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Characterizing tropical tree species growth strategies: learning from inter-individual variability and scale invariance.

Le Bec J, Courbaud B, Le Moguédec G, Pélissier R - PLoS ONE (2015)

Bottom Line: We quantified both species responses to biotic and abiotic factors and individual tree effects unexplained by these factors.In addition, intraspecific variability increased as a power function of species maximum growth partly as a result of higher absolute responses of fast-growing species to competition and tree size.These results reflect a scale invariance of the growth process, underlining that slow- and fast-growing species exhibit the same range of growth strategies.

View Article: PubMed Central - PubMed

Affiliation: IRD, UMR AMAP, Montpellier, France; AgroParisTech, Paris, France.

ABSTRACT
Understanding how tropical tree species differ in their growth strategies is critical to predict forest dynamics and assess species coexistence. Although tree growth is highly variable in tropical forests, species maximum growth is often considered as a major axis synthesizing species strategies, with fast-growing pioneer and slow-growing shade tolerant species as emblematic representatives. We used a hierarchical linear mixed model and 21-years long tree diameter increment series in a monsoon forest of the Western Ghats, India, to characterize species growth strategies and question whether maximum growth summarizes these strategies. We quantified both species responses to biotic and abiotic factors and individual tree effects unexplained by these factors. Growth responses to competition and tree size appeared highly variable among species which led to reversals in performance ranking along those two gradients. However, species-specific responses largely overlapped due to large unexplained variability resulting mostly from inter-individual growth differences consistent over time. On average one-third of the variability captured by our model was explained by covariates. This emphasizes the high dimensionality of the tree growth process, i.e. the fact that trees differ in many dimensions (genetics, life history) influencing their growth response to environmental gradients, some being unmeasured or unmeasurable. In addition, intraspecific variability increased as a power function of species maximum growth partly as a result of higher absolute responses of fast-growing species to competition and tree size. However, covariates explained on average the same proportion of intraspecific variability for slow- and fast-growing species, which showed the same range of relative responses to competition and tree size. These results reflect a scale invariance of the growth process, underlining that slow- and fast-growing species exhibit the same range of growth strategies.

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Observed and fitted growth variability according to species maximum growth.Variance of observed growth within each species according to species maximum growth (A).Proportion of this intraspecific variability captured by the model for each species (Ri²) according to species maximum growth (B). The lines represent fitted relationships with a power (A) and a linear function (B).
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pone.0117028.g003: Observed and fitted growth variability according to species maximum growth.Variance of observed growth within each species according to species maximum growth (A).Proportion of this intraspecific variability captured by the model for each species (Ri²) according to species maximum growth (B). The lines represent fitted relationships with a power (A) and a linear function (B).

Mentions: Observed intraspecific growth variability, σi²(Δdbhijt), widely differed among species and increased significantly as a power function of species maximum growth (Fig. 3A). The proportion of this variability captured by the model (Ri²) was on average 63% ± 11% (up to 80% for some fast-growing species) and also increased significantly with species maximum growth (Fig. 3B).


Characterizing tropical tree species growth strategies: learning from inter-individual variability and scale invariance.

Le Bec J, Courbaud B, Le Moguédec G, Pélissier R - PLoS ONE (2015)

Observed and fitted growth variability according to species maximum growth.Variance of observed growth within each species according to species maximum growth (A).Proportion of this intraspecific variability captured by the model for each species (Ri²) according to species maximum growth (B). The lines represent fitted relationships with a power (A) and a linear function (B).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355905&req=5

pone.0117028.g003: Observed and fitted growth variability according to species maximum growth.Variance of observed growth within each species according to species maximum growth (A).Proportion of this intraspecific variability captured by the model for each species (Ri²) according to species maximum growth (B). The lines represent fitted relationships with a power (A) and a linear function (B).
Mentions: Observed intraspecific growth variability, σi²(Δdbhijt), widely differed among species and increased significantly as a power function of species maximum growth (Fig. 3A). The proportion of this variability captured by the model (Ri²) was on average 63% ± 11% (up to 80% for some fast-growing species) and also increased significantly with species maximum growth (Fig. 3B).

Bottom Line: We quantified both species responses to biotic and abiotic factors and individual tree effects unexplained by these factors.In addition, intraspecific variability increased as a power function of species maximum growth partly as a result of higher absolute responses of fast-growing species to competition and tree size.These results reflect a scale invariance of the growth process, underlining that slow- and fast-growing species exhibit the same range of growth strategies.

View Article: PubMed Central - PubMed

Affiliation: IRD, UMR AMAP, Montpellier, France; AgroParisTech, Paris, France.

ABSTRACT
Understanding how tropical tree species differ in their growth strategies is critical to predict forest dynamics and assess species coexistence. Although tree growth is highly variable in tropical forests, species maximum growth is often considered as a major axis synthesizing species strategies, with fast-growing pioneer and slow-growing shade tolerant species as emblematic representatives. We used a hierarchical linear mixed model and 21-years long tree diameter increment series in a monsoon forest of the Western Ghats, India, to characterize species growth strategies and question whether maximum growth summarizes these strategies. We quantified both species responses to biotic and abiotic factors and individual tree effects unexplained by these factors. Growth responses to competition and tree size appeared highly variable among species which led to reversals in performance ranking along those two gradients. However, species-specific responses largely overlapped due to large unexplained variability resulting mostly from inter-individual growth differences consistent over time. On average one-third of the variability captured by our model was explained by covariates. This emphasizes the high dimensionality of the tree growth process, i.e. the fact that trees differ in many dimensions (genetics, life history) influencing their growth response to environmental gradients, some being unmeasured or unmeasurable. In addition, intraspecific variability increased as a power function of species maximum growth partly as a result of higher absolute responses of fast-growing species to competition and tree size. However, covariates explained on average the same proportion of intraspecific variability for slow- and fast-growing species, which showed the same range of relative responses to competition and tree size. These results reflect a scale invariance of the growth process, underlining that slow- and fast-growing species exhibit the same range of growth strategies.

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