Growth patterns of Slash and Caribbean Pine and their hybrids in Queensland

Summary Seasonal height and girth growth patterns of hybrids between Slash Pine (Pinus elliottii Engelm. var elliottii L. & D.) and Caribbean Pine (Pinus caribaea Mor. var hondurensis B. & G.) were compared with those of the parental species over one year at Beerwah Forest in southern coastal Queensland, Australia. The parental growth patterns differed markedly. Slash Pine had very vigorous early season growth, the rate then declined steadily through the later part of the season until the species entered winter dormancy. Caribbean Pine grew steadily throughout the year with late summer the most active period and winter the least. The hybrids combined the parental growth patterns with a consequent vigour advantage.Slash Pine showed a high degree of stem to stem synchronization of height growth in the early season, but much less in the later part, whilst height growth of Caribbean Pine was totally asynchronous. The hybrid was intermediate in stem to stem synchronization.The number of branch whorls produced by individual trees of Slash Pine on the main stem in the season 1965–1966 were found to be directly related to the length of the growing season for the tree concerned and also to the total height of the tree. Counts on trees at various centres in Queensland showed a decrease in branch whorl number per season with movement northwards suggesting a decrease in the length of the growing season of the species at lower latitudes. Possible physiological reasons for this are discussed.