Leader, Needle, Cambial, and Root Growth of Certain Conifers and Their Interrelations

Abstract

1. The seasonal course of leader elongation, needle elongation, and cambial growth of certain conifers, particularly red pine and white pine, was measured during the 1931 growing season near Keene, New Hampshire. 2. Leader elongation in red pine began in late April, reached its maximum by June 10, and ceased about the middle of August, a growing period of approximately 105 days. Ninety-six per cent of this growth was made during the 60 day period from May 15 to July 15. Older trees were slightly later in their seasonal course of leader elongation than were younger trees. Trees located on southwest slopes started growth earlier than those located on level areas. 3. Leader elongation in white pine started slightly later than in red pine but reached its maximum at the same time (June 10) and ceased growth at the same time. Ninety-six per cent of the growth occurred from May 15 to July 15. 4. Leader elongation in pitch pine followed a seasonal course similar to that of white pine. Ninety-seven per cent of this growth occurred from May 15 to July 15. 5. Leader elongation in white spruce started the middle of May, reached a maximum June 10, and ceased July 23, a growing period of about 70 days. 6. Leader elongation in balsam fir started late in May, reached a maximum June 23 (two weeks later than the other species), and ceased July 23, a growing period of about 65 days. 7. From June 13 to June 29, 60 per cent of the leader elongation of red pine occurred at night, 40 per cent during the day. A correlation of +0.744 ± 0.075 existed between night growth and minimum temperature. No significant correlation existed between day growth and temperature. 8. The needles located at the base of the leader in red, white, or pitch pine pass through their grand period of growth earlier than do those located higher up on the leader. Those at the tip began elongation about June 5. 9. Needle elongation in red pine began about May 15, reached a maximum late in June, and ceased in early September, a growing period of 110 days. Ninety-four per cent of the growth occurred during the 60 days from June 10 to August 10. 10. Needle elongation in pitch pine was similar to that of red pine; white pine was slightly more tardy in its development than red pine. 11. Needles of the pines investigated grow from a meristematic region at their base. They do not elongate after the first growing season. 12. Daily needle elongation in red pine showed a correlation of +0.627 ±0.08 with the mean temperature. 13. Cambial growth in red pine as measured by the MacDougal dendrograph began in early May, reached a first maximum June 2, decreased slightly and reached a second maximum July 9. Growth ceased in early October, a growing period of 150 days. There was no correlation between the meteorological conditions and the double maximum in the growth rate. The first maximum is probably associated with the development of spring wood and the second maximum with the development of summer wood. 14. Stevens reports that the roots of white pine begin to elongate the middle of April, reach a first maximum June 8, decrease, rise to a second maximum on October 4, and cease in early November, a growing period of about 205 days. 15. There is a certain interrelation between the activity of the different growing regions of the tree. In early June there is a great surge of growth in leader, roots, and cambium at approximately the same time. This spurt of growth is made possible by the great amount of readily available reserve foods stored in the tree. There is probably a causal relation between these different growth activities having to do with the absorption, transportation, and utilization of water. 16. After this first surge of growth the needles reach their maximum growth rate, followed by the second maximum of cambial growth. After nearly all growth is completed and the full complement of needles is functioning, the roots reach their second maximum rate of elongation. 17. It is suggested that there is an internal balance between the metabolic activities of the different growing regions of the plant which determines the time of maximum development of needles, cambium (late wood formation), and roots. After the reserve foods are exhausted this balance is necessitated by limited supplies of elaborated foods, water, and possibly mineral nutrients.