sTREND - synthesis on tree Traits Response to Neighboring Diversity

sTREND stands for “synthesis on tree Traits REsponse to Neighborhood Diversity”. The novelty of sTREND lies in taking into account that in a diversified community, a plant’s heterospecific neighbours can modify its physical (e.g. shading) - chemical (e.g. VOC) environment and that this plant, because of its phenotypic plasticity, can respond to this altered environment by changing the expression of its functional traits, in turn modifying the biotic interactions and abiotic environment involved in the functioning of the whole plant community.

The specific scientific objectives of sTREND are

i) to identify the above- and belowground traits with the greatest plastic response to neighbour diversity and the tree species with greater trait plasticity

ii) to compare the effect of different neighbour diversity and spatial distribution metrics on this phenotypic response

iii) to test interactions between these neighbour effects and environmental conditions, particularly soil and climate conditions

iv) to infer theoretical consequences of the role of this feedback loop on the main ecological functions associated with the functional traits measured.

Finally, sTREND will see if it is possible to develop a new functional diversity index that takes into account the response of trees to neighbouring diversity, e.g. a functional plasticity index and test if the abundance of species with higher plasticity index is a good predictor of observed BEF relationships.

sTREND aims to compile all available data on a maximum number of functional traits measured in a standard way at a maximum number of TreeDivNet sites and characterising different parts of the tree, trunk (e.g. wood density), branches (e.g. crown width), leaves (e.g. SLA, C/N) and roots (e.g. specific root length). A preliminary survey has already revealed that at least 20 TreeDivNet experiments are willing to share data which cover at least two functional traits per experiment (often four to six) are distributed over temperate, boreal, Mediterranean and tropical biomes. These data will be analysed using multivariate statistical methods to compare contrasting situations (e.g. conspecific vs. heterospecific neighbourhood), interacting with environmental variables and taking into account correlations between traits (e.g. trade-offs). For traits that have been measured at least twice per site, sTREND will test the effect of tree age on the change in trait value as a function of neighbour diversity, in order to integrate the role of ontogeny and, for example, to understand why the effect of diversity on certain functions, such as primary productivity, increases over time. The results obtained will be highly relevant to a better understanding of the ecological mechanisms underlying the relationships between biodiversity, spatial heterogeneity, and forest functioning, particularly those involving the plastic response of functional traits to the diversity of neighbors in species-rich communities. From a more applied point of view, this information will also be relevant for identifying the species best able to adapt their functional traits in a context of high neighboring diversity, and thus informing managers on the best species composition for their mixed plantations.

Funding and Partners

The sTREND project is an sDiv synthesis working group, supported by iDiv (German Centre for Inegrative Biodiversity Research)

The principle investigators of sTrend are Hervé Jactel and Simone Mereu. Supporting iDiv members are Helge Bruelheide and Jens Kattge.