Acid deposition and forest nutrient imbalances: A modeling approach

Leaching of nutrients in areas with high acid deposition could be one of the causes to the nutritional imbalance observed in the tree leaf biomass in these areas. A simulation model is developed in order to study the interaction between soil and vegetation in acidified forests. A tree growth model, based on the nutrient productivity concept, is supplemented with soil processes to form an integrated plant-soil model containing the most important soil processes for acidification. The model is able to link decreased Mg availability in the soil and reduced growth caused by Mg deficiency. Simulation results show that the time and pH at which the stand will start to experience Mg deficiency is dependent on quantity and type of acid deposition, growth rate of the stand, initial base saturation and initial fraction of Mg on the cation exchange complex. The total amount of Mg initially present is not decisive for the time at which Mg deficiency will appear. The conceptual idea of nutrient imbalances in forest stands caused by acid deposition induced leaching is supported by this model.