Preliminary Results on the Effects of Initial Stand Density and Supplemental Irrigation on Biomass of Eucalyptus camaldulensis Dehn. Grown as a Short Rotation Woody Crop under Semi-Arid Conditions

Most short rotation coppice (SRC) plantations are grown in temperate, subtropical, and tropical areas where land availability is limited. Very little is known about the potential biomass yield of Eucalyptus camaldulensis grown as SRC under semi-arid conditions with supplemental irrigation. Our objective was to maximize biomass production of E. camaldulensis under semi-arid conditions as a feedstock for biofuels by optimizing initial stem density (ISD) and irrigation amount. We tested the effects of four densities of 2500, 10,000, 40,000, and 160,000 stems per hectare, and supplemental irrigation of 100% or 200% of potential evapotranspiration on tree growth and biomass production. Our results showed that under semi-arid conditions and supplemental irrigation, trees grew rapidly and accumulated biomass at a rate equal to or exceeding that in tropical regions. As ISD increased, individual trees grew slightly taller, became much narrower, and had fewer stems. We concluded that competition for resources such as light and nutrients increased with ISD, resulting in significantly lower biomass accumulation by individual trees. However, the significantly greater number of individuals with increasing ISD was responsible for the higher biomass production per hectare, allowing us to achieve exceptionally high annual yields of eucalypt biomass under semi-arid conditions after three annual coppicing cycles.