The idea of cultivating trees strictly for energy and biorefining purposes has been proposed. Certain fast growing tree species such as cottonwood, aspen and eucalyptus can grow at rates of around 1 m/yr or even more. The short-rotation woody crop (SRWC) technique can be used to reach yields of about 10 dry metric tons of woody crops per hectare per year can be achieved. However, the economic viability of SRWC is very fragile due to the high costs of preparation and fertilization of the sites [19].

Depending on the maturity of the woody crops, chemical composition will remain close to that of wood and bark (see Sect. 11.2.1.1). The main difference will arise due to the leaves and trimmings, which will accumulate dust and metabolic inorganics up to a few mass per cent during the trees’ growth.

11.2.1.3 Perennial Herbaceous Crops

Perennial crops are vegetal—not edible for humans—which include among others: switchgrass, weeping lovegrass and Napier grass. Herbaceous crops are usually dedicated to alcoholic fermentation because of their high availability of complex sugar content, but pyrolysis of these vegetals has been shown to produce high oil yields [20]. The oil produced contained water-soluble and water-insoluble fractions. Moreover, significant amount of alkanes and phenolic compounds can be found in these oils [21] suggesting a high potential of perennial crops for specialty chemicals production from pyrolysis.