Trees are sessile organisms and this ties them unavoidably to the given spatial arrangement. As trees grow in size their demands on resources and growing space increase. When resources are no longer adequate for all individuals some of them will die and the number of plants per unit area will decrease. The three principal interacting processes involved in the growth of a tree are: resource capture as a response to the immediate environment and leading to tree growth, allocation of growth to the development of the 3-D structure of the tree, and modification of the immediate environment, described as a 3-D distribution of the resource flux. Forest dynamics result from the interplay of these processes, and are primarily reflected in crown development: if the tree can lift its crown to a position that affords sufficient light in comparison to its neighbours, then it will survive in the forest, otherwise it will become suppressed and is liable to die. As trees are modular organisms, they develop by the repetition of physically interrelated elementary units e.g. internodes and leaves. By varying the intensity of proliferation and senescence of the elementary units it possible for them to respond plasticly with their shape and overall form to their immediate environment.
This contribution reviews how the spatial-temporal dynamics of forests as a result of the interaction of structural and functional properties of trees has been realized in models. A special emphasis is given to the so-called functional-structural models. They view the tree as consisting of a number of elementary units that makes possible to account for its true 3-D structure and to combine with it resource use and growth at a detailed level.