Editing Conifer (section)

==== Tree development ====
The growth and form of a forest tree are the result of activity in the primary and secondary [[meristem]]s, influenced by the distribution of photosynthate from its needles and the hormonal gradients controlled by the apical meristems.<ref name="Fraser-1964">{{cite journal|last1=Fraser|first1=D.A.|last2=Belanger|first2=L.|last3=McGuire|first3=D.|last4=Zdrazil|first4=Z.|year=1964|title=Total growth of the aerial parts of a white spruce tree at Chalk River, Ontario, Canada|journal=Can. J. Bot.|volume=42|issue=2 |pages=159–179|doi=10.1139/b64-017 |bibcode=1964CaJB...42..159F }}</ref> External factors also influence growth and form.

Fraser recorded the development of a single white spruce tree from 1926 to 1961. Apical growth of the stem was slow from 1926 through 1936 when the tree was competing with [[herb]]s and [[shrub]]s and probably shaded by larger trees. Lateral branches began to show reduced growth and some were no longer in evidence on the 36-year-old tree. Apical growth totaling about 340 m, 370 m, 420 m, 450 m, 500 m, 600 m, and 600 m was made by the tree in the years 1955 through 1961, respectively. The total number of needles of all ages present on the 36-year-old tree in 1961 was 5.25&nbsp;million weighing 14.25&nbsp;kg. In 1961, needles as old as 13 years remained on the tree. The ash weight of needles increased progressively with age from about 4% in first-year needles in 1961 to about 8% in needles 10 years old. In discussing the data obtained from the one 11 m tall white spruce, Fraser et al. (1964)<ref name="Fraser-1964" /> speculated that if the photosynthate used in making apical growth in 1961 was manufactured the previous year, then the 4&nbsp;million needles that were produced up to 1960 manufactured food for about 600,000&nbsp;mm of apical growth or 730 g dry weight, over 12&nbsp;million mm<sup>3</sup> of wood for the 1961 annual ring, plus 1&nbsp;million new needles, in addition to new tissue in branches, bark, and roots in 1960. Added to this would be the photosynthate to produce energy to sustain respiration over this period, an amount estimated to be about 10% of the total annual photosynthate production of a young healthy tree. On this basis, one needle produced food for about 0.19&nbsp;mg dry weight of apical growth, 3&nbsp;mm<sup>3</sup> wood, one-quarter of a new needle, plus an unknown amount of branch wood, bark and roots.

The order of priority of photosynthate distribution is probably: first to apical growth and new needle formation, then to buds for the next year's growth, with the cambium in the older parts of the branches receiving sustenance last. In the white spruce studied by Fraser et al. (1964),<ref name="Fraser-1964" /> the needles constituted 17.5% of the over-day weight. Undoubtedly, the proportions change with time.