Effects of tree species diversity on resistance to biotic disturbances in planted forests

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1 Effects of tree species diversity on resistance to biotic disturbances in planted forests Hervé Jactel, Johana Boberg, Eckehard Brockerhoff, Bastien Castagneyrol, Julia Koricheva, Nicolas Meurisse

2 An urgent need for new, planted forests 1. to meet the social demand for wood products including energy wood 2. to contribute to climate change mitigation through carbon sequestration 3. to alleviate the logging pressure on natural forests and preserve biodiversity

3 Rising threats due to global change 1. Climate change temperatures trigger pest outbreaks and range expansion Pine processionary moth droughts increase tree susceptibility to infection

4 Rising threats due to global change 2. World trade Number new species / year globalization results in more biological invasions Exotic arthropods Dryocosmus kuriphilus Origine: China

5 Challenge: design new planted forests less vulnerable on the long term Trees are being planted for decades or centuries Trees will experience disturbances never met before

6 Is mixing tree species in planted forest an option? Diversity resistance relationships in grasslands

7 Is mixing tree species in planted forest an option? Evidence of multifunctionality in multiple species forests

8 Resistance of mixed forest to biotic disturbances - Pest insects - Fungal pathogens - Mammal herbivores 1. Patterns of response to tree diversity 2. Underlying ecological mechanisms 3. Recommendations to managers

9 + damage In mixed foersts damage In mixed forests Resistance of mixed forest to pest insects 119 case studies, 33 tree species Lower damage in mixed forests in 80% of the cases 36% decrease of damage for a tree species grown in mixed stands

10 Resistance of mixed forest to pest insects 15 tree species in 209 forests -31%

11 Resistance of mixed forest to fungal pathogens Overall better resistance of mixed forests to root rot fungi Armillaria Gerlach et al Heterobasidion Linden & Vollbrecht 2002

12 Resistance of mixed forest to fungal pathogens Resistance or neutral effects for foliar pathogens 209 forests Oïdium Hantsch et al. 2013

13 Resistance of mixed forest to mammal herbivores Contrasting effects on mammal herbivores

14 Resistance of mixed forest to mammal herbivores Contrasting effects on mammal herbivores Cook-Patton et al. 2014

15 Resistance of mixed forest: common features 1. Direction and magnitude of effects depend on pest specialization - 42% - 15% 0% Castagneyrol et al Spill over - Mixing diet

16 Resistance of mixed forest: common features 2. Forest composition > tree species richness % damage reduction conifer conifer broadl. broadl. broadl. conifer conifer broadl. 0% -10% -20% -30% -40% -50% -60% 27% 45%

17 Mechanisms underlying diversity resistance relationships 1. Reduced host tree density - less likely to enter the plot Tree mortality due to A. ostoyae in mixed stands - reduced residence time (OFT) - lower amount of resources - longer distance between host trees Gerlach et al. 1997

18 ORPHEE experiment

19 height P Bp pin en +P Qr pin ob +P Qp pin yr +P pi Qi n Qr le x ob + +P Ppi Qp pin n + yr +P Bpe Pp pin n + in +B Bpe pe n Qr n+ ob Qi +P l pi ex Qr ob n+q +Q py Qp ilex r Qr + ob yr+q Pp +P ile in p x+ Qr i P ob n+b p e p in +P n+ Pp pin +B Qp in yr +Q pe n p + Qr y Qr ob r+q Qile ob il x + +P Ppi ex+ n Bp pi n+ +Q en Qp ile x+ yr +Q Qp yr ile x+ Bp en % infested pines Mechanisms underlying diversity resistance relationships 2. Reduced probability of host tree being found 8% 7% 6% 5% 4% 3% 2% 1% 0% birch pine oak

20 Mechanisms underlying diversity resistance relationships 2. Reduced probability of host tree being consumed Spruce - Fir Browsing frequency Saplings planted under Eglantine Beech - Maple

21 Mechanisms underlying diversity resistance relationships Arthropod species Diversité spécifique richness des arthropodes 3. Reinforced biological control by natural enemies Herbivore Herbivore Pollinator Pollinisateur Prédateur Predator Détritivore Detritivore DiversitéPlant spécifique des plantes species richness

22 Mechanisms underlying diversity resistance relationships 3. Reinforced biological control by natural enemies Neodiprion sertifer 100% Scots pine 50% Scots pine 50% Birch

23 Mechanisms underlying diversity resistance relationships 3. Reinforced biological control by antagonists

24 Recommendations to forest managers 1. Mixing 2 species can be enough 2. Providing that they have contrasting traits 3. Favour conifer broadleaved mixtures

25 Recommendations to forest managers Mixing 2 species can be enough Providing that they have contrasting traits Favour conifer broadleaved mixtures 4. Two possible spatial configurations Strip pattern Edge pattern Letourneau et al. 2011

26 Thank you for your attention