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

Insect forest pests

• Bark beetles – the spruce bark beetle (Ips typographus)

• Regeneration pests-the pine weevil (Hylobius abietis)

• Defoliators – several species

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

Climate warming and forest insect pests?

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

Climate warming and bark beetles

• Shorter development time

• Increased number of generations

• Storm fellings – warmer winters

• Drought events

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

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).

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.

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 !?

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

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 -/+ ?

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

Continuous cover

forestry

Mixed forest

Short rotation No thinning

Exotic tree species

Pine weevil Defoliators Spruce bark beetle

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?

Thank you for your attention!