Functional significance of tree species diversity for soil C, N and pH under major European forest types

Seid Muhie Dawud1, Karsten Raulund-Rasmussen1, Lars Vesterdal1
1 Department of Geosciences and Natural Resource Management (IGN), University of Copenhagen

O 5.4 in Linking biodiversity and biogeochemistry

15.07.2014, 12:00-12:20, H19

Functional significance of tree species diversity and identity for soil C, N and pH under major European forest types

Functional significance of tree species richness to ecosystem services provided by forests is not well explored. The influence of tree species richness on soil C, N and pH is the least studied. The few studies that attempted to look at impacts of tree species richness did not test the effect over spatial and bioclimatic gradients and some also used a complete dilution design which confounded and obscured the true richness effects. As part of the FunDivEurope project which investigated species richness effects across different spatial scales and bioclimatic regions, we examined the influence of tree species richness and the net diversity effect on soil pH, C/N ratio, soil C and N stocks in the forest floor and mineral soil. We hypothesized that tree species rich forests would sequester more C in soils and particularly in deep soil layers as a result of niche differentiation. We also anticipated that species-rich forests would have higher forest floor pH and lower C/N ratio compared with single species forests. We tested these hypotheses using an exploratory platform with a species richness gradient of 1-5 in mature forest stands in six regions across Europe, i.e. Finland, Poland, Germany, Romania, Italy and Spain. We sampled forest floors on an area basis and mineral soils were sampled by coring to a depth of 40cm when possible.

At the European level (across all six regions), tree species diversity expressed as species richness levels as well as by effective number of species based on the true Shannon index did not consistently influence soil C, N and pH.  However, there were trends in diversity effects on soil properties within certain regions. In Poland (at 20-30 and 30-40cm soil depths) C/N ratio significantly increased with species richness and in Spain soil pH decreased with species richness in the forest floor and 0-10cm depths without significant difference. Net diversity indices did not consistently show positive, negative or no relationship with increasing richness levels (2-5) at continental level, but mixtures had higher and positive net diversity effect in C/N, pH and C stock than the corresponding monocultures in some regions, richness levels and soil depths. In the forest floor, soil pH decreased and C stock increased with increasing conifer dominance at the continental level and within individual regions whereas difference in mineral soil C stock is linked to clay texture presence rather than species richness and identity. These results suggest that tree species richness per se is less influential to shape patterns of the studied soil properties as compared to species and/or functional group identities of tree species. Thus, it would be necessary to examine the effects linked to species, mixture and/or functional groups identities to address the interaction between species diversity and species identity.

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last modified 2014-06-19