HEART SHAKE IN SOUTH AFRICAN - GROWN PINUS ELLIOTTII ENGELM.; ITS DISTRIBUTION AND ORIGIN

Heart shake, internal cracks in the radial and longitudinal planes of standing trees, is the most common and serious defect of South African-grown Pinus elliottii.;The conclusions of this thesis are: (1) Heart shake was found in all locations sampled. Although the frequency of occurrence of heart shake did not vary much among locations, the severity of heart shake damage did. (2) Within trees most of the heart shake found were located in the butt end of the tree and extended downward into the stump. (3) No tree physical characteristic or environmental factor could be associated with the incidence of heart shake although rate of growth and exposure to strong winds did influence the severity of the heart shake in a tree. (4) There is a possibility that there are genetic differences in the incidence of heart shake among families of Pinus elliottii. (5) Heart shake is initiated in a tree by the wounding of that tree in various ways, particularly by mechanical damage during the nursery and field planting stages. Damage to the root collar zone causes a point of weakness that enlarges longitudinally and radially into a heart shake as the tree grows. (6) There are very large differences among trees in the severity of heart shake and degree of resinosis associated with heart shake that cannot presently be explained.;This thesis describes a series of experiments that sampled immature and mature trees throughout the Eastern Transvaal Forestal Region of South Africa. The objectives of these studies were to determine: (1) the distribution of heart shake within and among trees; (2) whether any tree physical characteristics or environmental factors were associated with heart shake; (3) the age at which heart shake begins; and (4) the factors that initiate heart shake.