Age-Related Changes in Trees

One characteristic that distinguishes trees from other plant species is the presence of long-lived shoots. While woody shrubs and herbaceous perennials may appear to be long-lived, the longevity of a single shoot is relatively short; ranging from a few months to a few years. The long life spans attributed to shrubs and perennials reflect the replacement of 'older' shoots with new ones on a continuing basis. Trees, on the other hand, retain a single main growing shoot throughout their life cycle with the attainment of massive size as a result. Indeed, trees are among the largest and most long-lived organisms on earth (Table 1). The bristlecone pine, Pinus aristata, is generally recognized as the longest-lived organism on earth with recorded life spans of over 4,000 years. Numerous North American forest tree species have life spans of 500 years or more (Fowells 1965). Trees in landscape situations do not live nearly as long as those under native conditions. Horticulturists speak of "useful life span" or "landscape life span."