The spread of ash (Fraxinus excelsior) in some European oak forests: an effect of nitrogen deposition or successional change?

The influence of nutrient availability on the spread of the European ash (Fraxinus excelsior) in predominantly oak forests (Quercus petraea, Quercus robur) have been evaluated in forests of Cesky kras, Ceske stredohori (both in the Czech Republic), southern Sweden and southwestern Slovenia. Ash has dispersed in ecosystems with lower availability of P as well as in ecosystem with lower availability of N. Decomposition of organic material formed in the forest ecosystem (and formerly removed by human forest management—coppicing, grazing, litter raking, etc.) constitutes a much more important source of enrichment of the ecosystem in N compared with anthropogenic deposition. Furthermore, the greater availability of N and P in soils that are well supplied with exchangeable cations does not provide an adequate explanation for the spread of ashes. On the other hand, stage of succession is an important factor. Therefore, the spread of ash in ageing oak-dominated forests appears to be a natural process.