Application of the model fiwald to the Solling spruce site

Abstract

The physiological model of Norway spruce even-aged stands, fiwald, was applied to the Solling F1 spruce site, based on the data and the scenarios supplied by the Workshop on Comparison of Forest-Soil-Atmosphere Models, Leusden. Several simulation experiments were conducted, including simulation of the development of the F1 stand for the last two decades and analysis of effects of atmospheric deposition, water and nutrient stress. The results emphasize the impact of deposition-driven base cation depletion in mineral soil on tree nutrition. Additionally, a N shortage can be detected. However, the simulations show that stand productivity and growth are mainly limited by base cation deficiency. In the case of N fertilizing the productivity is increased in the first years, but decreases significantly afterwards due to pronounced Mg deficiency and needle loss. The reason for the more prominent Mg deficiency under N fertilizing is the accelerated consumption of the soil Mg resources by the biomass growth. Water stress has, even in drought years, only limited impact on gas exchange and stand growth. In the ‘business as usual’ scenario the stand is able to survive, but the needles show Mg deficiency, the productivity is decreased and the trees are susceptible to changes in the deposition regime. In the ‘improved environment’ scenario the amount of available base cation nutrients increases slowly by supply from silicate weathering and deposition, the nutrient deficiency disappears, and the productivity finally reaches the level of the seventies, though the stand is much older.