The effect of cutting back willow after one year of growth on biomass production over two harvest cycles

Trials were conducted on four separate but adjacent blocks of willow at a site near Carlow, Ireland in which willow, after one growing season, was either coppiced or left to grow. Each of the four randomised complete block design trials contained a different willow genotype (Endeavor, Resolution, Terra nova and Tordis). Coppicing had no adverse effect on stool mortality but significantly increased the number of stems per stool from 2.0 to 3.3. The average, median and maximum diameters of stems from non-coppiced stools were significantly greater than those of stems from coppiced stools. Biomass from non-coppiced treatments was significantly greater than that from coppiced treatments both one year after coppicing (4.3 Mg/ha [coppiced]; 9.3 Mg/ha [non-coppiced]) and two years after coppicing (12.6 Mg/ha [coppiced]; 20.8 Mg/ha [non-coppiced]). Both coppiced and non-coppiced treatments were harvested two years after coppicing and left to grow for an additional two years. After this two year period, there was no significant difference in stem numbers per stool, stem diameter and biomass yield between the coppiced and non-coppiced treatments. All willow genotypes responded in a similar way to coppicing. The results suggest that the omission of the coppicing operation after one year of growth may increase biomass yield at the first harvest without compromising yield at the second harvest.