PICUS v1.4, is a hybrid patch model combining elements of a 3D patch model and a process-based forest production model. The structural resolution is 10 x 10 m, spatial interactions among patches are modelled with a three-dimensional canopy light regime and spatial seed dispersal. The concepts of inter- and intra-species competition for resources follow a modified patch model concept (Lexer and Hönninger 2001), whereas net primary productivity is derived from utilizable solar radiation and canopy quantum use efficiency following the 3-PG approach (Landsberg and Waring, 1997). The coupling of both elements is inter alia accomplished via the leaf area of a stand and is described in detail in Seidl et al. (2005a). Below-ground processes are modelled applying a biogeochemical process-model of Carbon and Nitrogen cycling (Currie et al., 1999, see also http://www.al.umces.edu/currie/trace.htm). The PICUS modelling framework incorporates a flexible management module allowing for all sorts of thinning and harvesting operations as well as for planting. Furthermore, in cooperation with the Institute of Forest Protection, BOKU a module for simulating biotic disturbances by the bark beetle Ips typographus, and a rockfall module in cooperation with GeoExperts Ltd. are incorporated. The general model structure is given in figure below.