Boden, Waldernährung, Immissionen: die Untersuchungen der Forstlichen Bundesversuchsanstalt im Gleinalmgebiet

1998

S. 92-105, 355-356

Unselbständiges Werk

200065887

Forest decline symptoms in the Gleinalm area have been described since the end of the seventies and showed a peak at the beginning of the eighties. The Austrian Federal Forest Research Institute in Vienna (FBVA) conducted a number of investigations to explain the forest dieback in the area and to develop restoration measures. The results served as a basis for the current case study. Thus a brief overview of soil, plant nutrition, atmospheric load, and results of ferilization experiments, as described in several FBVA-reports, is given in this chapter. Soil types from lithosols to mesic and dystric cambisols. Podzols are rarely found. Soils texture is usually loamy sand, with low water storage capacity. Topsoils have generally low pH-values and low base saturation. Soils on gneissic bedrock have low Mg and Ca contents, soils on amphibolitic bedrock are low in K. Micronutrient contents in soil are rather low. Clearcutting, slashburning, subsequent production of cereals for several years and forest grazing in recultivated stands in the past were stress factors leading to nutrient depletion of the soils. Establishment of shallow rooting spruce monocultures on sites, where natural stand composition would be a mixture of Silver fir, Norway spruce and on eitrophic sites in lower elevations even European beech, had a negative influence on water and nutrient uptake. In inactive humus layers (wide C/N-ratios) under dense coniferous stands, nutrients are immobilized. Furthermore, water infiltration rates are reduced when a dense litter layer of spruce needles develops. Accumulation of lead on the forest floor and in the topsoil is an indicator of deposition load. Slightly elevated S contents of spruce needles - also an indicator of air pollution - can only be found in higher elevations. While currently deposition of air pollutants is low, higher load in the past from neighbouring industrial regions is likely. These impacts could have contributed to soil acidification. Spruce fine roots have rather low Ca/Al ratios. Exchangeable Al, Fe and H+ content of mineral soil correlates negatively with base cation content of the fine roots, indicating inhibited uptake of nutrients on acidified soils. Needle analyses show pronounced nitrogen and potassium deficiencies, low Ca values and, in some years, also low P and Mg contents. There are indications that drought periods in the 1980#s additionally had a negative influence on tree nutrition. Furthermore, disturbance of mycorrhiza as well as root and stem rot are responsible for reduced uptake and transprot rates of nutrients. Fertilization experiments show, that NPK fertilizers, applied on soil surface improve tree nutrition and growth. Thus fertilization can be recommended as a tool for forest restoration measures.