Research Crown Diameter and Diameter at Breast Height Relations of Ten Kinds of Major Natural Secondary Broad-leaved Tree in Maoershan PRELIMINARY STUDIES ON RADIAL VARIATION PATTERNS OF WOOD PROPERTIES WITHIN TREES-Ⅲ.STUDIES ON THE EFFECT OF TREE SPACING ON THE RADIAL VARIATION PATTERNS OF WOOD DENSITY IN SLASH PINE AND LOBLOLLY PINE