Age‐Related Changes in Tree Growth and Physiology


Trees pass through specific developmental phases as they age, including juvenile to adult, and vegetative to reproductive phases. The timing of these transitions is regulated genetically but is also highly influenced by the environment. Tree species have evolved different strategies and life histories that affect how they age – for example some pioneer species are fast growing and become sexually mature at younger ages but have shorter life spans. Trees do not have a strictly programmed senescence, and their life span is influenced by factors including challenges associated with increasing size, and ability to cope with environmental stress such as water availability, rot fungi, insects and disease pressure. Some long‐lived tree species escape threats in exceptionally dry environments, while others use clonal reproduction through sprouts from stumps or roots to enable the same genotype to persist for thousands of years. On longer timescales, tree species migrate across landscapes to suitable environments.

Key Concepts

  • Forest tree species display a range of strategies and life histories that affect their life span and ageing and can be described in terms of forest succession concepts.
  • Trees undergo juvenile to adult transitions that can be reflected in distinct differences in morphology of leaves, changes in physiology or changes in the anatomy and biochemical makeup of wood.
  • Trees also undergo a period of vegetative growth before becoming sexually mature and competent to make reproductive structures (flowers in angiosperm trees or strobili in gymnosperm trees).
  • Trees do not have a genetically programmed life span or senescence. Life span is affected by limitations imposed by size and abiotic and biotic factors.
  • In some species, while the original tree stem may die, clonal sprouts can form, allowing the same genotype to live for thousands of years.
  • Over long timescales, tree species migrate to accommodate changes in climate over time.

Keywords: climate change; forests; forest mortality; tree physiology; tree development

Figure 1. Forest succession can lead to mortality. On this slope near Rabbit Ears Pass in Colorado, spruce (green trees) can be seen encroaching into an aspen stand (yellow trees). In the absence of disturbance such as fire, the longer lived shade‐tolerant spruce can establish under the aspen, eventually overtopping and replacing the stand. Photo credit: Barry Lilly, US Forest Service.
Figure 2. Extreme changes in maturation in longleaf pine. Longleaf pine frequently establishes in sites after fire and can grow for many years in a ‘grass’ stage, which helps protect the apical and cambial meristems from fire (a). After establishing a root system that can support rapid growth, seedlings switch to elongative growth to achieve the mature form (b). Photo credit: John Kush, Auburn University.
Figure 3. Life span of individual stems in aspen is affected by fungal rots. (a) A fruiting body of Phellinus tremulae, a shelf fungus and the cause of white trunk rot in aspen. (b) White trunk rot can cause death through direct damage to living sap wood and can weaken stems by decaying the heartwood, leading to susceptibility to mechanical breakage by wind or snow. An interesting ecological benefit – woodpeckers prefer making their nest cavities in aspen with decay. Photo credits: Jim Worrall, USDA Forest Service.
Figure 4. Survival strategies for long‐lived tree species. (a) Populus euphratica growing in Inner Mongolia, China. In contrast to most trees within the genus Populus, individual stems of P. euphratica can persist for several hundred years and live in an extremely dry environment. While presenting obvious challenges, the dry environment may be the key in reducing the danger of parasitic and rot‐causing fungi that can limit life span. (b) Pinus longaeva growing in the white mountains of California. (a,b) Photo credit: Suzanne Gerttula, US Forest Service. (c) Populus tremuloides clone near Lake Tahoe, California. Aspen (P. tremuloides) can propagate by ‘root suckering’, where new shoots arise from roots of established trees. The young trees in the foreground are clonal shoots extending into a meadow from the roots of older trees. In this way, aspen can incrementally pioneer new sites or else re‐establish quickly after disturbances including fire. Large aspen clones can occupy dozens of hectares and live for thousands of years. (c) Photo credit: Andrew Groover, US Forest Service.
Figure 5. Tree populations and species migrate over time in response to changes in climate. (a) The migration of single‐leaf piñon pine (Pinus monophylla) in the Pacific Southwest of the United States since the Last Glacial Maximum, moving from refugial regions in the current Mojave and Sonoran Desert. Data points correspond to the locations of and approximate dates of arrival (years before present) of expansion northward to its current distribution limit north of Reno, Nevada. Modified from Grayson © University of California Press. (b) Topography, water availability and other local factors influence migration patterns over the landscape. In this location in the Toquima Range of central Nevada, single‐leaf piñon (arrows indicate individual piñon trees) is moving downslope to take advantage of higher water availability, as well as upslope as warming temperatures open ecological windows at higher elevations. Photo credit: Connie Millar, US Forest Service.


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Groover, Andrew(Jun 2017) Age‐Related Changes in Tree Growth and Physiology. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0023924]