Juvenile Growth: Physiological Perspective

Understanding the physiology of juvenile oak growth and development is crucial to developing sound management practices for successful oak regeneration. Although the inherent growth potential of northern red oak is excellent, fast growth is seldom obtained in the field. Under the stresses typical of field conditions, multiple flushing usually occurs only if root systems are large and the seedlings are growing in full or nearly full light. Consequently, rapid shoot growth seldom occurs unless the overstory is destroyed or substantially reduced in density (Johnson 1979, Johnston 1941). Such events can result from fire, windthrow, insect- and disease-related mortality and defoliation, drought, mechanical and chemical release and timber harvesting (Johnson, 1993a).

Stem and leaf growth of northern red oak occurs in episodic flushes with cycles of shoot growth and apparent rest. Shoot growth progresses from a bud stage, to a linear stem growth stage, to a linear leaf growth stage, to a lag stage (apparent rest); then the cycle is repeated (Hanson et al 1986). Leaf development in northern red oak is acropetal and physiological leaf maturation continues past full leaf expansion, unlike that in most temperate tree species with simple leaves (Tomlinson et al 1989, 1991). Root growth in northern red oak seedlings has been found to be both constant (Halle and Martin 1968) and episodic (Vogel 1975), providing a mechanism to control shoot/root ratios. This shoot-root interaction enables the plant to respond to good environmental conditions with rapid flush cycles and height growth while maintaining a balanced shoot/root ratio.

Carbon allocation within plants is a major determinant of growth. The studies available on carbon budgets in northern red oak have established that carbon fixation, carbon distribution(or, carbon allocation within plant) and carbon partitioning (carbon flow among different chemical fractions) are all episodic and closely related to leaf and plant developmental stage (QMI) rather than chronological time.  Leaves of previous flushes are important contributors to the growth of subsequent flushes. Therefore, juvenile northern red oak seedlings growing in the field are dependent upon an adequate light environment to maintain a positive carbon balance and improve survival and early growth{Dickson 2000}.

In general, there is a lack of fundamental knowledge of the physiological processes controlling early growth and development in oaks compared to many tree species. This lack of knowledge is partly attributable to the relatively few studies on carbon fixation and allocation in oak.  However northern red oak has been the focus of a number of studies related to such physiological processes.  (Kramer and Decker 1944, Farmer 1975, Chabot and Lewis 1976, Hinckley et al 1978, Heichel and Turner 1983, Jurik 1986, Dickson et al 1990, Tomlinson and Dickson 1992). Knowledge of how carbon fixation and allocation change in response to changing environmental conditions could help us better understand a plants performance in natural environments and the potential impact of environmental stress on growth. Moreover, understanding carbon budgets of important oak species in more detail could also lead to improved management practices for natural regeneration or nursery production. In northern red oak carbon fixation and allocation are tightly linked with acquisition of other resources, such as nitrogen and water (Dickson and Isebrands 1991).  Moreover carbon fixation, carbon transport from source leaves, and carbon allocation within the plant are closely tied to the episodic or flushing growth habit of northern red oak {Dickson 2000}.

This information about northern red oak, while extremely valuable, should only be extrapolated to other oak species upon careful consideration of the similarities and dissimilarities to northern red oak.

See: Juvenile growth from an ecological perspective.