Size inequality reduces
productivity in pure
forest stands
Thomas Bourdier, Thomas Cordonnier,
Georges Kunstler & Benoit Courbaud
Pour mieux
affirmer
ses missions,
le Cemagref
devient Irstea
www.irstea.fr
9th IUFRO International Conference on
Uneven‐aged Silviculture
June 19th 2014
2
Context
Growing interest in understanding the links between forest
structure and ecosystem services (Gamfeldt et al. 2013)
• Ecosysteme services = the benefits people obtain from
ecosystems (MEA,2005)
• Link with forest management: Which structures and species
mixing should we favour to maintain high level of ecosystem
services?
Production: ecosystem service with high economic value (France)
9th IUFRO
Conference
June 19th 2014
• Revenue: 40 billions € and 230 000 jobs
• Total: 58 Mm3 / year:
•
•
•
Timber wood 22 Mm3 / year
Wood for industry 12 Mm3 / year
Energy wood 24 Mm3 / year
3
Background
EFFECT OF STRUCTURE ON PRODUCTION
Effect of species diversity
• Increased production :
• when low productivity (Belote et al. 2011, Paquette & Messier 2011, Toigot in
prep.)
•
Mixing of trees with different functional characteristics (Kelty 1992, Pretzch
2005, Zhang et al. 2012, Vilà et al. 2013)
•
9th IUFRO
Conference
June 19th 2014
No effect or decreased production
• In mature forests (Long & Shaw 2010, Hardiman et al. 2011)
• Stands dominated by beech (Jacob et al. 2010)
Effect of size diversity
More ambiguous: some postive effects (Hardiman et al. 2011, Lei et al. 2009) and
no effect (Long & Shaw, 2010)
4
Aim of the study
Quantify the marginal effect of size heterogeneity on the
production of forest stands with regard to the functional
characteristics of the species
• Better qualify and quantify the effect of size heterogeneity in pure
forest stands of various species
• Determinate if species functional characteristics have an effect on
stand production
9th IUFRO
Conference
June 19th 2014
5
Hypotheses
EFFECT OF SIZE HETEROGENEITY ON PRODUCTION
Even-aged
Uneven-aged
Shade tolerant
species
Pure stands
Light demanding
species
same density and mean diameter
9th IUFRO
Conference
June 19th 2014
• Negative effect of size heterogeneity on stand production?
• Effect decreases with shade tolerance?
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Material & methods
THE FRENCH NATIONAL FOREST INVENTORY
Data from 2006 to 2011
•
•
•
44 000 plots available
Dendrometric and ecological data
Georeferenced: climatic data can
enhanced the plot information
Stand description
Flora inventory
Pure stands
•
•
>80% pure (basal area)
10 species studied
Soil characteristics
Tree measurement
9th IUFRO
Conference
June 19th 2014
Species
Nb plots
Scots sessile Peduncul maritime
Downy Silver Aleppo Norway
Beech
Larch
pine
oak
ate oak
pine
oak
fir
pine Spruce
1142
1082
870
860
813
667
421
252
232
152
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Material & methods
SIZE HETEROGENEITY INDEX: THE GINI COEFFICIENT
Index derived from the economy
•
•
•
Used in ecology since the 80’s (Weiner 1985, Geber 1989, Knox et al. 1989)
Better performance than other indices (Lexerod and Eid 2006, Valbuena et al. 2011)
Increasingly used: (Duduman, 2011; Klopcic and Boncina, 2011, Valbuena et al. 2011)
• Can be used with several species and in all forest stands
• Range from 0 perfect equality to
1 maximum theoritical inequality
•
In practice 0,1 to 0,7
9th IUFRO
Conference
June 19th 2014
• Gini = 2 x
8
GINI
Gini=0.2
Gini=0.35
Gini=0.55
Gini=0.7
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Material & methods
SHADE TOLERANCE INDEXES
Shade tolerance = capacity for growth in the shade (Niinemets &
Valladares, 2006)
We tested 2 indices:
• Ellenberg’s indicator values (1991)
•
•
•
From 3 to 9 for woody species
Developped for central Europe
Characterize species’ potential to grow in the understory
• Niinemets & Valladares (2006):
9th IUFRO
Conference
•
•
Index confined between 1 (very intolerant) and 5 (very tolerant)
Available for many species (806 worldwide)
June 19th 2014
Differences between deciduous and evergreen species? (Lusk et al. 2008)
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Material & methods
STAND PRODUCTIVITY: MODEL SELECTION
𝒅𝑮 =∝ 𝑮𝜷 𝒆𝜸𝑫𝒒 𝒆𝜹𝑮𝒊𝒏𝒊
G=basal area
Dq= mean quadratic diameter
Gini= Gini coefficient
α: site effect: 𝛼 = 𝑎0 + 𝑎1 𝑊𝐵 + 𝑎2 𝑠𝑔𝑑𝑑
WB= water budget
sgdd= sum of degree days
9th IUFRO
Conference
Model selection for each species to retain only the influent variables
June 19th 2014
What is the effect of the Gini coefficient on the forest stand
production?
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Effect of size heterogeneity on the production
of pure forest stands
Significant negative effect for 7 out of the 10 species studied
9th IUFRO
Conference
June 19th 2014
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Interaction between shade tolerance and size
heterogeneity
No clear interaction between species shade tolerance and Gini effect
No difference between deciduous and conifer trees
9th IUFRO
Conference
June 19th 2014
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Effect of size heterogeneity on the production
of pure forest stands
For most species, stands with low size heterogeneity are more
productive than stands with high size heterogeneity
Effect of size heterogeneity could not be related to shade
tolerance
• No effect of other traits (wood density, SLA)
2 Hypothetical mecanisms investigated:
9th IUFRO
Conference
June 19th 2014
• Light interception efficiency reduced by heterogeneity?
• Conversion efficiency reduced for largest trees?
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Experiments with a forest dynamics model
SAMSARA 2
3 species:
•
•
•
Norway spruce
Silver fir
European beech
FNI plots
Growth modelled
for 10 years
9th IUFRO
Conference
June 19th 2014
Variables:
•
•
•
Production
Courbaud et al. submitted
Light interception
Light conversion rate= plot production / plot intercepted light
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Simulation results
𝒅𝑮 =∝ 𝑮𝜷 𝒆𝜸𝑫𝒒 𝒆𝜹𝑮𝒊𝒏𝒊 𝒆𝜺𝒔𝒑𝒆𝒄𝒊𝒆𝒔
Negative effect of Gini on:
• Production (-0,556***)
• Light interception (-0,257***)
• Light conversion rate (-0,299***)
9th IUFRO
Conference
June 19th 2014
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Conclusion and perspectives
Convergence between empirical results and simulations
An increase of size heterogeneity decreases:
•
•
Efficiency in stand light interception
Efficiency in light conversion in growth
No clear differences between species
Static results: forest dynamic may affect our results
9th IUFRO
Conference
June 19th 2014
Size heterogeneity effect is influenced by ground slope?
Effect on volume instead of basal area?
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Questions??
Thank you for your attention
18
Effect of slope on the effect of Gini
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Model selection
Species
PinSyl
CheSes
ChePed
PinMar
Het
ChePub
Sap
PinAle
Epi
Mel
AIC comparison
Models with
Models
Gini
without Gini
1751
1757
931
947
769
798
720
791
969
990
822
820
517
519
351
353
230
231
240
238
Test
True
True
True
True
True
False
True
True
True
False
Anova
**
***
***
***
***
0,656
*
*
*
0,684
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Questions??
Thank you for your attention
21
Hypotheses
EFFECT OF SIZE HETEROGENEITY ON PRODUCTION
Even-aged
Uneven-aged
Shade tolerant
species
Pure stands
Light demanding
species
--
9th IUFRO
Conference
June 19th 2014
Mixed stands
same density and mean diameter