Trees are very long-lived organisms with high potential birth rates. Thus, estimating the basic birth and death parameters of tree populations is intrinsically difficult over the time duration of most ecological studies. The sizes of trees from seedling to mature tree vary over five orders of magnitude. Trees grow large enough to alter aspects of their environment as they mature. This individual-environment feedback is not usually included in traditional ecological population models. Tree interactions obtaining essential resources of light, water, and nutrients involve tree geometry in vertically for light, spatially for nutrients and water, and volumetrically for interactions among tree crowns such as crown pruning (where the branches of a tree abrade the buds from limbs of neighbor trees and change the shapes of competing trees). These geometrical aspects of tree populations are omitted in the mathematical structures of most ecological population models which, at least until recently, considered only the time dimension. Tree populations represent a modeling departure from traditional population models. Significantly, forestry models from their origins have always attempted to predict a combined response of the sizes of trees and the number of trees on a given area.
Tree population models have deep historical roots that are often not appreciated by modern population ecologists, perhaps in part because the origins of many of these forestry-based approaches are in applied fields and are focused on practical, regional results rather than the development of a general theory. For this reason, it is useful to discuss forestry models from their beginnings through the evolution to the modern approaches.
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