Optimum cutting cycle and plantation design were the focus for studies with three fast­growing clones at three locations in the United Kingdom. Populus trichocarpa was evaluated at two spacings (1.0 x 1.0 m and 2.0 x 2.0 m) and two — or four-year cutting cycles [51]. Annual yield of biomass was always higher in the longer cutting cycle and the 1 m2 spacing generally had a higher biomass yield than the 4 m2 option. The authors pointed out that all poplar cones gave higher yield at the site with the highest annual rainfall. They also suggested that the reason for better yields with the longer cutting cycle was a proper balance between root system and aboveground organ development. The authors also noted that a four-year cutting cycle is more economical due to lower harvest cost per unit dry matter.

di Nasso et al. [52] pointed out that plant spacing and cutting cycles are the most crucial factors for successful establishment and biomass production by short-rotation poplar. Their report summarizes results of long-term studies (12 years) designed to identify the most important production indices in relation to different cutting cycles (from annual to triennial). They found that the shortest cutting cycles resulted in increased stool mortality, making the shortest cutting cycle less efficient than the other cycles studied. The highest efficiency in terms of energy output was noted for a triennial cutting cycle. The authors stated that the energy balance was positive for all studied cutting cycles and that for short-rotation plantations good soil fertility plus low rates of fertilizer and pesticide application were important for making short-rotation poplar plantations a perfect example of sustainability in twenty-first century agriculture.

Fang et al. [53] also tested four planting densities and three poplar clones at three cutting frequencies. Each of the experimental factors significantly affected obtained biomass yield, with the highest annual production being obtained with a six-year cutting cycle. They concluded that, for China, a longer cutting cycle should be recommended because regardless of plant density biomass yield increased as cutting cycle length increased (i. e. from 10 to 13 Mg ODM ha-1 yr-1 when going from a four to six-year cutting cycle).

Guidi et al. [54] quantified the relationship between chemical composition of biomass obtained from SRP poplar and cutting frequency of plantations in order to answer the crucial question of “how to manage the plantation to achieve good quality of biomass for biochemical conversion into liquid biofuels.” They concluded that different cutting cycles did influence the biochemical conversion rate of the poplar biomass, with the highest ethanol yield being associated with a four-year cutting cycle. This occurred because, at that age, the relative content of cellulose was much higher than in poplar biomass obtained from two-year cutting cycles, when the hemicellulose content was higher, or from six-year cycles, when the lignin content was greater because of the additional two years of growth.