Effects of harvesting on nutrient leaching in a Norway spruce (Picea abies Karst.) ecosystem on a Lithic Leptosol in the Northern Limestone Alps

On a heavily karstified site in the Northern Limestone Alps (Austria), nutrient budgets and leaching in Norway spruce stands were investigated along a chronosequence (clearcut, 10-year-old plantation (25% cover of planted and naturally regenerated spruce and larch, 75% weed cover) and mature stand). The soils were Lithic Leptosols on very pure limestone. Nutrient fluxes were studied during three growth periods (4–5 months each). Despite of inorganic nitrogen inputs from precipitation between 5 and 10 kg ha^–1, inorganic nitrogen output with seepage water from the mature stand and the regeneration plot was only 0.5–1.2 kg ha^–1 during these periods. In the first and second growth periods after clearcut, inorganic N fluxes with seepage increased to 20 and 30 kg ha^–1, respectively, declining in the third growth period to 8 kg ha^–1. DON output during the growth period was between 3 and 6 kg ha^–1 in the mature stand and 7 and 11 kg ha^–1 in the clearcut as well as in the regeneration plot. K output rates achieved 30 kg ha^–1 in the first, 20 kg ha^–1 in the second and 9 kg ha^–1 in the third growth period after clear-cutting while output rates during the growth periods were less than 2 kg ha^–1 in the mature stand and in the regeneration plot. K pools in the humus layer were only 150–210 kg ha^–1, total K pools including above and below ground biomass in the mature stand were 360 kg ha^–1. Thus, post-harvest hydrological losses comprise a substantial depletion of K for this specific ecosystem. Since precipitation is high in this area (1400 mm a^–1), forest growth is limited by nutrient rather than by water supply. Needle analyses already indicate a deficient potassium supply. Harvesting and post-harvesting losses of K in combination with elevated nitrogen deposition may have negative influences on the stability of forest stands on the studied sites.     

Revitalization experiments in magnesium deficient Norway spruce stands in Austria

Amelioration of degraded forest ecosystems on acidic substrates showing the new type of forest decline is a major goal of forest management. A number of experiments show positive effects of Mg-application to systems suffering from Mg-deficiencies. The current paper compares experiments conducted in the Austrian part of the Bohemian Massif, where both effects on soil solution chemistry and effects on plant nutrition, vitality and growth were investigated. It turned out that any type of Mg-source is able to improve Mg-nutrition of trees; both a neutral salt like KIESERITE as well as alkaline reacting magnesite and dolomite derived materials. A positive reaction of vitality and growth could however only be induced with dolomitic lime or magnesite. Using mineral NPK fertilizers, even with high Mg-content, induced Mg-deficiencies and led to nutritional imbalances. In addition significant NO₃ ^--leaching occured. On the other hand an organic slow release fertilizer (BACTOSOL*) amended with magnesite derived fertilizers (BIOMAG**) led to balanced nutrition and a fast recovery of tree health status, as judged by crown transparency, vitality index and growth rates. In both cases, when either magnesite derived compounds or combinations with the organic slow release fertilizer were applied, NO₃ ^--leaching occured only during the first three years after fertilization. The leaching rates declined afterwards to values comparable to unfertilized plots, while Mg-content of the soil solution could be elevated compared to the CONTROL, showing the sustainability of proper fertilization.     

Modeling of nitrogen dynamics in an Austrian alpine forest ecosystem on calcareous soils: a scenario-based risk assessment under changing environmental conditions

We modeled the behavior of an Austrian alpine forest ecosystem on calcareous soils under changing climate and atmospheric nitrogen deposition scenarios. The change of nitrate leaching, emission rates of nitrogen compounds, and forest productivity were calculated using four process-oriented models for the periods 1998-2002 and 2048-2052. Each model reflects with high detail a segment of the ecosystem: PnET-N-DNDC (photosynthesis-evapotranspiration-nitrification-denitrification-decomposition; short-term nitrogen cycling), BROOK90 (water balance for small and homogenous forest watersheds), HYDRUS (water flux in complex and heterogenous soils), and PICUS v1.3 (forest productivity). The nitrogen balance model (NBM) combines the individual results into a comprehensive picture and extends the specific values beyond the limits of the individual models. The evaluation of the findings was outlined with TRACE, a model enabling a long-term prognosis of nitrogen cycling in annual time steps. Temperature increase and nitrogen input are influenced by various components and processes of the forest ecosystem. An increase of the temperature of 2.5 degrees C led to an enhancement of the N2O emission rates and affected the mineralization and the nitrification rates with the consequence of increased nitrate leaching into the subsoil. Enhanced nitrogen input also showed notable effects on nitrate leaching.