Silva Fennica vol. 59 no. 3 | 2025

According to the 13th Finnish National Forest Inventory, 0.8 Mha of drained peatland forests require ditch network maintenance (DNM). The annual DNM area has decreased radically during the past ten years, leading to gradual shallowing of ditches and rise of water table (WT) in peatland forests. To study the impacts of ditch shallowing on ecosystem services, we applied Peatland Simulator SUSI for 20 average peatland forests representing four different geographical regions in Finland. The simulation period was 20 years and the initial ditch depths were set to 0.3 m, 0.6 m and 0.9 m. The study included drained peatland forest site types from nutrient rich to nutrient poor, with main species as Scots pine (Pinus sylvestris L.) or Norway spruce (Picea abies (L.) Karst.). We studied how ditch shallowing affected stand volume growth, ecosystem and soil carbon (C) balances, and nitrogen (N) and phosphorus (P) export loads to water courses in different peatland sites. The results showed that due to ditch shallowing, the ecosystem C sinks increased in most sites when the initial ditch depth was 0.6 m or 0.9 m. Ditch shallowing generally increased stand volume growth in Southern Finland when the initial ditch depth was 0.6 m or 0.9 m. Regardless of the location and initial ditch depth, ditch shallowing decreased N and P exports, and soil C emissions. The study calls for new water management guidelines for drained forested peatlands in Finland.

• Saari, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0009-0001-5931-4210 E-mail: annastina.saari@helsinki.fi
• Palviainen, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0000-0001-9963-4748 E-mail: marjo.palviainen@helsinki.fi
• Niemi, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland https://orcid.org/0000-0003-0461-3667 E-mail: mikko.t.niemi@helsinki.fi
• Laurén, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland; Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland https://orcid.org/0000-0002-6835-9568 E-mail: annamari.lauren@helsinki.fi

Energy wood supply has faced significant challenges in Finland in recent years. While forest chip consumption has increased, the cessation of wood imports from Russia has added pressure on the use of domestic forest resources. This study examined the status of energy wood supply to heat-only and combined heat and power (CHP) plants from the perspective of energy wood suppliers. The survey-based study particularly focused on energy wood transport distances, the origin of delivered energy wood, and the proportion of various assortments. The operational environment, including wood fuel storage capacity and policy impacts, was also investigated. The results indicate that most energy wood consumed as forest chips was sourced less than 100 km from the consumer plant. However, these transport distances depended on annual forest chip consumption at the delivery point plant. Notably, energy wood was supplemented by roundwood that otherwise would have been suitable for processing in the forest industry; the proportion of that was 25–33% of all roundwood delivered.  The results of this study also highlighted the visible role of land-use change areas, especially for stump sourcing, while imported wood accounted for only a small fraction of the supply. In conclusion, to reduce the burning of industrial roundwood and to divert energy wood harvesting to young commercial forests, policy should place greater emphasis on the economic viability of harvesting small-diameter trees for energy production. Furthermore, uncertainty in the operational environment, caused by policy changes, should be mitigated.

• Niinistö, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, FI-00790 Helsinki, Finland https://orcid.org/0009-0006-2645-0095 E-mail: tuomas.niinisto@luke.fi
• Anttila, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, FI-00790 Helsinki, Finland https://orcid.org/0000-0002-6131-392X E-mail: perttu.anttila@luke.fi
• Kaseva, Natural Resources Institute Finland (Luke), Tietotie 4, FI-31600 Jokioinen, Finland https://orcid.org/0000-0002-8167-5434 E-mail: janne.kaseva@luke.fi
• Sikanen, Natural Resources Institute Finland (Luke), Yliopistokatu 6b, FI-80100 Joensuu, Finland https://orcid.org/0000-0001-6368-2879 E-mail: lauri.sikanen@luke.fi
• Kärhä, School of Forest Sciences, University of Eastern Finland, Yliopistokatu 7, FI-80101 Joensuu, Finland E-mail: kalle.karha@uef.fi
• Routa, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, FI-00790 Helsinki, Finland https://orcid.org/0000-0001-7225-1798 E-mail: johanna.routa@luke.fi

Managing boreal forests while maintaining biodiversity is challenging due to climate change and increasing resource demands. Retention forestry, in which some trees are deliberately left during harvesting, mitigates the negative impacts of clearcutting, but it remains unclear whether regeneration can be ensured as tree retention levels increase. This study assessed Scots pine (Pinus sylvestris L.) regeneration over 4.5 years in the southern boreal zone of Sweden (Effaråsen) under five treatments: four tree retention levels (3%, 10%, 30%, 50%) and a 50% retention treatment with prescribed burning. Mechanical site preparation (MSP) and regeneration methods were key drivers of success in Scots pine forest regeneration. MSP consistently and positively influenced all regeneration variables (height, growth, survival, germination, and recruitment) across planting, seeding, and natural regeneration. Direct seeding produced the highest number of seedlings per hectare, while planting yielded the tallest seedlings with high survival. Natural regeneration produced fewer and smaller seedlings and was insufficient to ensure stand establishment. Stand-scale retention levels generally did not affect regeneration, but retained trees within 20 meters negatively affected the height, growth, and survival of planted and seed-germinated seedlings, likely due to competition, indicating a proximity effect. Burned areas showed greater height and survival, suggesting that prescribed burning enhances regeneration by reducing competition while potentially creating habitat relevant for conservation and specialized species. Overall, the results highlight that retention trees intended for biodiversity have a limited role as seed trees for regeneration, and careful planning is needed to use them for biodiversity purposes without negatively impacting regeneration.

• Lariviere, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden; Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden https://orcid.org/0000-0002-1415-3476 E-mail: delphine.lariviere@slu.se
• Djupström, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden; Swedish University of Agricultural Sciences (SLU), Department of Wildlife, Fish and Environmental Studies, Umeå SE-901 83, Sweden https://orcid.org/0000-0003-4536-7765 E-mail: line.djupstrom@skogforsk.se
• Nilsson, The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-268 90 Svalöv, Sweden https://orcid.org/0000-0002-5632-6523 E-mail: oscar.nilsson@skogforsk.se

Reliable forest inventory methods are important for informed management. The current study compared the quality of forest attribute models based on metrics from image matching point clouds, generated using various software packages, with those based on metrics from airborne laser scanning. The field- and remotely sensed data used in the analyses were collected as part of an operational forest management inventory in Norway. Results indicate that models based on point cloud data from airborne laser scanning (ALS) consistently produced smaller root mean square error values, demonstrating superior accuracy in capturing complex forest structures compared to models using image matching point clouds. While image matching offers advantages such as lower costs and broader area coverage, this data source primarily represents canopy surfaces, which complicate its use in inventories requiring detailed canopy information. Statistical analyses revealed no significant differences in model performance among various image matching software, but all being inferior to ALS. The study emphasizes the importance of selecting the appropriate source of remotely sensed data based on specific inventory needs.

• Bollandsås, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, Norway https://orcid.org/0000-0002-1231-7692 E-mail: ole.martin.bollandsas@nmbu.no
• Gobakken, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, Norway https://orcid.org/0000-0001-5534-049X E-mail: terje.gobakken@nmbu.no
• Næsset, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, Norway E-mail: erik.naesset@nmbu.no
• Roald, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, Norway E-mail: bjorn-eirik.roald@nmbu.no
• Ørka, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, 1430 Ås, Norway https://orcid.org/0000-0002-7492-8608 E-mail: hans-ole.orka@nmbu.no

The aim of this study was to experimentally test the most favourable seeding times for Scots pine (Pinus sylvestris L.), and to compare Scots pine and lodgepole pine (Pinus contorta Douglas ex Loudon) in respect to suitable seeding times and site factors. The experimental area was located in Sodankylä, Central Finnish Lapland. Generalized linear mixed effects models with binomial distribution assumption were applied to model the presence or absence of a seedling at a seeding point. The study shows that in addition to spring and early summer, direct seeding of Scots pine can also be carried out during late autumn or even early winter (October and November) in northern Fennoscandia. On the contrary, seeding in late summer and early autumn (August and September) is much less successful and cannot be recommended as such, but can be used if the amount of seeding material is increased to compensate the loss. There is more flexibility for lodgepole pine for which the proper seeding period seems to be from spring through to late autumn. Whether lodgepole pine seeds were stratified or not had no statistically significant effect on regeneration success. Our results clearly indicate that lodgepole pine is less susceptible to unfavourable site and soil factors than Scots pine. Our results give support to extend the period of direct seeding from the present early summer to another period in late autumn and even early winter.

• Hyppönen, Natural Resources Institute Finland (Luke), Ounasjoentie 6, FI-96200 Rovaniemi, Finland E-mail: mikkokthypponen@gmail.com
• Hallikainen, Natural Resources Institute Finland (Luke), Ounasjoentie 6, FI-96200 Rovaniemi, Finland https://orcid.org/0000-0001-5384-8265 E-mail: ext.ville.hallikainen@luke.fi
• Bergsten, Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences (SLU), Skogsmarksgränd, SE-901 83 Umeå, Sweden E-mail: burskog@gmail.com
• Winsa, Natural Resources Institute Finland (Luke), Ounasjoentie 6, FI-96200 Rovaniemi, Finland E-mail: hans.winsa@gmail.com
• Miina, Natural Resources Institute Finland (Luke), Yliopistokatu 6 B, FI-80100 Joensuu, Finland https://orcid.org/0000-0002-8639-4383 E-mail: jari.miina@luke.fi
• Valkonen, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, FI-00790, Helsinki, Finland https://orcid.org/0000-0002-2879-4821 E-mail: sauli.valkonen@luke.fi
• Helenius,  Natural Resources Institute Finland (Luke), Tietotie 4, FI-31600 Jokioinen, Finland E-mail: psjhelenius@elisanet.fi
• Jaskari, Natural Resources Institute Finland (Luke), Ounasjoentie 6, FI-96200 Rovaniemi, Finland E-mail: ejaskari@gmail.com
• Rautio, Natural Resources Institute Finland (Luke), Ounasjoentie 6, FI-96200 Rovaniemi, Finland https://orcid.org/0000-0003-0559-7531 E-mail: pasi.rautio@luke.fi

Low tract size (ha) and harvested volume per hectare (m³ ha^–1) decrease the cost-efficiency of today’s conventional Nordic harvesting systems, which generally consists of a harvester and a forwarder. Low cost-efficiency is a problem because it reduces forest owners’ incentive to harvest wood and manage their forests. Today’s conventional harvesting system (two-machine system; TMS) was developed based on rotation forest management. As continuous cover forestry (CCF) grows in the Nordics, it is necessary to develop harvesting solutions that can operate cost-efficiently even when total removal (m³ per tract) is low. Single-machine systems (SMS) require only one machine to do all the harvesting activities; thus, SMS have only one machine-relocation cost per tract, instead of two per tract for TMS. SMS are generally categorized as either harwarders or dual machines, the difference being if the machine processes the logs directly onto the load space or not. In relation to TMS, the relative competitiveness of SMS increases with decreasing tract size, harvested volume per hectare, and/or average extraction distance. Because of site adaptation, CCF, and ever-expanding forest road networks, the trend in Nordic forestry over the last few decades has been that these three factors have been decreasing. CCF mainly entails thinning from above, which generally means the harvesting of large trees. SMS exist today, but almost exclusively as small-sized dual machines that cannot cut large trees. Thus, there is a pronounced need for commercially available SMS that can fell and process large trees.

• Ersson, SLU, School of Forest Management, SE-739 21 Skinnskatteberg, Sweden https://orcid.org/0000-0003-2442-7482 E-mail: back.tomas.ersson@slu.se
• Manner, Skogforsk, Uppsala Science Park, SE-751 83 Uppsala Sweden https://orcid.org/0000-0002-4982-3855 E-mail: jussi.manner@skogforsk.se
• Kärhä, School of Forest Sciences, University of Eastern Finland (UEF), P.O. Box 111, FI-80101 Joensuu, Finland E-mail: kalle.karha@uef.fi