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Effects of new forest management on insect damage risk in a changing
climate
Björkman, C., Bylund, H., Nilsson, U., Nordlander, G. and Schroeder, M.
Based on a book chapter manuscript for ”Climate Change and Insect Pests” Editors - C. Björkman and P. Niemelä.
Swedish University of Agricultural Sciences
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Insect forest pests
• Bark beetles – the spruce bark beetle (Ips typographus)
• Regeneration pests-the pine weevil (Hylobius abietis)
• Defoliators – several species
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Defoliators
Conifers
• Neodiprion sertifer – the European pine sawfly
• Diprion pini - the large pine sawfly
• Bupalus piniarus – the pine looper moth
• Lymantria monacha- the nun moth
• Dendrolimus pini – the pine tree lappet moth
• Panolis flammea – the pine beauty moth
Deciduous trees
• Operophtera spp. – the winter moth, geometrids
• Tortrix viridiana – the European leaf roller
• Lymantria dispar – the gypsy moth
• Zeiraphera griseana- the larch tortrix
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Climate warming and forest insect pests?
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Anticipated effects of climate change
Insects are ectotherms. In northern areas they are in general expected to respond positively to increased
temperature within a certain temperature range.
Natural enemies
Host plant
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Climate warming and bark beetles
• Shorter development time
• Increased number of generations
• Storm fellings – warmer winters
• Drought events
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Climate warming and the pine weevil
• Shorter development time and generation time
• Larger fraction of weevils overwintering as adults in the soil – feeding during autumn
• Longer growing seasons – increased feeding damage in plantations
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Climate warming and forest defoliators
• Shorter development time but not generation time
• Distribution and outbreak range will change
• Individualistic response of each species with potential changes in outbreak frequencies and population dynamics (cyclicity).
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Forest management types reviewed
Replacing even-aged spruce dominated forest in southern Fennoscandia.
Continuous cover forestry: no clear-felling
Mixed forests: spruce – birch and other species
Short rotation forestry: no thinning
Exotic tree species:
Conventional management: Even-aged stands, thinned 2-3 times before final clearfelling.
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Continuous cover forestry The spruce bark beetle
• Storm damage? -/+
• Mature trees always present but with larger gaps – reduced risk?
• Natural enemies higher abundance ? – reduced risk
• Transition period - important to consider ?
The large pine weevil
• Less breeding material – fewer stumps- reduced risk
• Natural regeneration – reduced risk
• More or less shaded stumps – reduced risk
• More scattered breeding substrate
Defoliators
• Trees of different age and size- differences in food quality –reduced risk
• Natural enemies- higher diversity and abundance? –reduced risk
• Not much known !?
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Mixed forests The spruce bark beetle
• Non-linear relationship spruce ratio and damage risk reduced risk -
• Storm damage ? +/-
• More scattered suitable host trees - reduced risk
The large pine weevil
• Less breeding material – reduced risk
• Less attraction to clear-cut areas? Reduced risk -?
Defoliators
• Tree species composition & specialist or generalist defoliators ?
• Natural enemies- higher diversity and abundance? Reduced risk
• Different consequences for conifer and deciduous trees
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Short rotation forestry- no thinning
The spruce bark beetle
• Fewer stands with suitable stem diameter – reduced risk
• Storm damage +/- ?
The large pine weevil
• Increased densities – more breeding substrate - increased risk +
• Planted regeneration – increased risk +
Defoliators
• Age class more important in some defoliator species +/- ?
• Age class could affect tree recovery/mortality rate -/+ ?
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Exotic tree species The spruce bark beetle
• Depends on tree species – able to reproduce in North American spruce species +/-
The large pine weevil
• Depends on tree species – if suitable breeding substrate +/-
• Planted regeneration – pine weevils are not picky: increased risk +?
Defoliators
• Depends on tree species – taxonomic affinity
Invasive species!
Chestnut leaf miner Cameraria ohridella
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Continuous cover
forestry
Mixed forest
Short rotation No thinning
Exotic tree species
Pine weevil Defoliators Spruce bark beetle
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Conclusion
Large knowledge gaps both effects of climate change and forest management on insect damage risks More research needed
• Field experiments & modelling more collaboration between entomology and silviculture researchers
• Combining data at different spatial scalelandscape perspective
• Invasive species
Can choice of forest management method mitigate risk of insect damage in a warming climate?
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Thank you for your attention!