Biomass production of Populus nigra L. clones grown in short rotation coppice systems in three different environments over four rotations

Three clones of black poplar and a hybrid poplar clone, “NE-42”, were trialled in a short rotation coppice system. The trial was replicated in three sites located in the Czech Republic with distinctly different soils and climates which were judged to be respectively favorable, unfavorable and marginal for growing black poplar. In the marginal and unfavorable sites the planting density was 2222 trees ha-1 and in optimal conditions 7407 trees ha-1. The aim of the trial was: (1) to test the performance of black poplar clones as a possible replacement for commercial hybrid poplars in areas where the genetic integrity of wild black poplar populations is under threat; (2) to test the range of conditions in which it is possible to grow black poplar and its suitability for utilizing marginal agricultural land; and (3) to measure the potential yield of black poplar clones grown in these conditions. During four harvests at three-year intervals, the following parameters were measured: plant mortality, number of shoots, thickness of shoots, the total cross-sectional area (TCA) of all shoots, the dry matter weight of individual plants (DMIP) and the dry matter yields per hectare. The differences observed between “NE-42” and the best black poplar clone decreased as conditions became more favorable. During the fourth harvest at the unfavorable site for growing poplars, the yield of dry biomass was 11.7 t ha-1 yr-1 for “NE-42” compared to 3.7 t ha-1 yr-1 for the best black poplar clone. In marginal conditions the yields were 11.8 and 9.9 t ha-1 yr-1 respectively, and in the favorable conditions there was no statistically significant difference, being 15.9 and 13.2 t ha-1 yr-1, respectively. The higher yield of “NE-42” was due to the higher proportion of thicker shoots or, alternatively, lower plant mortality. The observed TCA was highly correlated with DMIP (rs = 0.87) and dry biomass yield (rs = 0.48). It was demonstrated that black poplar can be successfully grown in marginal conditions on land which otherwise would not be especially suitable for agricultural production, and also in areas where the genetic purity of native populations of black poplar is threatened by the spread of commercially grown hybrid poplars