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Stosunki wodne w obumierającym lesie świerkowym w Karkonoszach

Kowalik P., Cudlin P.

Czasopismo Techniczne. Środowisko

2002

R. 99, z. 4-Ś

27--35

The programme of the research includes use of the SPAC model, taking into account how soil acidity will influence root density and transpiration of trees. Main results are connected to the simulation of these relation between root density and transpiration of trees, taking into account the actual soil water content and soil water stress (pF of soil water). These relations will indicate how the Mountain forest ecosystem can be influenced and which action would bring the most desirable results in terms of reforestation. In the North-Eastern part of Bohemia (CZ) stress and physiological disorders of higher plants are related to a strong forest decline. Total deforestation in some localities is connected with additional problems of reforestation. Research is directed into the pedo-environmental restriction to forest renovation in terms of soil chemical and physical constraints and the climate effect on the forest health. The knowledge on soil - tree - atmosphere - system using a SPAC model and the soil degradation, rooting density and soil water relations were evalued. The upper elevation coniferous forest trees live on the edge of disaster under continuous stresses. Soils are shallow to bedrock, nutritionally poor, too wet, with severe winters. Anthropogenic factors known from field studies to cause stresses in forest trees are mainly acidity (H2SO4/HNO3) and metal ions. Acidity (low pH) influences root systems and causing death of fine roots, which reduces water and mineral uptake. Sulphur and nitrogen compounds are the major pollutants having deleterious effect on forests. The sulphur deposition is perhaps the highest in the world here, up to 100kg S per ha and year. Decreasing root density is resulting with decreasing of tree transpiration and tree photosynthesis, often with death of the tree. Climatic data of the field were used to simulate diurnal course of the temperature, relative humidity and solar radiation during cloudy and sunny days. Results of simulation are giving the numerical values of root water uptake as a function of changing root density, influenced by soil degradation. The main assumptions were that the forest decline is a result of the water stress of trees. Forest under stress was damaged by insects, like Zeraiphera griseana, attacking several thousands of ha of the stand. Soil acidity under the influence of the acid rain drops even to the level of pH 2.4, standinglater on the level pH 3.4. The wet sulphate sulphur deposition was above 20 kg ha-1 year-1 in 1990 at Mountain Śnieżka, up to 100 kg S ha-1 year-1 in some locations, highest in the world. The annual concentrations of the sulphur dioxide SO2 in the area oscillate around 40-50 μg m-3 of air, while the annual SO2 concentration of 20μg m-3 may have a toxic effect on coniferous forest, especially under unfavourable climatic and edaphic conditions. Acidity influences root systems and soils, causing death of fine roots, reducing water and mineral uptake, altering microflora and litter decomposition, reducing mycorrhizae, resistance and vigor. The molar Ca/Al ratio below 1.0 shown to repress root growth. The working question in this paper was how decreasing root density L[v] cm cm-3 may influence spruce stands, but mainly leaf water negative pressure (water stress), leaf to air temperature (heat stress) and pulse of diurnal transpiration. The result of the simulation using SPAC model was the transpiration rate to leaf water negative pressure loop, given in fig. 2. Data on the root density was collected in the field. Diurnal meteorological data were taken from Pec near Śnieżka, 800 m a.s.l. Day 13th August 2000 (225th day of the year) was selected, sunny. Soil water potential was taken low as pF 2,9. Root penetration depth was shallow, about 50 cm. Root densities in the simulation were 5.0, 1.0, 0.1 and 0.05 cm cm-3, but in the field on the location of the strong forest decline the densities were below 0.4-0.5 and in the location of moderate forest decline the densities were about 1.0 cm cm-3. Critical behaviour of the trees was when root density was lower than 1.0 cm cm-3. Results of simulation may be confronted with the results of field measurements. Conclusions are: forest decline has a similar effect as the clear-cutting of the total stand; acid rain and clear-cutting are creating the conditions like in the acid bogs, with very low pH and low redoxEh; the research is indicating the importance of root regeneration ability, related to micro-topography, spatial variability of soils and phyto-sociology; new seedlings must be not distributed uniformly, but located only on the small "islands" elevated above the bog; biomanipulation and inoculation with microbes and fungi are not helping for seedlings survival; great need is indicated for new soil survey on micro-topography and spatial variability for new locations of the clusters of the seedlings.