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Submitted on 5 Jun 2020
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Les forêts mélangées en Europe sont-elles plus résistantes aux sécheresses que les forêts pures?
Damien Bonal, Charlotte Grossiord, Arthur Gessler, André Granier
To cite this version:
Damien Bonal, Charlotte Grossiord, Arthur Gessler, André Granier. Les forêts mélangées en Europe sont-elles plus résistantes aux sécheresses que les forêts pures?. Séminaire IRSTEA, Jun 2015, Nogent sur Vernisson, France. �hal-01269057�
Tree diversity does not always improve resistance of forest ecosystems to drought
Damien BONAL
Charlotte GROSSIORD Arthur GESSLER
André GRANIER
Biomass Production
Loreau et al. 2001
Increasing species diversity can lead to important benefits for ecosystems
2
Higher biomass production in more diverse ecosystems
www.cedarcreek.umn.edu
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Biodiversity & Ecosystem functioning
Hantsch et al. 2013
Increasing species diversity can lead to important benefits for ecosystems
3
Lower foliar pathogen load in more diverse ecosystems
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www.bbc.co.uk www.worldofstock.com
Biodiversity & Ecosystem functioning
Resistance against pest &
pathogen outbreaks
Tilman & Downing 1994
Increasing drought resistance in more diverse communities
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4
Biodiversity & Ecosystem functioning
Are more diverse ecosystems more resistant to drought?
Stability against climatic perturbations
EEA, 2012
5
Species interactions can shift from negative (competition) to positive (complementarity) as climatic conditions change
(Stressgradient hypothesis, Bertness & Callaway, 1994)
Jucker & Coomes, 2012
Influence of environmental conditions
6
Test whether higher tree species diversity in forest ecosystems across Europe is associated with less drought exposure
www.nature.com Grossiord C.
Objectives
Casalegno et al. 2011
6 regions across North South gradient in Europe to cover the major forest types and climatic conditions
BOREAL (Finland)
HEMIBOREAL (Poland) TEMPERATE (Germany)
THERMOPHILOUS DECIDUOUS (Italy) MEDITERRANEAN (Spain)
MOUNTAINOUS TEMPERATE (Romania)
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Study Sites
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Comparison of ecosystem functioning for different levels of species mixture (15)
Tree species diversity
monoculture
monoculture
2sp mixture 3sp mixture
. . . . . . . . . .
Material and Methods
9
Material and Methods
• Selection of 25 to 42 stands (30×30m) varying in species richness in each studied region
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The variation in other confounding factors (soil, topography, land use history,…) was kept at a minimum.‐
Stands with varying tree species richness
0 10 20 30 40 50
Boreal Hemi-boreal Beech Moutainous beech Thermophilous
deciduous Mediterranean
Number of forest stands
5-species mixtures 4-species mixtures 3-species mixtures 2-species mixtures Monocultures
Temperate Mountainous temperate
Material and Methods
11
Material and Methods
• Selection of 25 to 42 stands (30×30m) varying in species richness in each studied region
• Extraction of wood cores from a selection of dominant and co
dominant trees of each species in each stand
C. Grossiord
6 trees in monoculture 3 trees/species in
mixtures
12
Material and Methods
• Selection of 25 to 42 stands (30×30m) varying in species richness in each studied region
• Extraction of wood cores from a selection of dominant and co
dominant trees of each species in each stand
• Selection of years (tree rings) with contrasting climatic conditions (dry vs. wet)
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Selection of the driest and the wettest year over the last 15 years with
daily climate data and the BILJOU waterbalance model (Granier et al. 1999):
0.0 0.2 0.4 0.6 0.8 1.0
0 20 40 60
Soil relative extractable water
Water stress index
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Example of Finland
Selection of years with contrasted climatic conditions
Material and Methods
14
Material and Methods
• Selection of 25 to 42 stands (30×30m) varying in species richness in each studied region
• Extraction of wood cores from a selection of dominant and co
dominant trees of each species in each stand
• Selection of years (tree rings) with contrasting climatic conditions (dry vs. wet)
• Analyses of carbon isotope composition ( 13C)δ
15
For each core, we extracted the late wood from the two selected years
Samples were then analyzed for carbon isotope composition (δ13C, ‰) (PTEF nancy or UC Davis)
Sample preparation and analyses
Material and Methods
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Material and Methods
• Selection of 25 to 42 stands (30×30m) varying in species richness in each studied region
• Extraction of wood cores from a selection of dominant and co
dominant trees of each species in each stand
• Selection of years (tree rings) with contrasting climatic conditions (dry vs. wet)
• Analyses of carbon isotope composition ( 13C) of latewood of δ each ring
• Calculation of plotlevel 13Cδ
Saurer et al. 1995
Decreasing water availability
Less negative δ13C values
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δ13C DRY δ13C WET
Material and Methods
• The difference in plotlevel 13C between the δ DRY and the WET year can be used as a proxy of drought exposure
If difference in δ13C is high, low resistance If difference in δ13C is low, high resistance
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Results
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = -0.4058x + 1.4461 R² = 0.2518
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = 0.681x + 1.0321 R² = 0.233
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = -0.5354x + 1.7015 R² = 0.2053
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = -0.50x +1.70 R2= 0.20 P= 0.007 Thermophilous deciduous
Hemi-boreal
Mountainous beech
Shannon diversity index
Increasein stand-levelδ13Cbetweena wetand a dry year(‰)
y = -0.40x + 1.44 R2= 0.25 P= 0.003 Temperate beech
Mediterranean
P= 0.159
P= 0.297
P= 0.716
Boreal y = 0.69x + 1.04
R2= 0.23 P= 0.038
Increasing diversity
Increasing drought exposure
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Results
Increasing diversity
Increasing drought exposureIncreasing drought exposure
δ13C values in DRY year always higher than in WET ones
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = -0.4058x + 1.4461 R² = 0.2518
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = 0.681x + 1.0321 R² = 0.233
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = -0.5354x + 1.7015 R² = 0.2053
0 1 2 3 4
0.0 0.5 1.0 1.5 2.0 2.5
y = -0.50x +1.70 R2= 0.20 P= 0.007 Thermophilous deciduous
Hemi-boreal
Mountainous beech
Shannon diversity index
Increasein stand-levelδ13Cbetweena wetand a dry year(‰)
y = -0.40x + 1.44 R2= 0.25 P= 0.003 Temperate beech
Mediterranean
P= 0.159
P= 0.297
P= 0.716
Boreal y = 0.69x + 1.04
R2= 0.23 P= 0.038
Increasing diversity
Increasing drought exposure
20
Results
Increasing diversity
Increasing drought exposureIncreasing drought exposure
Lower drought resistance in speciesrich forests
No effect of species diversity
Higher drought
resistance in speciesrich forests
Tree species diversity effects seem partially dependent on climatic
conditions
Rare events and low intensity of drought Negative effects
Frequent events and high intensity of drought
Positive effects 21
Abiotic conditions (e.g. soil type) Biotic conditions
(e.g. tree species composition)
Results
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• Tree species diversity influences the functioning of forest ecosystems in terms of water and carbon acquisition and use
• More diverse forests may be more resistant to soil drought than pure ones, but not necessarily
• Favoring mixed forest ecosystems could be preferred in certain regions, not only to preserve biodiversity or sustain productivity in the context of climate changes, but also to delay the negative effect of drought
Conclusions
Perspectives
23
Thanks for your attention
