The shape of a tree is an ecological construct, since its form is dependent on the habitat and the stresses of the environment. Open-grown trees, such as those in gardens and parks, generally have foliage extending along the length of the trunk (bole) for a considerable distance. Forest trees, on the other hand, compete for growing space and generally have an expanse of foliage-free bole below a more limited tree crown. The aggregate of the tree crowns constitutes the canopy of the forest, and this may be displayed in a single layer or stratified into several layers, depending on the number and kinds of trees that make up the forest.

The ultimate goal of tree ecophysiology is to determine why a certain tree grows where it does. The complex answer includes the following elements: its seed or source; its fitness for survival, growth, and reproduction in that particular habitat; and its ability to compete favourably with other inhabitants of the habitat.

The growth, structure, and composition of a forest are a function of the intensity and quality of light streaming into it. Trees partition the light resource in time and space.

The time dimensions include seasonal, successional, and developmental time. In seasonal time, the time of leafing out and leaf fall and the time of flowering, seed formation, and germination are considered. In successional time, clearings in forests initiate growth in preexisting seedlings and new germinants, which causes progressive changes in the distribution of light and results in changes in species composition over time. In developmental time, changes take place in the physiology and morphology of the tree with age.

Trees can reach or approach adaptation to a specific habitat by different combinations of morphological, anatomical, and physiological traits. The more closely the trees use the same subset of adaptive features, the more strongly they compete with each other for habitat resources. For this reason, trees of the same species compete more strongly with each other on a site than they do with members of other species.