Are positive diversity-production relationships mediated by root interactions ? A study with different forest mixtures.

PI : Catherine Collet (UMR 1092  Joint Research Unit for Forest and Wood Resource Studies – LEFORB)

Co-applicants : Damien Bonal, Marie-Béatrice Triboulot (EEF), Laurent Saint-André (BEF)

Collaboration :  Quentin Ponette (UCL, Belgique)

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Context — Over the past decades, many studies provided evidence that biodiversity enhances ecosystem functioning and ecosystem services. In forestry, studies show an overall positive effect of species diversity on forest productivity. To comply with this paradigm, forest management policies in many regions of the world presently aim at promoting mixed species forests and benefiting from the many ecological and economic advantages of mixed stands not provided by monocultures.

Objectives — To analyse whether complementarity for the use of belowground resource (water and nutrients) among tree species occurs and explains the observed higher productivity of mixed species stands.

Approach — An experimental approach is implemented, based on two experimental set-ups: a 15-year-old mixed Fagus–Acer plantation where both tree density and mixture vary, located in Lorraine France, and a series of Fagus–Quercus-Betula-Carpinus plots sampled in an observational biodiversity platform in the Belgian Ardenne.

In each setup, complementarity for belowground resource will be assessed by characterising belowground resource distribution, root system spatial arrangement, and water and nutrient acquisition, using innovative experimental and analytical methods to characterise root competition: (1) Implement near-infrared reflectance spectroscopy method to estimate the specific composition of root samples; (2) Use inverse modelling to estimate root distribution; (3) Use stable isotope tracers to estimate resource uptake by individual trees; (4) Use neighbourhood models to predict tree growth from resource availability and resource partitioning among competing trees.

Expected results and impacts — We are aiming for a better understanding of the processes that occur at the root-soil interface in mixed-species stands, in order to characterise and predict competition for belowground resources among tree species. Models allow us to predict important changes in the availability of belowground resources in European forests and a deeper understanding of the process that determine belowground resource partitioning among competing trees which is necessary to evaluate how mixed forests may adapt to future climatic and soil conditions.