Quality of wood of poplars used in the reclamation of spoil rock dump accompanying the lignite mining

The aim of the study was to determine quality of wood of 40−year old poplar cultivars introduced onto the external spoil dump of the Bełchatów Field and subjected to various reclamation systems. The research was carried out on the 1/78 trial plot located on the northern slope of the external spoil dump of the Bełchatów Field (central Poland). The dump was the result of the rock (predominantly sand) overlay storage accompanying lignite deposit. On the trial plot two blocks were established: one called ‘Humus’ where sandy sediments were covered with approximately 20−centimeter layer of fertile soil, and the other named ‘Piasek’ (sand) with only sandy sediments. To set up the experiment 9 poplar varieties were used (I−214, Robusta, Gerlica, H−194, Grandis, Oxford, Androscoggin, Geneva, H−275). Their wood quality was assessed in 2017, 40 years after their introduction on the spoil dump. The results indicate that poplars growing in the ‘Humus’ variant were characterised by higher volume in comparison to wood of poplars from the ‘Piasek’ variant. The latter however had a larger share of better wood quality classes (WB, WC). The results also showed that wood classification of all investigated varieties were significantly influenced by curvature in the case of the ‘Humus’ variant and knots in the ‘Piasek’ one. The influence of other wood defects such as galls, grain slope, multiple pith and knobs was insignificant. In order to obtain the higher volume of poplar raw material the reclamation treatments should be carried out on afforested areas with fertile outer layer whereas the better quality raw material can be obtained on less fertile sediments