Comparison of the productivity of Populus nigra L. with an interspecific hybrid in a short rotation coppice in marginal areas

Populus nigra as an autochthonous European woody species is irreplaceable in regions where it is not legal to plant allochthonous species. Twelve clones of P. nigra ssp. nigra and one clone NE-42 (Populus maximowiczii×Populus trichocarpa) were tested in two localities at altitudes of 515–600 m with annual temperatures 5.7–6.8 °C. Different cultural practices and nutrition were used in these localities. Rooted plants were set out (2222 plants ha−1). The second harvest was carried out after 4 years in a 7-year crop. The yield of the best clones of P. nigra (7.6–7.9 t ha−1 yr−1) approached the yield of hybrid clone (9.4 t ha−1 yr−1) in a fertilised locality, with pH=6.7 and lower rainfall amounts in the growing season. In a locality with pH=5, without fertilisation and with high groundwater level the yield of clones of P. nigra was 4.6–2.2 t ha−1 yr−1, in clone NE-42 it was 9.8 t ha−1 yr−1. The most productive clones of P. nigra had a significantly higher number of shoots (16.8–14.2) than the clone NE-42 (9.3) and the mortality of their shoots was lower (14–31.4%) than in NE-42 (32.1%). Shoots 20–53 mm in diameter accounted for 50% of the volume index of shoots in almost 70% of P. nigra clones. In high-yielding clones of P. nigra the dry weight of lateral shoots in total weight ranged between 66% and 75% while in NE-42 it was 55%. Resistance to Melampsora larici-populina Kleb. was higher in the interspecific hybrid but the best clone of P. nigra had a similar level of resistance.