Abstract:

The transformation of sapwood to heartwood is an important physiological process in most tree species. Exploring the growth characteristics of heartwood/sapwood provides insights for understanding tree water relations，carbon metabolism，growth/yield modeling and wood use. In this paper，growth and development of heartwood and sapwood were studied for seven major tree species in northeastern China. They were Korean Pine (Pinus koraiensis)，Dahurian Larch (Larix gmelinii)，Japanese Elm (Ulmus japonica)，Manchurian Ash (Fraxinus mandshurica)，Manchurian Walnut (Juglans mandshurica)，Amur Corktree (Phellodendron amurense) and Mongolian Oak (Quercus mongolica). Ten trees for each species were sampled based on their diameter distribution. For each sampled tree，one disc every 1 m section along the bole was taken and determined for the width and rings of heartwood and sapwood with Windendro2003 (Regent Instruments Co.，Canada). The results indicated that tree species significantly (P<0.001) affected sapwood ring number (SRN) and sapwood width (SW). The mean SRN for Korean Pine, Manchurian Ash, Dahurian Larch, Manchurian Walnut, Japanese Elm and Amur Corktree were 9.6，9.5，7.9，6.8，5.0 and 3.9 a ，respectively; the mean SW were 1.96，1.27，2.55，1.06，0.72 and 0.46 cm，correspondingly. The SW for the conifers was overall greater than that for the broadleaved species. The heartwood ring number (HRN) was significantly positively correlated to cambial age (CA)， heartwood radius (HR) and SW were strongly positively correlated to xylem radius (XR). However，the relationship between SRN and CA was speciesdependent. The heartwood formation rate (HFR) and heartwood initiation age (HIA)，depending on tree species，varied from 0.677～1.041 a^-1and 4.3～8.5 a，respectively. As the tree height increased，the HR decreased，but the SRN changed with species. With an increase of tree height，the SRN for the Korean Pine decreased，and those for Japanese Elm，Manchurian Walnut and Amur Corktree showed little changes. The SRN for the Dahurian Larch increased initially and then decreased as the height increased，but that for the Manchurian Ash displayed an opposite pattern. The intra and interspecific differences in the growth and development of sapwood and heartwood may reflect their differences in growth pattern，production and water use strategies.

Key words: heartwood, sapwood, transformation of sapwood to heartwood, temperate forest