain decreased the number of planting spots by 150–450 spots ha–1. The number and quality of mounds varied considerably according to the operating conditions, but with careful selection of timing and sites the quality obtained by a continuously advancing mounder can be improved.
Harvesting residues collected from the final cuttings of boreal forests are an important source of solid biofuel for energy production in Finland and Sweden. In the Finnish supply chain, the measurement of residues is performed by scales integrated in forwarders. The mass of residues is converted to volume by conversion factors. In this study, weather based models for defining the moisture content of residues were developed and validated. Models were also compared with the currently used fixed tables of conversion factors. The change of the moisture content of residues is complex, and an exact estimation was challenging. However, the model predicting moisture change for three hour periods was found to be the most accurate. The main improvement compared to fixed tables was the lack of a systematic error. It can be assumed that weather based models will give more reliable estimates for the moisture in varying climate conditions and the further development of models should be focused on obtaining more appropriate data from varying drying conditions in different geographical and microclimatological locations.
In Finland the increasing use of biofuel in transport presupposes a search for new raw material sources for biorefining. The aim of this study was, at the regional level, to compare the procurement costs of logging residues, stumps, delimbed stems and cereal straw for biorefining. The accumulation and procurement costs of forest chips and cereal straw were estimated within a 100-kilometre transporting distance via existing road network from an end-use-facility located in Kouvola in South-East Finland. The analyses were performed as simulated treatments in thinnings of young stands, cereal fields and regeneration fellings using existing productivity and cost functions and yield calculations based on crop statistics, the forest industry stand data and the sample plots data of the National Forest Inventory of Finland. Accumulation of raw material assortments and costs of production stages were defined per dry tonnes. Subsidies and raw material prices were excluded from consideration in the study. The results indicate that recovering logging residues requires lower costs than utilization of stumps, delimbed stems or cereal straw. Cereal straw represents an important source of biomass in Kouvola but the cost competiveness is poor compared the procurement costs of forest chips. When the annual procurement volume of biomass was 50 000 dry tonnes the cost at the plant was 49 € dry tonne –1 and biomass was comprised totally of logging residues. Procurement cost grew to 59 € dry tonne –1 when the annual procurement volume of biomass was doubled to 100 000 dry tonnes. Of that amount, the proportion of logging residues was 58.4%, stumps 24.3% and delimbed stems 17.3%. First cereal straw dry tonnes were delivered to end-use-facility, when procurement cost grew to 60 € dry tonne –1 and annual procurement volume of biomass was 110 000 dry tonnes.