VEGETATIVE AND REPRODUCTIVE GROWTH OF BLACK SPRUCE (PICEA MARIANA (MILL.) BSP.) AT CHALK RIVER, ONTARIO, CANADA

Apical growth of the leader and lateral branches, as well as radial increment at the top and bottom of the trunk, were studied in two black spruce trees during 1960–63. The study complemented that of the developmental anatomy of shoot tips from adjacent trees during the period 1955–62. Time of initiation of apical growth varied from the third week of May in 1960, 1962, and 1963 to early June in 1961. The termination period of apical growth extended from early July in the lower branches, until about 2 weeks later in the upper branches and leader. Radial increment in the trunk started at about the same time as bud swelling and continued into August. A temporary mid-summer cessation of radial increment occurred at the top of the tree in two consecutive years. The response to artificially induced short and long days from May to August in 12-year-old saplings indicated that initiation of apical growth is not affected by photoperiod. Short days were associated with a reduction in apical extension, needle length, and growth period.Reproductive buds could be recognized by early August, but the formation of ovuliferous scales or pollen sacs did not occur until several weeks later. The male cones differentiated about 1 week before the female ones. The consistent production of flower buds in black spruce compared to the sporadic formation in white spruce is partly attributed to the difference in time of initiation of apical growth. In black spruce the development of buds occurs about 2 weeks later, usually during a warmer part of the summer when conditions are considered more conducive to reproductive growth.