Introduction
The pattern of individual tree growth is periodic over days and weeks depending on favorable temperature and moisture conditions. Over years and decades the growth pattern of trees is typically sigmoid whether it be measured by height, diameter, or volume over time. Tree growth pattern over years follows a typical sigmoid shaped curve. The pattern of tree growth in a stand varies between individuals, because trees growing together compete for light, water, and nutrients. Trees regenerating from seed start off at about the same size, but some trees grow more rapidly and others more slowly. Over time the vigorous or fast growing trees suppress the slow growing trees that may become stagnant or die. Through these interactions between trees – or competition – the forest stand changes through time; it is dynamic.
Between tree competition develops as they begin to compete for aboveground resources (light) and below ground resources (moisture and nutrients). In moist environments the onset of competition usually occurs around the time of canopy closure; in drier environments, characterized by more wide-spaced trees, competition is belowground between roots for scarce moisture resources. In the woodland the trees do not close the canopy, and the competition is mainly between roots for soil moisture. In a forest the trees usually achieve canopy closure, at which time competition for light and tree height become important.
Trees in a stand are differentiated into crown classes, because the growth of some trees slows more than others so that as the stand ages, a range of tree sizes develops that can be classified in to different crown classes – according to the trees relative position in the canopy.
Disturbance is a determinant of forest structure and competition between trees, because forests are continually impacted by external forces to modify the structure of the stand – often through killing and felling of trees. Sources of disturbance include wind, fire, drought, water, ice, and biota. There is a whole area of ecology devoted to describing and defining disturbance, and our intention here is to briefly identify the interaction between trees and disturbance in creating and modifying stand structure.
Terminology and concepts: definition of a stand, even-aged, mixed-age, competition, canopy, stand structure, gap formation, shifting-mosaic steady state, old growth, and landscape scale.
Video Lecture
Please view the following video lecture and video for this topic.
1.1 Lecture: Forest Regeneration and Tree Growth
Reflection Questions
Please answer the following self-reflection questions. After formulating your answers, you may post them online at the Knowledge Café for this course as a way to share your ideas and glean knowledge from other students’ responses.
- Compare and contrast the characteristics of even-aged and mixed-aged stands. Do even-aged stands eventually become mixed-aged?
- As a growth and dominance strategy, what are the disadvantages of accumulating starch reserves for epicormic growth?
- Should disturbances be seen as an integral component of the forest type and not an external destructive force?
Supplementary Readings
Textbooks
Bormann, F.H., & Likens, G.E. (1981). Patterns and Process in a Forested Ecosystem. New York: Springer-Verlag.
Oliver, C.D., & Larsen, B.C. (1996). Forest Stand Dynamics (Updated ed.). New York: McGraw-Hill.
Peterken, G.F. (2001). Structural dynamics of forest stands and natural processes. In J. Evans (Eds.), The Forests Handbook (pp 83–104). Blackwell Science Ltd. ISBN 0-632-04821-2.
Articles in Journals
White, P.S. (1979). Pattern, process and natural disturbance in vegetation. Botanical Review 45, 229-99