Articles by Annamari Laurén

The effects of nitrogen (N) fertilization on tree growth have been studied widely in boreal forests in Finland, but a quantitative synthesis is still lacking. We performed a quantitative synthesis on volume growth responses to N fertilization in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands in experiments established on mineral soils across Finland. Our study employed findings of 9 published studies including 108 Scots pine and 57 Norway spruce observations covering a wide range of N fertilization treatments, as well as forest stand- and climatic conditions. Based on these observations, we built linear mixed models to describe the N fertilization-induced annual volume growth response of Scots pine and Norway spruce stands. Our models showed that the N dose was the best predictor for volume growth response, and the growth response increased linearly with increasing N dose for both tree species. The volume growth responses also increased along with an increase in mean annual precipitation. The annual volume growth response decreased with the time since fertilization. For Scots pine, the best model also contained site fertility; increase in site fertility increased the volume growth response. These findings emphasize the need for site-specific precision fertilization schemes to sustainably improve growth and carbon sequestration of boreal forests.

• Jetsonen, Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland https://orcid.org/0009-0006-4878-8951 E-mail: johanna.jetsonen@helsinki.fi
• Laurén, Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland; Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0002-6835-9568 E-mail: annamari.lauren@helsinki.fi
• Peltola, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0003-1384-9153 E-mail: heli.peltola@uef.fi
• Laurén, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland; University of Helsinki, Faculty of Medicine, Haartmaninkatu 8, 00290 Helsinki, Finland https://orcid.org/0009-0009-4677-9826 E-mail: katariina.lauren@helsinki.fi
• Launiainen, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, 00790 Helsinki, Finland https://orcid.org/0000-0001-6611-6573 E-mail: samuli.launiainen@luke.fi
• Palviainen, Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland https://orcid.org/0000-0001-9963-4748 E-mail: marjo.palviainen@helsinki.fi

We studied the spatial evenness of nitrogen (N) fertilizer and the effects of fertilization intensity on the short-term volume growth responses in two ground-fertilized Scots pine and two airborne-fertilized Norway spruce study sites on mesic (Myrtillus-type) upland forests in Eastern Finland. We also studied the relationships between measured fertilizer dose, N concentrations in the needles and soil organic (humus) layer, and volume growth of the trees. In each study site, we established three replicate 1 ha blocks for each fertilization treatment (0, 150 and 200 kg N ha^–1). Each block contained three 200 m² circular plots. The spatial evenness of the fertilizer was measured using textile funnels. The height, breast height diameter and vitality of the trees were measured annually. The nutrient concentrations in the needles and humus layer were measured once. Differences between the target and measured fertilizer doses were 3–10% for Scots pine and 11–22% for Norway spruce. At the Scots pine and Norway spruce sites, the volume growth was 0.4–2.1 and 1.8–2.6 m³ ha^–1 a^–1 higher with fertilization, respectively. The fertilizer dose correlated with the N concentrations in the needles and humus layer, and volume growth. Significant volume growth responses to the fertilization (p < 0.05) were found only in the Scots pine at Ilomantsi, possibly due to variations in the initial volume and the fertilizer dose realized between and within treatments. We expect that the differences in volume growth responses between fertilization treatments will increase over time.

• Muhonen, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland https://orcid.org/0009-0007-4051-8567 E-mail: ollmu@uef.fi
• Peltola, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland https://orcid.org/0000-0003-1384-9153 E-mail: heli.peltola@uef.fi
• Laurén, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland; University of Helsinki, Department of Forest Sciences, Latokartanonkaari 7, FI-00014 Helsinki, Finland https://orcid.org/0000-0002-6835-9568 E-mail: annamari.lauren@helsinki.fi
• Ikonen, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland https://orcid.org/0000-0003-1732-2922 E-mail: veli-pekka.ikonen@uef.fi
• Nevalainen, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland https://orcid.org/0009-0000-2972-4385 E-mail: juha.hs.nevalainen@gmail.com
• Pikkarainen, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland https://orcid.org/0000-0001-5301-3639 E-mail: laura.pikkarainen@uef.fi
• Kilpeläinen, University of Eastern Finland, School of Forest Sciences, Yliopistokatu 7, FI-80101 Joensuu, Finland https://orcid.org/0000-0003-4299-0578 E-mail: antti.kilpelainen@uef.fi
• Launiainen, Natural Resources Institute Finland, Bioeconomy and Environment, Latokartanonkaari 9, FI-00790 Helsinki, Finland https://orcid.org/0000-0001-6611-6573 E-mail: samuli.launiainen@luke.fi
• Palviainen, University of Helsinki, Department of Forest Sciences, Latokartanonkaari 7, FI-00014 Helsinki, Finland https://orcid.org/0000-0001-9963-4748 E-mail: marjo.palviainen@helsinki.fi

The aim of this study was to investigate the short-term effects of nitrogen (N) fertilization intensity on the ground vegetation cover and soil chemical properties  in two Scots pine (Pinus sylvestris L.)  and two Norway spruce (Picea abies (L.) Karst.) dominated stands on upland forest sites in Eastern Finland. The fertilizer was applied using a helicopter in the spruce stands and a forwarder in the pine stands. The distribution and the amount of fertilizer was measured with funnel traps. Cover of each species of ground vegetation was estimated  before fertilization and 3–4 years after it in pine and 2–3 years after it in spruce stands. Further, the cover observations were aggregated by plant types. Based on measurements, we analyzed the effects of the funnel-trap-observed amount of N fertilizer on the cover and plant type composition of ground vegetation and soil N and C concentration. In addition, we analyzed  the impacts of competition caused by trees on the ground vegetation cover based on competition indices. N fertilization increased the cover of herbaceous plants and decreased the cover of mosses and dwarf shrubs, and the total cover of ground vegetation. Further, it increased the N concentration of the mor humus layer. The magnitude of the changes increased with the intensity of the N fertilization. The competition caused by trees did not affect the cover of ground vegetation.

• Jetsonen, Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland E-mail: johanna.jetsonen@helsinki.fi
• Laurén, Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland; Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0002-6835-9568 E-mail: annamari.lauren@helsinki.fi
• Peltola, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland E-mail: heli.peltola@uef.fi
• Muhonen, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0009-0007-4051-8567 E-mail: olli.muhonen@forestvital.com
• Nevalainen, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0009-0000-2972-4385 E-mail: juha.hs.nevalainen@gmail.com
• Ikonen, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0003-1732-2922 E-mail: veli-pekka.ikonen@uef.fi
• Kilpeläinen, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0003-4299-0578 E-mail: antti.kilpelainen@uef.fi
• Tuittila, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland E-mail: eeva-stiina.tuittila@uef.fi
• Männistö, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0003-3869-6739 E-mail: elisa.mannisto@uef.fi
• Kokkonen, Faculty of Science and Forestry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland https://orcid.org/0000-0003-0197-2672 E-mail: nicola.kokkonen@uef.fi
• Palviainen, Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 University of Helsinki, Finland E-mail: marjo.palviainen@helsinki.fi