The functional structural plant models (FSPMs) can be defined as models that combine descriptions of metabolic (physiological) processes with a presentation of the 3D structure of a plant. They contain usually the following components 1) Presentation of the plant structure in terms of basic units, 2) Rules of morphological development and 3) Models of metabolic processes that drive the plant growth. The main emphasis in these applications has been individual plants. It is understandable because, due to the detailed description of the plant structure, and consequently, of the local environment of each organ, the FSPMs tend to require a large number of parameters and/or input data. Owing to the large amount of information they contain about the plant to be modeled, they also tend to be computationally heavy. In the following we shortly describe how the three FSPM model components have been realized in the LIGNUM model. Three basic units (Tree segment, Branching point and Bud) are used. We are using the STL template library of C++ to define a blueprint of a tree that can be instantiated by actual representations of the species specific components. We are using four generic algorithms for traversing the data structure of the tree and to make calculations. L-systems are used for specifying the morphological development ofthe trees. We present three examples of applications made using LIGNUM: a calculation of optimal leaf traits in Sugar maple saplings, a system for storing and analyzing information on decay in city trees and simulation ofgrowth ofa tree stand.