Evaluation of Four Poplar Clones in a Short Rotation Forestry in Central Italy

Two field experiments were carried out in 2006 and 2007 in central Italy (42°57’N, 12°22’E, 165 m a.s.l.) in order to investigate the influence of site, planting densities/spacings and cutting cycles on the biomass production of four poplar clones [(Populus – generosa) – Populus nigra “Monviso” and “AF6”, Populus – canadensis “AF2”, Populus deltoides – Populus – canadensis “SIRIO”] selected for SRF. Hardwood cuttings of each clone were planted at two different densities and planting designs: a) low density = 5500 cuttings ha-1 were placed in a single-row design; b) high density = 11000 cuttings ha-1 were placed in a coupled-row design, and were tested with two cutting cycles: one-year cycle and two-year cycle. The experimental design was a split-plot with three replicates. The initial survival of clones was recorded after the establishment period. The number of shoots per plant (stool) was determined after the first growing season. Plant height (height of the main stem), main stem diameter at a height of 1 m and of 1.3 m above the ground and biomass production were measured from each plot, every year at harvesting time at the end of the growing season. Plant samples were also taken in order to assess humidity content, lower and higher heating values (LHV and HHV) and ash content of poplar biomass. All poplar clones showed a very high stool survival with values ranged from 95% to 99%. Monviso and AF2 can be advisable thanks to the higher biomass production than AF6 and Sirio. Considering planting density, low density (5500 plants ha-1) seems to be more advisable than high density (11000 plants ha-1) in order to obtain good biomass production with low planting cost. Considering cutting cycles, two-year cutting cycle allows higher biomass production (5.8 odt ha-1 year-1) than oneyear cutting cycle (4.7 odt ha-1 year-1), regardless of clones or density. Concerning main stem height and diameter some interesting equations were found in order to explain the relationship between them or with biomass production. In particular, a functional relationship between dry biomass production and stool diameter, appropriate for this climatic area and environmental conditions, was found. Analysis concerning wood energy content showed a good quality of poplar biomass thanks to high HHV and LHV values (an average of 19.7 MJ Kg-1 and 19.4 MJ Kg-1), low ash content (an average 3.6%) and low biomass humidity at harvest (an average 54%).