MODELING PROCESSES IN FOREST SOILS - PROBLEMS, SIMPLIFICATIONS AND CAVEATS

The mechanistic simulations of chemical processes in forest soils requ ire estimates of uptake and release rates of nutrients from trees, as well as rates of microbial transformations of organic matter, chemical weathering and solute transport within the soil profile. Among the pr ocesses that affect the chemistry of forest soils chemical inorganic e quilibrium processes are best understood. An appropriate presentation of microbiological processes is lacking. Further uncertainty is introd uced by simplistic approaches to estimate nutrient uptake by trees and rates of chemical rock weathering. Parameters for processes are deriv ed from studies conducted at different spatial or temporal scales and therefore, may not always be consistent. Since kinetics cannot often b e adequately modeled, many processes are described assuming steady-sta te conditions, Moreover most European temperate forests are in a succe ssional transition phase and considerably off chemical steady-state. R easons are disturbances due to natural disasters (e.g., wild-fires) an d anthropogenic impacts (e.g., litter raking, acidic emmissions and ma nagement practices). Changing intensities of anthropogenic land-use an d silvicultural methods affect the chemical status of soils for decade s. A major constraint to modeling is the inability to properly account for long-term patterns that arise from the longevity of forests. Resu lts of simulation models are rather suitable to establish the boundari es of the status of soil chemistry under defined environmental conditi ons. Models often fail to accurately describe soil chemistry at partic ular locations and rimes. (C) 1998 Elsevier Science B.V. All rights re served.