Irregular heartwood formation in Pinus pinaster Ait. is related to eccentric, radial, stem growth

Abstract

In order to determine whether the distribution of heartwood in Maritime pine, Pinus pinaster Ait., is affected by stemlean stem, cross sections of trunks at different heights were taken from fifteen 52-year-old leaning trees (angle of lean varied from 0 to 20°). Cross sections were found to be eccentric in shape. However, this eccentricity was not correlated to tree lean, but was related to wind direction. Heartwood was not found to form regularly with tree age and its production regressed significantly with stem eccentric growth. A significantly larger number of annual rings were transformed into heartwood on the compression (underneath the lean or leeward) side of the tree than the opposite or perpendicular sides of the tree. The proportion of heartwood was found to be significantly smaller at the base of the tree, where it accounted for 45% of the cross section, compared to further up the tree at 2.5 and 5.0 m, where it accounted for 57% of the cross section. The proportion sapwood:heartwood remained constant around the cross section, regardless of the direction of lean or wind. Therefore, early heartwood formation on the compressed sides of leaning trees may be due to a developmental process, which allows the tree to maintain a constant, optimal volume of sapwood around the trunk. Further investigations into the physiological and biochemical changes incurred during heartwood formation are needed to explain this phenomenon.