Leaf Development and Morphology

Growth of northern red oak occurs in episodic flushes with cycles of shoot growth and apparent rest (Borchert 1975, Reich et al 1980, Isebrands et al 1988, Dickson 1994). 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). Within-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). In controlled environments, several episodic flushes may occur, depending upon environmental conditions and culture. In nurseries, northern red oak seedlings usually exhibit two or three flushes in a season in the northern part of the species range and four to five in the southern part (P. Kormanik, personal communication). In the field, seedlings have one to two flushes in the north and two to three in the south, depending upon environmental conditions. The number of leaves within a flush varies with age and size of seedling. The first flush has 3 to 7 leaves, the second 5 to 10, and the third 8 to 15 (Hanson et al 1986). Freely growing coppice shoots can have many leaves and may even approach an indeterminate shoot growth pattern because of the large phototsynate reserves contained in the parent root system (Cobb et al 1985). Additionally, the number of leaves in a flush and the timing of flushing are under genetic control (Farmer 1975) (Isebrands et al., 1994).

Quercus morphological index

Knowledge of the seedling developmental stages and leaf maturation patterns is essential for studies of the carbon budget for northern red oak. Without careful attention to the exact stage of development, investigators can easily confound and misinterpret carbon fixation and allocation patterns (Dickson 1989, 1991). A Quercus morphological index (QMI) was developed to avoid these problems (Hanson et al 1986, Dickson 1994). The QMI is based on simple leaf and stem growth measurements of northern red oak seedlings. Four distinct stages have been defined for each flushing episode-bud swell (Bd), linear stem elongation (SL), linear leaf elongation (LL), and lag (Lg).

Quercus Morphological Index

1. To ensure uniformity of morphological stages of development in parallel studies of the same seed source at different locations,
2. To compare seed sources from year to year,
3. To determine shifts in plant development due to different treatments or environments, and
4. To relate the morphological stages of seedling development to specific biochemical, physiological, and anatomical events and processes.