Frequency of False Heartwood of Stems of Poplar Growing on Farmland in Sweden

Swedish owners of poplar stands are interested in both the wood quality and the use of poplars that are soon to be harvested. An important concern is the frequency of false heartwood (FHW) in the stems. We have presented an overview of the factors causing discolored wood as well as the industrial use and quality of the end products. We have studied poplar stems growing at 22 sites in Sweden between latitudes 55° N and 60° N. The mean age of the poplar was 23 years (range 14–41), the mean stand density 1011 stems ha (range 155–3493) and the diameter at breast height (DBH) (over bark) 246 mm (range 121–447). All stands were growing on clay soils (light and medium clay and light clay tills). All of the sampled stems (42) contained false heartwood. At 0%–50% of stem height, all sampled trees were discolored and at 90% of stem height, 33% were discolored. The percentage of false heartwood area by stem area was highest at 1% and 10% of stem height (26.6% and 24.7% respectively). The “FHW” part of the stem had a radius of 47 mm (range 9–93) at 30% of stem height, which corresponds to 50% of the total stem radius. A log of six meters represents about 30% of stem height. Equations describing the correlation between DBH and the diameter of FHW at different stem heights (1%, 10%, 30%, 50%, 70% and 90%) and table describing FHW volume % by total stem volume at the first 50% of stem height were constructed. These might be helpful for estimating the percentage of fresh wood in a stem. However, most of the fast-growing poplars will be harvested as biofuel.