Investigation into the heterogeneous nature of the impregnability of some poplar hybrids
J Van Acker, M Stevens
Retention figures of some poplar hybrids are very heterogeneous when pressure impregnated. This makes it hard to prescribe impregnation processes for fast grown poplars that make it suitable for higher hazard uses. In order to gain fundamental knowledge in their variability in impregnation properties two trees were selected for a detailed investigation. Both trees originate from the same plantation and represent the genetically very similar clones Populus trichocarpa x deltoides 'Beaupre' and 'Boelare'. From the lower part of each stem a log was cut into over 80 samples measuring 5 x 5 x 100 cm³. After air-drying and conditioning they were CCA impregnated using a Lowry cycle. The mean retention levels for both trees are identical but their distribution in uptake figures is totally different. In the inner heart part of the 'Beaupre' tree the preservative liquid uptake of some samples was even lower than 90 kg/m³ while 'Boelare' samples at the corresponding location showed retentions of over 450 kg/m³. The differences in impregnation pattern are not related to the in-tree distribution of moisture content, density, radial/tangential sawing nor to the presence of tension wood. The hypothesis that parameters at the anatomical level affect the impregnability is examined and related to the specific type of heartwood present in poplar.