Observed and fitted growth variability according to species maximum growth.

<p>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 (R_i²) according to species maximum growth (B). The lines represent fitted relationships with a power (A) and a linear function (B).</p

Predicted species growth response shapes and amplitudes to competition, tree size and aspect.

<p>Predicted growth at standardized conditions with respect to competition (A), tree size (B) and aspect (C), i.e. with the other covariates fixed at their observed means. The 6 most abundant species are in bold in top panels. Bottom panels represent the distribution of species signed sensitivity to covariates, as defined in section Analysis.</p

Species absolute and relative sensitivities to competition and tree size according to species maximum growth.

<p>Species growth sensitivity to competition (A) and tree size (B) with respect to species maximum growth. Sensitivity was estimated as the range of predicted diameter increments (as defined in Materials and Methods). In top panels, sensitivity is considered in absolute values (i.e., in cm.yr⁻¹), while in bottom panels it is given in proportion of maximum predicted growth (in %).</p

Effect of Gini coefficient (δ from Eq 3) on productivity (dG).

<p>The results are presented according to species sensitivity to size heterogeneity (A) or to their shade tolerance (B). <i>Pinus Pinaster</i> was removed from (B) because there is no shade tolerance value in Niinemets & Valladeres (2006). Levels of significance are indicated on the graph based on a log-likelihood ratio test: (.) <i>p</i>-value <0.1, (*)<0.05, (**)<0.01, (***)<0.001. <i>p</i>-values are available in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151852#pone.0151852.s003" target="_blank">S3 Appendix</a> for all variables.</p

Characteristics of the plots for the ten species studied.

<p>Characteristics of the plots for the ten species studied.</p

Tree Size Inequality Reduces Forest Productivity: An Analysis Combining Inventory Data for Ten European Species and a Light Competition Model

<div><p>Plant structural diversity is usually considered as beneficial for ecosystem functioning. For instance, numerous studies have reported positive species diversity-productivity relationships in plant communities. However, other aspects of structural diversity such as individual size inequality have been far less investigated. In forests, tree size inequality impacts directly tree growth and asymmetric competition, but consequences on forest productivity are still indeterminate. In addition, the effect of tree size inequality on productivity is likely to vary with species shade-tolerance, a key ecological characteristic controlling asymmetric competition and light resource acquisition. Using plot data from the French National Geographic Agency, we studied the response of stand productivity to size inequality for ten forest species differing in shade tolerance. We fitted a basal area stand production model that included abiotic factors, stand density, stand development stage and a tree size inequality index. Then, using a forest dynamics model we explored whether mechanisms of light interception and light use efficiency could explain the tree size inequality effect observed for three of the ten species studied. Size inequality negatively affected basal area increment for seven out of the ten species investigated. However, this effect was not related to the shade tolerance of these species. According to the model simulations, the negative tree size inequality effect could result both from reduced total stand light interception and reduced light use efficiency. Our results demonstrate that negative relationships between size inequality and productivity may be the rule in tree populations. The lack of effect of shade tolerance indicates compensatory mechanisms between effect on light availability and response to light availability. Such a pattern deserves further investigations for mixed forests where complementarity effects between species are involved. When studying the effect of structural diversity on ecosystem productivity, tree size inequality is a major facet that should be taken into account.</p></div

Lorenz curve to calculate the Gini coefficient index for 4 different inventory plots.

<p>The Gini coefficient values are presented in the title of each facet. Trees are ranked according to their size (in our case individual tree basal area) in a descending order (according to Valbuena <i>et al</i>. 2013 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151852#pone.0151852.ref049" target="_blank">49</a>]). The dashed lines represent the line of absolute equality.</p

Results from Samsara2 simulations.

<p>Production in basal area (dG/dt), production in volume (dV/dt), total light interception (LIE), and light conversion rate (LUE) for <i>Fagus sylvatica</i>, <i>Picea abies</i> and <i>Abies alba</i>. Error bars indicate the confidence interval of δ for each variable represented.</p

Appendix A. Prior distributions, conditional relationships and distribution theory needed for algorithm development, algorithms used for Metropolis within Gibbs, and some issues related to MCMC diagnostics.

Prior distributions, conditional relationships and distribution theory needed for algorithm development, algorithms used for Metropolis within Gibbs, and some issues related to MCMC diagnostics

Appendix B. Parameter estimates, by species.

Parameter estimates, by species