Effect of stand age on fine-root biomass and biomass distribution in three European forest chronosequences

Fine-root (<2 mm) biomass and biomass distribution were determined in different age-classes of three European forest chronosequences dominated by Fagus sylvatica L., Picea abies (L.) Karst., and Quercus cerris L., respectively. Root samples were taken with the auger method. There was a clear effect of stand age on standing fine-root biomass, with the highest fine-root biomass in adult but not mature stands. The vertical fine-root biomass distribution showed, at all sites, high densities of roots in the top soil layers and with depth a gradual decrease of fine-root biomass density. The difference in total fine-root biomass between the different age-classes appeared to be due to differences in the top soil layers. Fine-root biomass in the lower soil layers was less variable along the life cycle of the forests. Only in very young stands, specific root length of fine roots was higher than in the other age-classes. The present data together with other published values suggest that fine-root biomass in tree stands develops in three phases: rapid increase after a clear-cut harvest up to a maximum of fine-root biomass; a decrease during maturation of the stand; and a steady-state in mature stands.