Damage to saplings in mechanized selection cutting in uneven-aged Norway spruce stands

Abstract

Damage to 0.5–2.5 m saplings in selection cuttings in uneven-aged Norway spruce stands was studied in three stands in Finland. Harvest removals were 96–122 m³ha⁻¹ or 32–41% of initial basal area. Harvesting was carried out with one-grip harvester and forwarder in March–April 2007. The strip road network had been established in previous cuttings. Before harvesting, trees higher than 2.5 m were measured and mapped with coordinates. Saplings 0.5–2.5 m were measured on circular sample plots of 10 m² on a square grid, where line and plot intervals were 7.07 m. Trees to remove were selected with a computerized tree selection procedure and marked before cutting. Factors affecting the probability and severity of injury to an individual sapling were studied with logistic regression models. Percentage of injured saplings was 17.6, 29.8, and 61.0%, depending on study stand. Stem breakage was the most common type of injury. Distance of the sapling from the nearest strip road, sapling height, harvested basal area within 25 m of the sapling, and the distance to the nearest remaining tree were statistically significant factors in the model of the probability of injury. In the model for the severity of injury, only the distance from the nearest strip road and the sapling height were significant. Saplings near strip roads were vulnerable during both cutting and forwarding, and they often ended up under slash or logs. Development in working methods and machinery are potentially effective in reducing sapling damage in selection cuttings.

Keywords:

• Mechanized harvesting
• sapling damage
• selection cutting
• spatial analysis

Acknowledgements

The research was funded by the Finnish Cultural Foundation. Harvesting operations were carried out by Piiroset Ky. We thank all the persons involved in the field measurements: Mr. Kalle Karosto, Mr. Kari Kautto, Mr. Antti Miettinen, Ms. Kaisa Pienihäkkinen, Mr. Erkki Salo, and Mr. Veijo Salo. We are also thankful for Mr. Leo Tervo for harvesting arrangements; Dr. Risto Ojansuu for providing support for modeling; Ms. Virpi Alenius for comments on statistical analysis; Ms. Hannele Saloseutu for typing the data; and Ms. Essi Puranen for layout work.