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Articles by Pekka Niemelä

Category : Article

article id 5584, category Article

Tarmo Virtanen, Seppo Neuvonen, Pekka Niemelä, Ari Nikula, Martti Varama. (1996). Climate change and the risks of Neodiprion sertifer outbreaks on Scots pine. Silva Fennica vol. 30 no. 2–3 article id 5584. https://doi.org/10.14214/sf.a9229

Keywords: Pinus sylvestris; climate change; GIS; Neodiprion sertifer; cold tolerance; winter temperatures; insect outbreaks

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The European Pine Sawfly (Neodiprion sertifer Geoffroy) is one of the most serious defoliators of Scots pine (Pinus sylvestris L.) in northern Europe. We studied the pattern in the regional occurrence of the outbreaks of N. sertifer in Finland in years 1961-90, and made predictions about the outbreak pattern to the year 2050 after predicted winter warming. We tested whether minimum winter temperatures and forest type and soil properties could explain the observed outbreak pattern. We analysed outbreak patterns at two different spatial levels: forest board- and municipal-level.

The proportion of coniferous forests on damage-susceptible soils (dry and infertile sites) explained a significant part of the variation in outbreak frequency at small spatial scale (municipalities) but not at large spatial scale (forest boards). At the forest board level, the incidence of minimum temperatures below -36 °C (= the critical value for egg mortality) explains 33% of the variation in the outbreak pattern, and at the municipal level the incidence of cold winters was also the most significant explaining variable in northern Finland. Egg mortality due to cold winters seems to be the most parsimonious factor explaining why there have been so few N. sertifer outbreaks in northern and north-eastern Finland. We predict that climate change (increased winter temperatures) may increase the frequency of outbreaks in eastern and northern Finland in the future.

Virtanen, E-mail: tv@mm.unknown
Neuvonen, E-mail: sn@mm.unknown
Niemelä, E-mail: pn@mm.unknown
Nikula, E-mail: an@mm.unknown
Varama, E-mail: mv@mm.unknown

Category : Research article

article id 964, category Research article

Liisa Huttunen, Matthew P. Ayres, Pekka Niemelä, Susanne Heiska, Riitta Tegelberg, Matti Rousi, Seppo Kellomäki. (2013). Interactive effects of defoliation and climate change on compensatory growth of silver birch seedlings. Silva Fennica vol. 47 no. 3 article id 964. https://doi.org/10.14214/sf.964

Keywords: root; shoot ratio; biomass; Betula pendula; elevated CO2; elevated temperature; folivory

Highlights: The main components affecting growth compensation in silver birch seedlings are the timing and severity of foliage damage; The ability to compensate growth is also dependent upon the limits of temperature and nutrient availability; The responses of birches imply that folivory does not necessarily lead to reduced net productivity under changing climate

Abstract | Full text in HTML | Full text in PDF | Author Info

Atmospheric warming increases the abundance of insect herbivores and intensifies the risk of defoliation, especially in high latitude forests. At the same time, the effects of increasing temperature and CO₂ on plant responses to foliage damage are poorly understood. We examined if previous-year defoliation, varying between 0 and 75% of total leaf area, and different combinations of elevated temperature, CO₂ and nutrient availability alter the growth of two-year old silver birch (Betula pendula Roth) seedlings. We measured the greatest height growth in seedlings that were fertilized and defoliated twice at the level of 50% of total leaf area, and subjected to elevated temperature with ambient CO₂. The lowest growth was recorded in unfertilized seedlings that were defoliated twice at the level of 25% of total leaf area, and grew under ambient temperature with ambient CO₂. The total biomass increased in all seedlings that were fertilized or grew under elevated temperature. The root: shoot ratios were low in defoliated seedlings, or seedlings subjected to fertilization or temperature elevation. Our conclusion is that ability of birches to compensate height growth is highly dependent upon the magnitude and frequency of defoliation on the limits of temperature and nutrient availability. These responses imply that folivory does not necessarily lead to reduced net productivity of trees under changing climate.

Huttunen, Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku, Finland E-mail: liisa.huttunen@utu.fi
Ayres, Biological Sciences, Dartmouth College, Hanover, NH 03755, USA E-mail: matt.ayres@dartmouth.edu
Niemelä, Section of Biodiversity and Environmental Science, Department of Biology, University of Turku, FI-20014 Turku, Finland E-mail: pekka.niemela@utu.fi
Heiska, The Finnish Forest Research Institute, Punkaharju Unit, Finlandiantie 18, FI-58450 Punkaharju, Finland E-mail: susanne.heiska@metla.fi
Tegelberg, Digitarium - Digitization Centre of the Finnish Museum of Natural History and the University of Eastern Finland, Joensuu Science Park, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: riitta.tegelberg@helsinki.fi
Rousi, The Finnish Forest Research Institute, Vantaa Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: matti.rousi@metla.fi
Kellomäki, Faculty of Science and Forestry, School of Forest Sciences, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: seppo.kellomaki@uef.fi

article id 151, category Research article

Janne Miettinen, Pekka Helle, Ari Nikula, Pekka Niemelä. (2010). Capercaillie (Tetrao urogallus) habitat characteristics in north-boreal Finland. Silva Fennica vol. 44 no. 2 article id 151. https://doi.org/10.14214/sf.151

Keywords: forest management; forestry; grouse; thinnings; landscape composition

Abstract | View details | Full text in PDF | Author Info

This study aimed to identify tools for taking capercaillie habitats into consideration in forest management. This would provide new alternatives for ecologically more sustainable forest management. Capercaillie summer and winter locations, from wildlife monitoring counts (1998–2004) in northern Finland, and reference, non-capercaillie locations were combined with forest planning data, and the area proportions of different landscape classes in an 800-m radius circle surrounding capercaillie and reference locations were compared. Thinning stands (in summer and winter) and spruce mires (in summer) were more abundant in capercaillie habitats than in reference landscapes, whereas e.g. seedling stands, mature stands and waste land areas were less abundant. The relative habitat use was highest in mean tree diameter (DBH) classes from 10.5 to 14.5 cm in summer habitats of adult capercaillie in heath forests, whereas in peatland forests, in brood habitats and in winter habitats it peaked in diameter classes 14.5 to 18.5 cm. The tree layer density was positively associated with the relative habitat use. A trend of lower habitat use was detected in the largest diameters (17–40 cm) in comparison to middle-sized diameters (10–16 cm) in heath forests, but not in peatland forests. Relatively young managed forests (age 30–40 years or more) can form suitable capercaillie habitats in north-boreal forests. However, this suitability is not necessarily permanent. Understorey management, longer rotations and multicohort forest management are suitable tools for capercaillie habitat management, because they can increase the available cover close to the ground, canopy cover, overall forest cover at the landscape scale and bilberry cover.

Miettinen, Finnish Game and Fisheries Research Institute, Finland E-mail: janne.miettinen@rktl.fi
Helle, Finnish Game and Fisheries Research Institute, Finland E-mail: ph@nn.fi
Nikula, Finnish Forest Research Institute, Finland E-mail: an@nn.fi
Niemelä, University of Turku, Dept of Biology E-mail: pn@nn.fi

article id 182, category Research article

Janne Miettinen, Pekka Helle, Ari Nikula, Pekka Niemelä. (2009). Changes in landscape-scale habitat selection of capercaillie (Tetrao urogallus) in managed north-boreal forest. Silva Fennica vol. 43 no. 4 article id 182. https://doi.org/10.14214/sf.182

Keywords: forestry; landscape composition; capercaillie; wildlife triangle

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We studied changes in habitat selection of capercaillie in northern Finnish boreal forests at two spatial scales during two time periods, 1989–1992 and 2000–2003. We studied capercaillie densities and their changes between the study periods in relation to the landscape class proportions within 3-km buffer zones around the wildlife triangle center points. Furthermore, we compared the landscape class proportions in 800-meter buffer zones around capercaillie wildlife triangle count observations and around the counted wildlife triangle transects using t-tests and compositional analysis. At the local population scale (3 km) the change in adult density between the study periods was associated positively with the proportion of young thinning stands in 2003 and reversely with the mature stand (1992 and 2003) and clear-cut (1992) proportions. Capercaillie juvenile and pooled densities during 2000–2003 were positively associated with the advanced thinning stand proportion in 2003. At the capercaillie home range scale (800 m) habitats were rich in mature stands during 1989–1992 in relation to available habitats, but not during 2000–2003 when young thinning stands were more abundant in relation to available habitats. Relatively young managed forests can be suitable for capercaillie, but mature managed forests as capercaillie habitats may have deteriorated between the study periods. Spatial planning may help to form suitable areas that are large enough for the species, but the highest potential may lay in the forest stand scale, where increased cover on the ground could promote the habitat quality.

Miettinen, Kankurinhaka 14, FI-90450 Kempele, Finland E-mail: janne.miettinen@rktl.fi
Helle, Finnish Game and Fisheries Research Institute, Tutkijantie 2 E, FI-90570 Oulu, Finland E-mail: ph@nn.fi
Nikula, Finnish Forest Research Institute, Rovaniemi Research Unit, Eteläranta 55, FI-99600 Rovaniemi, Finland E-mail: an@nn.fi
Niemelä, University of Turku, Department of Biology, FI-20014 University of Turku, Finland E-mail: pn@nn.fi

article id 469, category Research article

Henri Vanhanen, Timo O. Veteli, Sonja Päivinen, Seppo Kellomäki, Pekka Niemelä. (2007). Climate change and range shifts in two insect defoliators: gypsy moth and nun moth – a model study. Silva Fennica vol. 41 no. 4 article id 469. https://doi.org/10.14214/sf.469

Keywords: insects; forest pests; CLIMEX; Lymantria monacha; Lymantria dispar; poleward shift; geographical range

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Environmental factors influenced by global climate change determine the distribution ranges of organisms. Especially ectothermic animals are expected to shift their distribution ranges northwards in the next hundred years or so. In this study simulations made with CLIMEX-modelling software were used to predict the future distribution ranges of two Central European serious forest pest species: the nun moth (Lymantria monacha L. (Lepidoptera: Lymantriidae)) and the gypsy moth (L. dispar L). The software calculates an ecoclimatic index based on the life cycle requirements of a species and thus represents the probability of a viable population to exist at a certain location. Three different climate warming scenarios were considered: temperature increase of 1.4, 3.6 and 5.8°C. Simulations generated with the current climate conditions corresponded well to the current distributions of the species. The climate warming scenarios shifted the northern boundary of the distribution for both of these species north by c. a. 500–700 km. Also the southern edge of the ranges retracted northwards by 100–900 km. The results of this study are in agreement with the results of empirical studies on other species. Being serious pest species, these species pose a potential threat to silviculture and therefore, have to be considered in the planning of forest management practices.

Vanhanen, Faculty of Forestry, University of Joensuu, P.O.B. 111, FI-80101 Joensuu, Finland E-mail: hv@nn.fi
Veteli, Faculty of Biosciences, University of Joensuu, P.O.B. 111, FI-80101, Joensuu, Finland E-mail: timo.veteli@joensuu.fi
Päivinen, Faculty of Forestry, University of Joensuu, P.O.B. 111, FI-80101 Joensuu, Finland E-mail: sp@nn.fi
Kellomäki, Faculty of Forestry, University of Joensuu, P.O.B. 111, FI-80101 Joensuu, Finland E-mail: sk@nn.fi
Niemelä, Faculty of Forestry, University of Joensuu, P.O.B. 111, FI-80101 Joensuu, Finland E-mail: pn@nn.fi

article id 499, category Research article

Mikhail V. Kozlov, Pekka Niemelä. (2003). Drought is more stressful for northern populations of Scots pine than low summer temperatures. Silva Fennica vol. 37 no. 2 article id 499. https://doi.org/10.14214/sf.499

Keywords: Pinus sylvestris; climate change; precipitation; stress; temperature; fluctuating asymmetry; Kola peninsula

Abstract | View details | Full text in PDF | Author Info

Needle fluctuating asymmetry, which is a non-specific stress indicator, was used to evaluate responses of Scots pine (Pinus sylvestris L.) to annual climatic variation in the Kola Peninsula, NW Russia, during 1992–1999. Although the 30 trees surveyed for this study demonstrated individualistic responses to the temperature and precipitation of the growth seasons, at the population level we found no effect of temperature and a significant increase in fluctuating asymmetry with a decline in precipitation during the previous August. This finding suggests that the vitality of Scots pine populations at the northern tree limit is controlled by late summer precipitation rather than by temperatures of the growth season.

Kozlov, Section of Ecology, University of Turku, 20014 Turku, Finland E-mail: mikoz@utu.fi
Niemelä, Forestry Faculty, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland E-mail: pn@nn.fi

article id 660, category Research article

Erkki Annila, Bo Långström, Martti Varama, Risto Hiukka, Pekka Niemelä. (1999). Susceptibility of defoliated Scots pine to spontaneous and induced attack by Tomicus piniperda and Tomicus minor. Silva Fennica vol. 33 no. 2 article id 660. https://doi.org/10.14214/sf.660

Keywords: Scots pine; defoliation; Scolytidae; Diprionidae; induced attack; Tomicus piniperda; Tomicus minor; Diprion pini

Abstract | View details | Full text in PDF | Author Info

In 1990–1991, Diprion pini extensively defoliated Scots pine (Pinus sylvestris L.) trees in Lauhanvuori National Park in southwestern Finland. Many trees lost all their foliage, while others had ca. 10% foliage left after the second year of defoliation. Outside the national park, many nearby stands were also heavily defoliated in 1990, but were sprayed with diflubenzuron (Dimilin®) in 1991. This protected the current year needles, corresponding to ca 30% of full foliage. In spring 1992, pine trees with 0, 10, 30 and 100% foliage remaining (10 small and 10 large trees in each category) were baited with pine bolts to induce stem attacks by pine shoot beetles. All baited trees were attacked by Tomicus piniperda and some by T. minor. The attacks failed in all these trees except those that were totally defoliated and some of the small trees with 10% foliage left. Many unbaited trees escaped attack entirely, but only totally defoliated trees were successfully colonized (i.e. produced brood). Attack densities and brood production figures peaked in baited, large and totally defoliated trees. None of the measures (cambial electrical resistance, resin flow, induced lesion length by fungal inoculation, amount of hydrocarbons or phenolic compounds) used to describe tree vigour at the time of attack gave better information than the estimated remaining foliage. We conclude that the risk for beetle-induced mortality following defoliation is a function of remaining needle biomass and beetle pressure. Even at high beetle densities (as was simulated by baiting of trees), trees with 10% of the foliage remaining were able to defend themselves against attacking pine shoot beetles.

Annila, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: erkki.annila@metla.fi
Långström, Swedish University of Agricultural Sciences, Dept of Entomology, P. O. Box 7044, S-750 07 Uppsala, Sweden E-mail: bl@nn.fi
Varama, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: mv@nn.fi
Hiukka, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: rh@nn.fi
Niemelä, University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland E-mail: pn@nn.fi

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