The Period of Height Growth in Some North‐Eastern Conifers

In studying the reactions caused in plant communities either by the plants themselves or by external agencies, it is of interest and value to follow as closely as possible the phenomena of growth under various conditions. Especially is this true of forest vegetation where growth is of so great commercial importance. In the present instance attention has been directed to certain conifers, which, because of their present importance to the paper and pulp industry, it is most desired to perpetuate in the forests under consideration. Tree growth may be observed and measured in many forms. In the earlier stages of development height growth suggests itself as convenient to measure, and, in degree as the species is sensitive in response, is an excellent indicator of the effect of different treatments, such as release cuttings, trenchings, etc. In other words, individual plants may be measured to determine the growth rate of that species of plant under the given conditions, or the plants may be considered in the nature of phytometers, indicating quantitatively the effect of external factors. Specifically, height growth in the seed-% ling stage often determines whether or not a young tree will be able to survive and outstrip competitors of the same and other species. Competition for growing space is particularly intense among the invading vegetation following such severe disturbances as fire and lumbering. Like the time of germination, the period during which height growth takes place each season may have an important bearing on the ability of a species to attain dominance. In any investigation involving the growth of forest trees, such as a study of volume increment, whether by permanent or temporary sample plots, it is of importance to take the necessary measurements at a time when growth is not in progress. This presupposes a knowledge of when such growth takes place. Seeding, planting and transplanting operations should also be timed with regard to the natural period of growth (Watson, '20). The times of beginning and ending growth may also be significant in the choice of seed of local races for planting in a different region. Again, the seasonal habits of certain insects seem to be correlated with the course of height growth of the trees they attack. A knowledge of the latter may be of value in the