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Articles by Tapani Repo

Category : Article

article id 5590, category Article
Heikki Hänninen, Seppo Kellomäki, Ilkka Leinonen, Tapani Repo. (1996). Overwintering and productivity of Scots pine in a changing climate. Silva Fennica vol. 30 no. 2–3 article id 5590. https://doi.org/10.14214/sf.a9235
Keywords: Pinus sylvestris; climate change; ecosystems; frost damage; phenology; forest ecology; gap-type model; model accuracy; model realism; overvintering
Abstract | View details | Full text in PDF | Author Info

The productivity of Scots pine (Pinus sylvestris L.) under changing climatic conditions in the southern part of Finland was studied by scenario analysis with a gap-type forest ecosystem model. Standard simulations with the model predicted an increased rate of growth and hence increased productivity as a result of climatic warming. The gap-type model was refined by introducing an overwintering sub-model describing the annual growth cycle, frost hardiness, and frost damage of the trees. Simulations with the refined gap-type model produced results conflicting with those of the standard simulation, i.e., drastically decreased productivity caused by mortality and growth-reducing damage due to premature dehardening in the changing climate. The overwintering sub-model was tested with frost hardiness data from Scots pine saplings growing at their natural site 1) under natural conditions and 2) under elevated temperature condition, both in open-top chambers. The model predicted the frost hardiness dynamics quite accurately for the natural conditions while underestimating the frost hardiness of the saplings for the elevated temperature conditions. These findings show that 1) the overwintering sub-model requires further development, and 2) the possible reduction of productivity caused by frost damage in a changing climate is less drastic than predicted in the scenario analysis. The results as a whole demonstrated the need to consider the overwintering of trees in scenario analysis carried out with ecosystem model for boreal conditions. More generally, the results revealed a problem that exists in scenario analysis with ecological models: the accuracy of a model in predicting the ecosystem functioning under present climatic condition does not guarantee the realism of the model, nor for this reason the accuracy for predicting the ecosystem functioning under changing climatic conditions. This finding calls for the continuous rigorous experimental testing of ecological models used for assessing the ecological implications of climatic change.

  • Hänninen, E-mail: hh@mm.unknown (email)
  • Kellomäki, E-mail: sk@mm.unknown
  • Leinonen, E-mail: il@mm.unknown
  • Repo, E-mail: tr@mm.unknown
article id 5583, category Article
Ilkka Leinonen, Heikki Hänninen, Tapani Repo. (1996). Testing of frost hardiness models for Pinus sylvestris in natural conditions and in elevated temperature. Silva Fennica vol. 30 no. 2–3 article id 5583. https://doi.org/10.14214/sf.a9228
Keywords: Pinus sylvestris; climate change; frost hardiness; Scots pine; temperature; dynamic models; photoperiod; climatic warming
Abstract | View details | Full text in PDF | Author Info

Two dynamic models predicting the development of frost hardiness of Finnish Scots pine (Pinus sylvestris L.) were tested with frost hardiness data obtained from trees growing in the natural conditions of Finland and from an experiment simulating the predicted climatic warming. The input variables were temperature in the first model, and temperature and night length in the second. The model parameters were fixed on the basis of previous independent studies. The results suggested that the model which included temperature and photoperiod as input variables was more accurate than the model using temperature as the only input variable to predict the development of frost hardiness in different environmental conditions. Further requirements for developing the frost hardiness models are discussed.

  • Leinonen, E-mail: il@mm.unknown (email)
  • Hänninen, E-mail: hh@mm.unknown
  • Repo, E-mail: tr@mm.unknown
article id 5518, category Article
Heikki Hänninen, Seppo Kellomäki, Kaisa Laitinen, Brita Pajari, Tapani Repo. (1993). Effect of increased winter temperature on the onset of height growth of Scots pine: a field test of a phenological model. Silva Fennica vol. 27 no. 4 article id 5518. https://doi.org/10.14214/sf.a15679
Keywords: Pinus sylvestris; height growth; frost damage; bud burst; climatic change
Abstract | View details | Full text in PDF | Author Info

According to a recently presented hypothesis, the predicted climatic warming will cause height growth onset of trees during mild spells in winter and heavy frost damage during subsequent periods of frost in northern conditions. The hypothesis was based on computer simulations involving a model employing air temperature as the only environmental factor influencing height growth onset. In the present study, the model was tested in the case of eastern Finnish Scots pine (Pinus sylvestris L.) saplings. Four experimental saplings growing on their natural site were surrounded by transparent chambers in autumn 1990. The air temperature in the chambers was raised during the winter to present an extremely warm winter under the predicted conditions of a double level of atmospheric carbon dioxide. The temperature treatment hastened height growth onset by two months as compared to the control saplings, but not as much as expected on the basis of the previous simulation study. This finding suggests that 1) the model used in the simulation study needs to be developed further, either by modifying the modelled effect of air temperature or by introducing other environmental factors, and 2) the predicted climatic warming will not increase the risk of frost damage in trees as much as suggested by the previous simulation study.

The PDF includes an abstract in Finnish.

  • Hänninen, E-mail: hh@mm.unknown (email)
  • Kellomäki, E-mail: sk@mm.unknown
  • Laitinen, E-mail: kl@mm.unknown
  • Pajari, E-mail: bp@mm.unknown
  • Repo, E-mail: tr@mm.unknown
article id 5437, category Article
Tapani Repo. (1991). Rehardening potential of Scots pine seedlings during dehardening. Silva Fennica vol. 25 no. 1 article id 5437. https://doi.org/10.14214/sf.a15591
Keywords: Pinus sylvestris; frost resistance; acclimatization; quiescence; impedance
Abstract | View details | Full text in PDF | Author Info

The ability of one-year old Scots pine (Pinus sylvestris L.) seedlings to reharden during the dehardening period was studied. Naturally hardened quiescent seedlings were preconditioned at 0°C for ten days and then placed in chambers at different forcing temperatures with different light regimes. The forcing periods were followed by cool periods. Changes in frost hardiness were monitored at intervals using freeze tests of whole plants. Frost hardiness was assessed by three methods: impedance, survival and growth retardation. Dehardening seemed to be a partially reversible process, i.e. in some growing conditions slight rehardening was found.

The PDF includes an abstract in Finnish.

  • Repo, E-mail: tr@mm.unknown (email)
article id 5433, category Article
Marja-Leena Valkonen, Heikki Hänninen, Paavo Pelkonen, Tapani Repo. (1990). Frost hardiness of Scots pine seedlings during dormancy. Silva Fennica vol. 24 no. 4 article id 5433. https://doi.org/10.14214/sf.a15587
Keywords: Pinus sylvestris; frost hardiness; cold hardiness; annual cycle; chilling requirements; bud dormancy; rest
Abstract | View details | Full text in PDF | Author Info

The relationships between bud dormancy and frost hardiness were examined using two-year-old Pinus sylvestris L. seedlings. The chilling temperatures used were +4 and -2°C. To examine the dormancy release of the seedlings, a forcing technique was used. Frost hardiness was determined by artificial freezing treatments and measurements of electrical impedance. At the start of the experiment, the frost hardiness of the seedlings was about -25°C. After the rest break, the seedlings kept at +4°C dehardened until after eight weeks their frost hardiness reached -5°C. At the lower chilling temperature (-2°C) the frost hardiness remained at the original level. When moved from +4 to -2°C, seedlings were able to reharden only after the time required for bud burst in the forcing conditions had reached the minimum.

The PDF includes an abstract in Finnish

  • Valkonen, E-mail: mv@mm.unknown (email)
  • Hänninen, E-mail: hh@mm.unknown
  • Pelkonen, E-mail: pp@mm.unknown
  • Repo, E-mail: tr@mm.unknown
article id 5351, category Article
Tapani Repo. (1988). Physical and physiological aspects of impedance measurements in plants. Silva Fennica vol. 22 no. 3 article id 5351. https://doi.org/10.14214/sf.a15508
Keywords: developmental stage; electrical impedance; cross-sectional area; frost resistance; temperature acclimation; physiology
Abstract | View details | Full text in PDF | Author Info

Electrical impedance characteristics of plant cells are dependent on such physiological factors as physiological condition, developmental stage, cell structure, nutrient status, water balance and temperature acclimation. In the measurements also such technical and physical factors as type of electrodes, frequency, geometry of the object, inter-electrode distance and temperature have an effect. These factors are discussed especially with respect to the impedance method in frost resistance studies of plants.

The PDF includes an abstract in Finnish.

  • Repo, E-mail: tr@mm.unknown (email)

Category : Research article

article id 10620, category Research article
Tapani Repo, Virva Volanen, Pertti Pulkkinen. (2022). No difference in the maximum frost hardiness of different pedunculate oak populations in Finland. Silva Fennica vol. 56 no. 2 article id 10620. https://doi.org/10.14214/sf.10620
Keywords: climate change; differential thermal analysis; electrolyte leakage; low-temperature exotherm; species distribution; visual damage scoring
Highlights: Four pedunculate oak populations were compared for their maximum frost hardiness (FHmax) at two sampling times in midwinter; Based on the initiation of the low temperature exotherm (LTE), FHmax was an average of –41 °C; Based on the relative electrolyte leakage method, FHmax was an average of –46 °C and –41 °C in the first and second sampling time respectively; No significant differences were observed among the populations; Within-population variation in the LTE was high, providing potential for breeding; In extreme winters, FHmax may be critical for the growth and survival of oak in central and northern Finland.
Abstract | Full text in HTML | Full text in PDF | Author Info

The natural northern distribution limit for pedunculate oak (Quercus robur L.) is in southern Finland. We hypothesized that the maximum frost hardiness (FHmax) in the winter limited the cultivation of oaks in northern latitudes. We tested the hypothesis with controlled freezing tests in midwinter. The acorns for the experiment were collected from the four main oak populations in southernmost Finland. The seedlings were raised in the nursery, frost hardened in field conditions, and then moved to a growth chamber at –2 °C on two occasions in winter and tested for FHmax in controlled freezing tests. Frost hardiness was assessed by differential thermal analysis (DTA) based on the low temperature exotherm (LTE) and relative electrolyte leakage (REL) of the stem, and visual damage scoring (VD) of the buds and stem. The initiation and peak of the LTE took place at an average of –41 °C and –43 °C respectively, without differences among the populations. The variation in the initiation and peak of the LTE was high, ranging from –34.6 °C to –45.5 °C and from –37.1 °C to –46.9 °C respectively. According to the REL method, the frost hardiness of the populations ranged from –44.0 °C to –46.4 °C in February and from –40.6 °C to –41.6 °C in March, without significant differences among the populations. According to VD, the bud was the least frost hardy organ, with FH between –19 °C and –33 °C, depending on population and assessment time. We conclude that the maximum hardiness may set the limit for the distribution of pedunculate oak northwards, but the high within-population variation offers potential to breed more frost hardy genotypes.

  • Repo, Natural Resources Institute Finland (Luke), Natural Resources, Yliopistokatu 6b, FI-80100 Joensuu, Finland ORCID https://orcid.org/0000-0002-7443-6275 E-mail: tapani.repo@luke.fi (email)
  • Volanen, Kalevankatu 4b B21, FI-80110 Joensuu, Finland E-mail: virva.volanen@siunsote.fi
  • Pulkkinen, Natural Resources Institute Finland (Luke), Production systems, Latokartanonkaari 9, FI-00790 Helsinki, Finland ORCID https://orcid.org/0000-0002-1643-7691 E-mail: pertti.pulkkinen@luke.fi
article id 208, category Research article
Mikko Räisänen, Tapani Repo, Tarja Lehto. (2009). Cold acclimation of Norway spruce roots and shoots after boron fertilization. Silva Fennica vol. 43 no. 2 article id 208. https://doi.org/10.14214/sf.208
Keywords: boron deficiency; dieback; freezing tolerance; mineral nutrition
Abstract | View details | Full text in PDF | Author Info
Boron deficiency, manifested as shoot dieback, is a problem in conifer stands growing on soils with high nitrogen availability in Fennoscandia. Earlier observations on Norway spruce (Picea abies L. Karst.) suggest that freezing tolerance is decreased by boron deficiency. Here, the effect of boron fertilization on cold acclimation of Norway spruce was studied in a young stand with initially low boron status two years after fertilization. Buds, stems, needles and roots were collected at five sampling times during cold acclimation and subsequently exposed to series of freezing temperatures. Lethal temperatures of organs were assessed by electrolyte leakage method (EL) and visual scoring of damage (VS). Freezing tolerance of buds was measured also by differential thermal analysis (DTA). The mean boron (B) concentration in needles was 4 mg kg–1 in unfertilized and 21 mg kg–1 in B-fertilized trees while critical level of B deficiency is considered to be 5 mg kg–1. The risk for increased freezing injuries in the low-B trees was not evident since all trees achieved cold hardiness that would be sufficient in central Finland. At two sampling times out of five, shoots or stem of B-fertilized trees were slightly more freezing tolerant than non-fertilized trees. However, the present study does not give strong evidence for the hypothesis that decreased freezing tolerance in B deficiency would be a triggering factor for leader dieback in Norway spruce at the B levels studied.
  • Räisänen, University of Joensuu, Faculty of Forest Sciences, P.O.Box 111, FI-80101 Joensuu, Finland; (present address), FAForest, FI-83480 Ahonkylä, Finland E-mail: mr@nn.fi (email)
  • Repo, Finnish Forest Research Institute, Joensuu Unit, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: tr@nn.fi
  • Lehto, University of Joensuu, Faculty of Forest Sciences, P.O.Box 111, FI-80101 Joensuu, Finland E-mail: tarja.lehto@joensuu.fi
article id 328, category Research article
Pedro J. Aphalo, Markku Lahti, Tarja Lehto, Tapani Repo, Aino Rummukainen, Hannu Mannerkoski, Leena Finér. (2006). Responses of silver birch saplings to low soil temperature. Silva Fennica vol. 40 no. 3 article id 328. https://doi.org/10.14214/sf.328
Keywords: biomass; Betula pendula; photosynthesis; electrical impedance; mineral nutrients; soil temperature; stomatal conductance; water relations
Abstract | View details | Full text in PDF | Author Info
Two-year-old silver birch (Betula pendula) saplings were grown for a third growing season in controlled-environment rooms (dasotrons) at three soil temperatures (5, 10, and 20 °C). All trees grew the first flush of leaves, but the growth of the second flush was almost completely inhibited at the two lower temperatures. The dry weight of the second-flush leaves was 50 times larger at 20 °C than at 5 and 10 °C, with about 100 times more nitrogen. Root growth was less affected than shoot growth. Chlorophyll content, net assimilation rate and stomatal conductance were lower at low soil temperatures. The value of the cytoplasm resistance estimated from the electric impedance spectra was lower at 5 °C than at 10 or 20 °C. Leaf water potential was highest at the lowest soil temperature, and intercellular carbon dioxide concentration was only slightly lower in saplings growing in cooler soil. We conclude that the effect of long-term exposure to cold soil on net assimilation and growth was not caused by stomatal closure alone. It is likely to be additionally mediated by the limited nitrogen acquisition at the low soil temperatures, and perhaps additionally by some other factor. As the growth depression of aboveground parts in response to low soil temperature was more significant in silver birch than what has earlier been found in conifers, the relative changes in air and soil temperature may eventually determine whether birch will become more dominant in boreal forests with climate change.
  • Aphalo, University of Helsinki, Department of Biological and Environmental Sciences E-mail: pja@nn.fi
  • Lahti, The Finnish Forest Research Institute E-mail: ml@nn.fi
  • Lehto, University of Joensuu, Faculty of Forestry, Box 111, FI-80101 Joensuu, Finland E-mail: tarja.lehto@joensuu.fi (email)
  • Repo, The Finnish Forest Research Institute E-mail: tr@nn.fi
  • Rummukainen, University of Joensuu, Faculty of Forestry, Box 111, FI-80101 Joensuu, Finland E-mail: ar@nn.fi
  • Mannerkoski, University of Joensuu, Faculty of Forestry, Box 111, FI-80101 Joensuu, Finland E-mail: hm@nn.fi
  • Finér, The Finnish Forest Research Institute E-mail: lf@nn.fi
article id 380, category Research article
Tapani Repo, Janne Laukkanen, Raimo Silvennoinen. (2005). Measurement of the tree root growth using electrical impedance spectroscopy. Silva Fennica vol. 39 no. 2 article id 380. https://doi.org/10.14214/sf.380
Keywords: willow; CNLS-curve fitting; displacement method; distributed electric model; hydroponics; impedance analysis
Abstract | View details | Full text in PDF | Author Info
The non-destructive evaluation of plant root growth is a challenge in root research. In the present study we aimed to develop electrical impedance spectroscopy (EIS) for that purpose. Willows (Salix myrsinifolia Salisb.) were grown from cuttings in a hydroponic culture in a growth chamber. Root growth was monitored at regular intervals by a displacement method and compared with the EIS parameters of the plants. To measure its impedance spectrum (IS) (frequency range from 40 Hz to 340 kHz) each plant was set in a measuring cell filled with a solution of the hydroponic culture. The IS was measured using a two-electrode measuring system. A silver needle electrode was connected to the stem immediately above the immersion level and a platinum wire was placed in the solution. The measurements were repeated twice weekly for a root growth period of one month. The IS of the entity consisting of a piece of stem, roots and culture solution were modelled by means of an electric circuit consisting of two ZARC-Cole elements, one constant-phase element, and a resistor. On the plant basis, an increase in root volume by growth correlated with a reduction in the sum of resistances in the ZARC-Cole elements (mean Pearson’s correlation coefficient r = –0.70).
  • Repo, The Finnish Forest Research Institute, Joensuu Research Centre, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: tapani.repo@metla.fi (email)
  • Laukkanen, University of Joensuu, Department of Physics, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: jl@nn.fi
  • Silvennoinen, University of Joensuu, Department of Physics, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: rs@nn.fi

Category : Research note

article id 608, category Research note
Jouni Partanen, Ilkka Leinonen, Tapani Repo. (2001). Effect of accumulated duration of the light period on bud burst in Norway spruce (Picea abies) of varying ages. Silva Fennica vol. 35 no. 1 article id 608. https://doi.org/10.14214/sf.608
Keywords: Norway spruce; phenology; growth initiation; photoperiod
Abstract | View details | Full text in PDF | Author Info
One-year-old seedlings (two sowing times), two-year-old seedlings and 14- and 18-year-old cuttings of Norway spruce (Picea abies (L.) Karst.) were exposed to shortening photoperiod (initially 16 h), lengthening photoperiod (initially 6 h) and constant short photoperiod (6 h) treatments with uniform temperature conditions in growth chambers. The timing of bud burst was examined. In all plants, shortening photoperiod treatment seemed to promote bud burst compared with other treatments. This effect was clearest in the oldest material. The results suggest that, in addition to temperature sum, the accumulated duration of the light period may promote bud burst of Norway spruce.
  • Partanen, Finnish Forest Research Institute, Punkaharju Research Station, Finlandiantie 18, FIN-58450 Punkaharju, Finland E-mail: jouni.partanen@metla.fi (email)
  • Leinonen, University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland E-mail: il@nn.fi
  • Repo, University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland E-mail: tr@nn.fi

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