SIMULATION OF FOREST STRESS FOR THE SOLLING SPRUCE SITE WITH SOILVEG

The SOILVEG model was applied to Selling to evaluate the effects of va rious stress factors on the Norway spruce stand (F1). First, hydrology , soil solution chemistry, tree growth and nutrient status for a Norwa y spruce were simulated for 1976-1989. SOILVEG could reproduce mean co ncentration levels for all major solutes. However year-to-year variati ons at greater depths, particularly for nitrate, often could not be ex plained. SOILVEG could also reproduce stem growth and nutrient concent rations in foliage. The model shows that in spite of large precipitati on surpluses and waterholding capacities, drought is a relevant stress factor for Selling. Magnesium is the most limiting nutrient for growt h of the F1 stand. In dry years, drought is the most important factor impeding uptake of Mg, in wet years pH is more important. However, it can not be concluded that a pll decrease due to acid deposition is an important stress factor for the F1 stand as the extent of the pH decre ase is unknown. Simulations with optimal irrigation and fertilization, combined with elimination of air pollutants doubled the current stem growth of F1. The absolute effect of individual stress factors can not be quantified because combined manipulations give a larger growth inc rease than may be expected from single manipulation. The importance of the stress factors for F1 can be ranked: fertilization > irrigation > air pollution. Simulations further indicate that elimination of S and N in throughfall initially (20 years) will decrease stem growth.