The distribution of logging residues and its impact on seedling establishment and early plant growth in two Norway spruce stands

ABSTRACT

In Fennoscandia, logging residues (LR) are increasingly being harvested to provide fuel for renewable energy. However, the removal of LR is thought to lead to decreased growth in the next generation of trees. The effect on tree growth has generally been obtained by comparing the total removal of residues with retained residues spread evenly on the ground. With current clear-cutting practices, residues can be left with different spatial distributions, confounding the effects of residue removal. Field experiments were, therefore, established at two Norway spruce sites, comprising six treatments with varying distributions and volumes of residues. Before planting seedlings, the sites were disc-trenched. At one of the sites, seedling survival was significantly lower when all residues were removed immediately. At both sites, after 10 years there were statistically significant growth losses after removal of residues. There were no differences in plant growth if the residues were concentrated in small heaps and strings, simulating the normal distribution of LR following stem-only harvesting, compared with residues left evenly spread on the ground. To determine the duration of the observed growth effects, these study sites must be monitored more long term.

KEYWORDS:

• Bio-fuel
• clear-cutting
• final felling
• fuel-adapted felling
• nitrogen
• Picea abies
• whole-tree harvesting

Acknowledgements

We thank the land owners, Bergvik Skog AB and Växjö stifts Egendomsförvaltning, for hosting the field experiments, and all field personnel for collecting samples and performing various tasks over the years. The statistical analysis was performed using SAS software, copyright SAS Institute Inc. SAS and all other SAS Institute Inc. products or service names are registered trademarks or trademarks of SAS Institute Inc., Cary, NC, USA.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funding information: The study was funded by the Swedish Energy Agency [projects 12699-1 and 12699-2] and Skogforsk’s Framework Program.