Productivity of Populus nigra L. ssp nigra under short-rotation culture in marginal areas

P. nigra L. ssp. nigra as an autochthonous European woody species is irreplaceable in regions where it is not legal to plant allochthonous species. Its productivity is not known. Twenty-nine clones of P. nigra ssp. nigra, two clones of P. x euroamericana and clone NE-42 (P. maximowiczii x P. trichocarpa) were tested in three localities at altitudes of 515 -600 m with annual temperatures 5.7-6.9degreesC and soil reaction 5.0-6.7 pH/CaCl2. Different cultural practices and nutrition were used in the localities. Rooted plants were set out (2222 plants/ha). Harvest was carried out 3 years after planting. The best clones of P. nigra were equal in performance to clone NE-42 (1.4 t ha(-1) yr(-1) biomass) in the locality with highest nutrient content, highest pH (6.7) and lower water content. On soils with low pH (5.0) P. nigra clones were worse than NE-42, but better than cv. Robusta. The initial faster growth of P. nigra clones was surpassed by the growth of clone NE-42 in the third year. The numbers of shoots after harvest were 12.8-25 shoots per plant in P. nigra clones, 13.7 in NE-42 and 12.1 in P. x euroamericana. Resistance to Melampsora larici-populina was higher in interspecific hybrids but the best clone of P. nigra had similar resistance as interspecific hybrids. The heat of combustion in NE-42 and 210 amounted to 19.27 and 18.76 kJ g(-1). The highest dry matter content and combustion heat was found for branches, the lowest for stern base. The results suggest that selected clones of P. nigra can be successfully used in the regions where autochthonous species must be planted. (C) 2002 Elsevier Science Ltd. All rights reserved.