Size inequality reduces productivity in pure forest stands
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Transcript of Size inequality reduces productivity in pure forest stands
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Thomas Bourdier, Thomas Cordonnier, Georges Kunstler & Benoit Courbaud
9th IUFRO International Conference on Uneven‐aged Silviculture
June 19th 2014
Size inequality reduces productivity in pure forest stands
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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)• 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
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June 19th 2014
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BackgroundEFFECT 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)
• 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 diversityMore ambiguous: some postive effects (Hardiman et al. 2011, Lei et al. 2009) and no effect (Long & Shaw, 2010)
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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
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Shade tolerant species
Light demanding species
Pure stands
Uneven-agedEven-aged
same density and mean diameter
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HypothesesEFFECT OF SIZE HETEROGENEITY ON PRODUCTION
Negative effect of size heterogeneity on stand production?
Effect decreases with shade tolerance?
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Material & methodsTHE 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
Pure stands• >80% pure (basal area)• 10 species studied
Stand description Flora inventory
Soil characteristics Tree measurement
Species Scots pine
sessile oak
Pedunculate oak
maritimepine Beech Downy
oakSilver
firAleppo
pineNorwaySpruce Larch
Nb plots 1142 1082 870 860 813 667 421 252 232 152
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June 19th 2014
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Material & methodsSIZE 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
• Gini = 2 x9th IUFRO
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GINI
Gini=0.2 Gini=0.35
Gini=0.55 Gini=0.7
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Material & methodsSHADE 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):• Index confined between 1 (very intolerant) and 5 (very tolerant)• Available for many species (806 worldwide)
Differences between deciduous and evergreen species? (Lusk et al. 2008)
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Material & methodsSTAND PRODUCTIVITY: MODEL SELECTION
G=basal area
Dq= mean quadratic diameter
Gini= Gini coefficient
α: site effectWB= water budget
sgdd= sum of degree days
Model selection for each species to retain only the influent variables
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
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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
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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:• Light interception efficiency reduced by heterogeneity?• Conversion efficiency reduced for largest trees? 9th IUFRO
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Experiments with a forest dynamics modelSAMSARA 2
3 species:• Norway spruce• Silver fir• European beech
FNI plots
Growth modelled
for 10 years
Variables:• Production• Light interception• Light conversion rate= plot production / plot intercepted light
Courbaud et al. submitted
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Simulation results
Negative effect of Gini on:• Production (-0,556***)• Light interception (-0,257***)• Light conversion rate (-0,299***)
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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
Size heterogeneity effect is influenced by ground slope?
Effect on volume instead of basal area?
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Thank you for your attention
Questions??
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Effect of slope on the effect of Gini
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Model selection
Models with Gini
Models without Gini
Test
PinSyl 1751 1757 True **CheSes 931 947 True ***ChePed 769 798 True ***PinMar 720 791 True ***Het 969 990 True ***ChePub 822 820 False 0,656Sap 517 519 True *PinAle 351 353 True *Epi 230 231 True *Mel 240 238 False 0,684
AIC comparisonAnovaSpecies
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Thank you for your attention
Questions??
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Shade tolerant species
Light demanding species
Pure stands
Mixed stands
Uneven-agedEven-aged
same density and mean diameter
--9th IUFRO Conference
June 19th 2014
HypothesesEFFECT OF SIZE HETEROGENEITY ON PRODUCTION