mechanistic ecosystem models

Mechanistic models describe biological, geophysical and chemical processes of a given ecosystem. They are designed to calculate the flux of energy, water, carbon and nutrients. Underlying processes such as photosynthesis, respiration and decomposition are incorporated as far as they are investigated. Therefore, the models are also called process or biogeochemical (BGC) models. BGC models act as a mechanistic description of the interactions between plants and the surrounding environment and are based on the current understanding of key mechanisms (Waring and Running, 2007).

BGC models use daily or monthly climate data together with general site conditions (e.g. water holding capacity, nitrogen deposition) thereby coupling vegetation with soil dynamics. They operate on stand levels and simulate carbon, water and nitrogen cycles for generalized biome types (Thornton, 1998) or species (Pietsch et al., 2005). A photosynthesis routine (Farquhar et al., 1980) is used to calculate carbon assimilation by the canopy. Leaf area index (LAI), being the main driver for photosynthesis, controls canopy radiation absorption, water interception and litter production. Net primary production (NPP) is calculated as the amount of assimilated carbon minus the autotrophic respiration.

Development and application

The Biome-BGC model (Thornton, 1998) in the version 4.1.1 (Thornton et al., 2002) was extended by work at BOKU with emphasis mainly on:

It was used in studies regarding:

  • growth response to environmental impacts (Hasenauer et al., 1999)
  • influence of thinning on ecosystem fluxes (Petritsch et al., 2004)
  • effect of different harvesting regimes (Merganicová et al., 2005)
  • analysis of coppice forests with standards (Pietsch & Hasenauer, 2007)