Effects of Fertilization and Thinning on Heartwood Area, Sapwood Area and Growth in Scots Pine

In a fertilization and thinning experiment on Pinus sylvestris L. situated in northern Sweden, the effects on the amount of heartwood and sapwood were examined 12 yrs after treatment. On stem discs taken from the stump up to 75% of tree height, age, diameter, heartwood diameter and growth rings included in the heartwood were measured. Increases in heartwood area following fertilization and thinning were not statistically significant, whereas sapwood area was significantly increased by both fertilization and thinning. There was a significant positive interaction effect of fertilization and thinning on diameter under bark, sapwood area and relative heartwood area. The number of growth rings included in the heartwood at breast height was not affected by treatments. Thinned trees showed a higher needle biomass per unit of sapwood area at breast height. The results show that the possibility of affecting the amount of heartwood in individual trees by thinning and fertilization is limited. The results are discussed in relation to the pipe - model theory and the regulation of sapwood and heartwood.