Forest dynamics in the Pfyn forest in recent centuries (Valais,Switzerland,Central Alps): interaction of pine (Pinus sylvestris) and oak (Quercus sp.) under changing land use and fire frequency

Pinus sylvestris is co-dominant in many areas of eastern and northern Europe. In Switzerland, the Pfyn forest is considered to be the largest natural forest of Pinus sylvestris. Its development under changing land use during recent centuries is largely unknown. Of particular interest is the interaction between pine and oak, for it has been suggested that oak has benefited from the strong decline in economic uses of the forest such as pasturing, litter removal and logging. In order to improve understanding of the dynamics in this particular forest type over time, the vegetation and fire history of the Pfyn forest were reconstructed by pollen and charcoal analyses of the sediments of Pfafforetsee. Four phases of decline in Pinus pollen percentages are explained by logging events and other anthropogenic activities during recent centuries. During the twentieth century human impact on Pinus was probably exacerbated by forest fires. When human influence ceased or declined, Pinus was able to regain its former importance within a few decades. Whereas Pinus experienced considerable change, Quercus species (Q. pubescens, Q. petraea and Q. robur) exhibit constant and low pollen values throughout the record. Under constant climatic conditions, pine should therefore not suffer late-successional replacements by oak in the Pfyn forest. This finding is especially important for nature conservation and forest management, since strong decline in Pinus sylvestris in the canton of Valais has also been interpreted as a consequence of successional dynamics towards a more natural vegetation.