Understanding the relation between changing climate and forest tree diversity on production of tree biomass in forests is fundamental for developing strategies for carbon sequestration, particularly, because Central-European forestry is conducting a conversion of monospecific into mixed stands. A warmer and drier climate as predicted for huge parts of Central Europe may substantially influence the tree species productivity and tree composition over the next decades. We quantified above-ground production of temperate deciduous tree species in monospecific stands (Fagus sylvatica), 3-species stands (F. sylvatica, Fraxinus excelsior, Tilia spp.) and 5-species stands (F. sylvatica, F. excelsior, Tilia spp., Carpinus betulus, Acer spp.) over three years to examine if (i) mixed stands are more productive than monospecific stands, (ii) how tree species differ in the productivity of stem wood, leaves and fruits under different climatic conditions.
Results/Conclusions
We found distinct differences between the tree species regarding total and seasonal production of biomass. Seasonal growth dynamics of Tilia were more dependent on the prevailing climatic conditions with slow stem wood increment in cool and moist spring, and much faster in years with warm spring. Fraxinus exhibited the highest wood production of all species, and reached 60 - 80% of its annual increment in basal area already at the end of June. Fagus had increasing mast years after the summer drought in 2003, with fruits mass exceeding foliage mass. Leaf biomass remained remarkably constant over the three years. The observed differential seasonal growth patterns among the species did not result in increased productivity at the plot level compared to the monospecific stands. Tilia, Acer and Carpinus invest more carbon into the production of foliage and, thus, enhance carbon cycling in mixed species stands, whereas the production of stem wood in Fagus trees exceeds leaf production and results in longer carbon storage in plants in monospecific stands. Our data suggest that above-ground net primary production is more under the control of tree specific traits than dependent on tree species diversity. Therefore, forest productivity will strongly rely on the tree species adoptions to changing climate.