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

• Published in: PloS one 2016-03, Vol.11 (3), p.e0151852-e0151852
• Main Authors: Bourdier, Thomas, Cordonnier, Thomas, Kunstler, Georges, Piedallu, Christian, Lagarrigues, Guillaume, Courbaud, Benoit
• Format: Article
• Language: English
• Subjects: Abies alba; Abiotic factors; Analysis; Biodiversity; Biology and Life Sciences; Biomass; Community relations; Competition; Complementarity; Computer Simulation; Data processing; Developmental stages; Ecology and Environmental Sciences; Ecosystems; Efficiency; Environmental Sciences; Europe; Fagus sylvatica; Forest productivity; Forests; Inequality; Influence; Interception; Larix decidua; Light; Light interception; Mixed forests; Models, Biological; Picea abies; Pinus halepensis; Pinus pinaster; Pinus sylvestris; Plant communities; Plant diversity; Plant morphology; Plant populations; Productivity; Quercus petraea; Quercus pubescens; Quercus robur; Shade; Species diversity; Species Specificity; Tree growth; Trees; Trees - anatomy & histology; Trees - radiation effects
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0151852

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.