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Articles by Claes Hellqvist

Category: Research article

article id 7751, category Research article
Göran Nordlander, Euan G. Mason, Karin Hjelm, Henrik Nordenhem, Claes Hellqvist. (2017). Influence of climate and forest management on damage risk by the pine weevil Hylobius abietis in northern Sweden. Silva Fennica vol. 51 no. 5 article id 7751. https://doi.org/10.14214/sf.7751
Highlights: Analysis of survey data from 292 reforestation areas in northern Sweden show that the probability of pine weevil damage can be predicted with a standard error of 0.12; Three variables are important in the optimal model: proportion of seedlings in mineral soil, age of clear-cut, and temperature sum; Temperature sum in the model can be adjusted to reflect future climate scenarios.

The pine weevil Hylobius abietis L. is an economically important pest insect that kills high proportions of conifer seedlings in reforestation areas. It is present in conifer forests all over Europe but weevil abundance and risk for damage varies considerably between areas. This study aimed to obtain a useful model for predicting damage risks by analyzing survey data from 292 regular forest plantations in northern Sweden. A model of pine weevil attack was constructed using various site characteristics, including both climatic factors and factors related to forest management activities. The optimal model was rather imprecise but showed that the risk of pine weevil attack can be predicted approximatively with three principal variables: 1) the proportion of seedlings expected to be planted in mineral soil rather than soil covered with duff and debris, 2) age of clear-cut at the time of planting, and 3) calculated temperature sum at the location. The model was constructed using long-run average temperature sums for epoch 2010, and so effects of climate change can be inferred from the model by adjustment to future epochs. Increased damage risks with a warmer climate are strongly indicated by the model. Effects of a warmer climate on the geographical distribution and abundance of the pine weevil are also discussed. The new tool to better estimate the risk of damage should provide a basis for foresters in their choice of countermeasures against pine weevil damage in northern Europe.

  • Nordlander, Swedish University of Agricultural Sciences (SLU), Department of Ecology, P.O. Box 7044, SE-750 07 Uppsala, Sweden ORCID ID:E-mail: Goran.Nordlander@slu.se
  • Mason, University of Canterbury, School of Forestry, Private Bag 4800, Christchurch 8140, New Zealand; Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden ORCID ID: http://orcid.org/0000-0001-9024-9106 E-mail: euan.mason@canterbury.ac.nz (email)
  • Hjelm, Skogforsk, The Forest Research Institute of Sweden, Ekebo 2250, SE-268 90 Svalöv, Sweden; Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden ORCID ID:E-mail: karin.hjelm@skogforsk.se
  • Nordenhem, Swedish University of Agricultural Sciences (SLU), Department of Ecology, P.O. Box 7044, SE-750 07 Uppsala, Sweden ORCID ID:E-mail: h.nordenhem@telia.com
  • Hellqvist, Swedish University of Agricultural Sciences (SLU), Department of Ecology, P.O. Box 7044, SE-750 07 Uppsala, Sweden ORCID ID:E-mail: Claes.Hellqvist@slu.se
article id 432, category Research article
Bo Långström, Claes Hellqvist, Jan Cedervind. (2004). Comparison of methods for estimation of needle losses in Scots pine following defoliation by Bupalus piniaria. Silva Fennica vol. 38 no. 1 article id 432. https://doi.org/10.14214/sf.432
In 1996, ca. 7000 hectares of pine forests at Hökensås in SW Sweden were defoliated by the pine looper, Bupalus piniara (L.) (Lepidoptera. Geometridae). Following an aerial damage survey using CIR (colour infra red) photography, and estimation of pupal densities in the soil, ca 4000 ha of the most defoliated pine stands were sprayed in early August 1997 with Bacillus thuringiensis var. kurstaki. The control operation was succeessful but probably redundant, as no further defoliation occurred in unsprayed reference areas. In order to assess defoliation levels in different damage classes for later growth loss studies, 47 circular study plots were laid out in pine stands representing different damage and age classes. The remaining foliage was recorded for each tree using the following classes: 0, 10, 30, 50, 70, 90 and 100%. The defoliation levels in 1996 were estimated by disregarding the 1997 needle age class. Thirteen ca. 40-year-old sample trees representing different damage classes were felled, and the remaining foliage of all branches was estimated by needle age class using the above-mentioned scale. One branch in each of the whorls 1996, 1991, 1986 and 1981 was sampled and its needle dry weight was determined. The sample branch data confirmed the field observations that virtually no additional defoliation took place in 1997. The damage classes estimated from the CIR-pictures only agreed with the field damage estimates at the higher end of the damage scale. In contrast, the field estimate correlated well with plot means derived from tree-wise estimates (R2 = 0.93), and with with the calculated needle biomasses per tree (R2 = 0.90). Thus, the field damage classification was supported by the more detailed defoliation estimates, and hence forms a relevant basis for later growth loss studies.
  • Långström, SLU, Dept. of Entomology, P.O.Box 7044, S-750 07 Uppsala, Sweden. Fax +46 18 672 890 ORCID ID:E-mail: bo.langstrom@entom.slu.se (email)
  • Hellqvist, SLU, Dept. of Entomology, P.O.Box 7044, S-750 07 Uppsala, Sweden. Fax +46 18 672 890 ORCID ID:E-mail:
  • Cedervind, SLU, Dept. of Entomology, P.O.Box 7044, S-750 07 Uppsala, Sweden. Fax +46 18 672 890 ORCID ID:E-mail:

Category: Article

article id 5450, category Article
Bo Långström, Claes Hellqvist. (1991). Shoot damage and growth losses following three years of Tomicus-attacks in Scots pine stands close to a timber storage site. Silva Fennica vol. 25 no. 3 article id 5450. https://doi.org/10.14214/sf.a15604

Shoot losses due to maturation feeding by pine shoot beetles (Tomicus piniperda (L.) and T. minor (Hart.), Col., Scolytidae) and subsequent growth losses were studied in Scots pine (Pinus sylvestris L.) stands growing at different distances from a timber yard, where pine timber was stored during the years 1982–84. In autumn 1985, pine trees were felled at 20, 40, 80, 500 and 1,500 m distance from the timber yard, five trees in each distance class. Trees were analysed for beetle attack, needle biomass and growth. In autumn 1988, increment cores were taken from 20 trees in each distance class.

In 1985, different damage estimates showed that beetle damage was more than 10-fold in the crowns of pine trees growing close to the timber yard as compared to less damaged trees in greater distance. Crude needle biomass estimates indicated that the trees attacked most had lost more than half of the total foliage. Following three years of attack, basal area growth decreased for 2–3 years and recovered during the subsequent 3 years, the total period of loss thus being 5–6 years. The loss in volume growth during 1983–85 was ca. 70, 40, 20 and 10% at 20, 40, 80 and 500 m distance from the beetle source, respectively, compared to the stand at 1,500. Growth losses did not occur until the number of beetle-attacks, ”pegs”, exceeded ca. 200 per tree. The highest observed growth losses occurred in trees with more than 1,000 pegs per tree.

The PDF includes an abstract in Finnish

  • Långström, ORCID ID:E-mail:
  • Hellqvist, ORCID ID:E-mail:

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