TECHNICAL AND ENVIRONMENTAL ISSUES OF STUMP HARVESTING FOR BIOFUEL PRODUCTION IN LATVIA

This article represents the results of the research project 'Forest energy from small-dimension stands, infra-structure objects and stumps' realized in cooperation between Joint stock company 'Latvijas valsts mezi' (Latvia's state forests), SKOGFORSK (The Forestry Research Institute of Sweden) and Latvian State Forestry Research Institute 'Silava'. The article is covering issues related to the results of stump harvesting field study realized in November, 2008. A scope of the study was to estimate costs of stump harvesting and to evaluate working methods and influencing factors related to extraction of stumps. Better harvesting conditions (flat landscape and lack of stones in soil) led to increased productivity of stump extraction in Latvian trials (5.2 t(dry) (t(dry) - tons of dry mass) of stumps per effective hour (E-0-h)) in comparison to average figures in Scandinavian studies. Load sizes of the forwarder ranged from 5.5 to 9.3 t which is about half of the maximum load of forwarder. Average productivity of forwarding was 6.3 t(dry) E-0-h(-1). Productivity of stump transport (distance - 7 km) was 3.5 t(dry) E-0-h(-1). Productivity of comminution was 10 t(dry) E-0-h(-1). Prime cost of the stump harvesting, including extraction, forwarding, stump transport (7 km one direction), comminution and chip transport (50 km one direction) was 6.3 LVL LVm(-3) (LV - loose volume). 'Environmental footprint' of the stump harvesting in terms of carbon (C) emissions was 2.5 kg C LVm(-3) of wood chips at terminal. Stumps demonstrated considerably higher heat value (5.7 MWh t(dry)(-1) against 4.7 MWh t(dry)(-1) for the hog fuel from a slash).