Jahrringanalytische Untersuchungen in immissionsgefährdeten Waldschadengebieten des Walliser Rhonetals

Abstract

Abstract. The pine forests of the Rhone Valley are severely damaged. Possible causative agents are fluoride and other harmful gases such as S02, HCl and NOx in the emissions of nearby aluminium smelters and chemical plants. Drought and aging may also have contributed to the damage. Core samples and trunk discs from damaged and undamaged Stands near Martigny were investigated using annual ring analysis. After Visual dating of the samples by means of «pointer» rings formed during dry years, growth disturbances were pinpointed. Radiodensitometrical measurements followed, and age trends were eliminated using mathematical growth functions. A model of the relationship between annual ring, temperature and precipitation was constructed for the emission-free period 1874–1940 and extrapolated to give the values expected for the last hundred years if growth were influenced by climatic factors only. Annual increments for the period 1941–1979 were 20–30% below the expected value, regardless of tree age, indicating a harmful factor not primarily related to drought or aging. Growth disturbances occurred most commonly during the droughts of the forties and may be regarded as resulting from the emissions which began in 1938 when a new aluminium smelter was built in the main valley: it stood in the mainstream of the prevailing winds and was without filters until 1965. The harmful emissions of the late thirties may have damaged the trees to such an extent that they could no longer withstand natural Stresses and finally died 30–40 years later. Although the fluoride emissions are not causally related to the forest damage, they provide a valid explanation of the results.