Greater abundance of Fagus sylvatica in coniferous flood protection forests due to climate change: impact of modified root densities on infiltration

Climate change is expected to modify the spatial distributions of zonal forest communities and thus, their species compositions. The aim of this paper was to study the impact of higher abundance of beech on water storage capacity in current coniferous flood protection forests due to varying root densities of the main tree species. Two forest communities in the northern pre-Alps in Switzerland with similar soil properties but varying in species composition were investigated (space-for-time substitution). It was assumed that the Vaccinio myrtillii-Abieti-Piceetum (site A) will be replaced by a Luzulo-Abieti-Fagetum (site B). We irrigated 16 hydromorphic soils (1m2, 70mm/h, three consecutive irrigations) at site A and 10 at site B and recorded water-content variations with time domain—and frequency domain reflectometry. Roots were extracted from soil cores taken from the positions where the water-content probes were inserted, and digitally measured. Infiltration capacity ω I was mainly limited to the upper soil at site A but was approximately constant down to 0.7m depth at site B. Between 0.3 and 1.0m soil depth, root densities at site B exceeded those at site A. Root density was the main predictor for ω I (R 2=0.57) at site A as shown by a multiple linear regression analysis. Assuming that the root density in the current coniferous forest (A) will increase to that of the beech stand (B) due to the greater abundance of beech, the water storage capacity will increase by 9.2mm in consequence of the expected forest transformatio