Age-Related Changes in Tree Growth and Physiology

Abstract

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.