Variation of wood basic density and early selection of dahurian larch and Mongolian pine

The sample data was from dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica) mature plantations located in Qitaihe Forest Bureau in Heilongjiang Province,northeastern China.Wood disks of 5 cm thick were taken at ground,1.3 m,20%,40%,60%,80% of the total height from each tree. A wedge was cut from each sample disc along the south radius. Each wedge was divided into 8 equal parts along the radius. Wood basic density of each part was obtained using water displacement method. Variations of wood basic density within tree, among trees, from pith to bark, from base to the top of tree and correlation of wood basic density within ring groups were investigated using variance analysis, multiple comparison, correlation analysis, and regression analysis methods. The results showed that variations of wood basic density were noticed within-tree for dahurian larch and Mongolian pine. There were significant variations among trees and radial variations along the tree stem.Wood basic density decreased from the stump to top of the tree for dahurian larch.However,wood basic density decreased from stump to 20% of total height, and then increased towards the top of stem. Correlation analysis of wood basic density among age groups showed that dahurian larch trees with slow growth could be removed at early stage. Trees could be selected based on wood basic density during 5-10 years.However,Mongolian pine could be selected based on wood basic density at early stage.