Generic simulation model of forest growth, carbon and nitrogen dynamics, and application to tropical acacia and european spruce

In order to provide accurate assessments of forest stand development even in the absence of long-term growth and yield observations (as may be the case in developing countries and for less well-known species), a generic dynamic (cybernetic) simulation model has been developed representing tree growth, and carbon and nitrogen dynamics in a single-species, even-aged forest stand. The tree/soil system is described by a set of nonlinear ordinary differential equations for the state variables: wood, leaf, fine root, fruit biomass; assimilate; carbon and nitrogen in litter; carbon and nitrogen in soil organic matter; and plant-available nitrogen. All parameters are measurable ecophysiological quantities (no statistical parameter estimation). The model includes explicit formulations of all relevant ecophysiological processes such as: temporal and spatial light distribution and photosynthesis in the canopy; respiration of all parts; assimilate allocation; increment formation; nitrogen fixation, mineralization, humification and leaching; forest management (thinning, felling, litter removal, fertilization, etc.); and environmental effects (air pollution and insect damage). Application of the model requires specification of 38 tree-specific and 15 region-specific parameters (obtainable - except for root data - from simple field estimates or laboratory measurements not requiring time-series studies), 10 initial conditions for the state variables and 13 scenario parameters (e.g. nitrogen input, maximum nitrogen-fixing rate, litter removal, thinning and cutting schedule, pollution damage to photosynthesis, leaves, or fine roots, time and severity of insect calamity). The simulation model has been applied successfully to study stand growth behavior under different conditions of soil quality, forest management, and pollution and insect damage for broadleaf trees in a tropical climate ( Acacia auriculaeformis) Cunn. ex Benth. in South China) and coniferous trees in a temperate climate ( Picea abies (L.) Karst. in Central Europe). Despite the difference of species and climate, the model provides accurate representations of stand development under various conditions in both cases, yielding good agreement with standard yield tables (for spruce).