Aboveground nutrient cycling and forest development on poor sandy soil

The aboveground nutrient turnover of three ecosystems representing the main stages of heathland forest succession in NW Germany was investigated in a comparative study with regard to nutrient availability of the soil and light availability below the canopy. It was expected that nutrient availability would play a decisive role in forest development on nutrient poor acidic soil. The results show that the input of nutrients into the Calluna heathland is higher than the annual aboveground turnover of N, P, Ca, Mg, and K via litterfall. Compared to the pioneering birch-pine forest, the annual aboveground turnover of nutrients within the Calluna heathland, and therefore the nutrient availability is very low, while the light availability below the canopy is high. The increasing productivity of the growing successional forest is combined with an increasing nutrient turnover, mainly via litter fall. As a result, the increasing nutrient availability favours shade tolerant species with a higher nutrient demand at the late stages of succession. Consequently, the presumed terminal stage of succession, the oak-beech forest, is characterized by low light availability below the canopy and higher nutrient supply according to the resource-ratio hypothesis of Tilman (1985, 1986, 1988).