Growth periodicity is generally conceived as a set pattern of growth incited by internal factors and influenced by environmental conditions (Morrow, 1950). The inherent alternation between periods of abundant root and shoot growth and little or no growth is thought to serve as a mechanism for coping with environmental stresses (Reich et al., 1980). Periodic root and shoot growth may occur simultaneously in an apparent coordinated fashion (e.g., Cripps, 1970; Harmer, 1990) or in an alternating pattern (Ploetz et al., 1993; Thaler and Pages, 1996). Many woody plants [e.g., apple (Malus domestica Borkh.), jarrah (Eucalyptus marginata Donn ex Sm.)] exhibit a bimodal pattern of root growth with periods of active root elongation occurring in late spring and autumn interspersed by a period of rest or reduced growth, often in summer (e.g., Cripps, 1970; Dell and Wallace, 1983). Although many authors reported the occurrence of root growth before spring budbreak or initial spring shoot elongation [Cedrus atlantica (Endl.) Manetti, Pinus nigra Arnold ssp. laricio Poir. var. corsicana Loud.] (e.g., Kaushal et al., 1989; Wargo, 1983), others observed root growth beginning after spring budbreak or concomitant with shoot growth [Picea sitchensis (Bong.) Carr., Corylus colurna L.] (Ford and Deans, 1977; Harris et al., 1995).
In many instances, one dominant factor may appear to dictate root and shoot growth periodicity, but in most situations, a combination of factors is responsible. Root growth periodicity depends on genetic species-specific responses (Wargo, 1983) to multiple interacting and interdependent factors such as unfavorable environmental conditions like drought or high temperatures (Lyr and Hoffman, 1967), top pruning (Gilman, 1990), both excesses and shortages of soil moisture content (Bevington and Castle, 1985), transplanting (Harris et al., 2002; Wang and Zwiazek, 1999), stage of shoot development (Bevington and Castle, 1985; Cripps, 1970), and measurement method (Harris et al., 1995).
The functional balance hypothesis describes the growth relationship between roots and shoots as being continuously modified (Brouwer, 1983). As such, rhythmic root and shoot growth in trees results from feedback mechanisms associated with maintaining a favorable root:shoot ratio (Borchert, 1973) and may be a consequence of water stress incited by an unfavorable root:shoot ratio associated with rapid shoot growth (Harmer, 1990) or a decline in carbohydrate reserves during shoot elongation (e.g., Deans and Ford, 1986; Wargo, 1979).
Although many studies concluded fall planting to be superior to spring planting (Hinesley, 1986; Watson and Himelick, 1983; Witherspoon and Lumis, 1986), other studies concluded fall planting is inferior (Buckstrup and Bassuk, 2000; Larson, 1970; Watson et al., 1986) or has no advantage to spring planting (Harris et al., 2001; Watson and Himelick, 1982). For example, early fall-transplanted sugar maple and northern red oak (Quercus rubra L.) began root regeneration earlier and regenerated more roots in the first season after transplant than mid-fall- and spring-transplanted treatments (Harris et al., 2002), whereas fringe tree (Chionanthus virginicus L.) did not regenerate roots outside the transplanted root ball until early July regardless of season of transplant (Harris et al., 1996).
A more complete understanding of root system regeneration patterns and relationships between shoot and root growth of newly transplanted trees will enhance our fundamental knowledge of root ecology and transplant establishment, which can result in practices that hasten the establishment of transplanted landscape trees. The objectives of this study were to determine the periodicity (timing and magnitude) of first-season root, shoot, and trunk growth of sugar maples growing in field or container, the two most common production methods. Trees were either grown in the field and transplanted with root balls wrapped in burlap or container-grown in the pot-in-pot (PIP) system (Ruter, 1997) and transplanted at various times of the year.
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