Harvesting System Design and Performance - Engineering and Science of Biomass Feedstock Production and Provision - page 109

Fig. 5.26 Functional processes in harvest and transport of short rotation woody crops

5.4.2 Short Rotation Woody Biomass Crops

Woodycropswithstemdiameterlessthan80mmaretypicallyclassiiedasshortrota-
tionwoodcropsthataregrownonagriculturallands.Willowandpoplararethetwo
candidatecropsworldwide,andthemachineryusedtoharvestthemissimilar.Willow
harvesting is carried out when leaves have fallen from the willow stems. In North
America, the harvesting period varies from the end of November until April. The
moisturecontentisabout55-60%whenthewillowisharvested.Sincewillowstools
are more aggressive and can puncture tires, forest-based machinery tires that have
tougher side walls are often used. The cutting devices may be redesigned so that they
do not leave stubble which can puncture the tires of machines following the harvest.
Figure 5.26 shows functional processes in harvest and transport of woody biomass.

5.4.2.1 Two-Pass Harvesting of Short Rotation Crops

The first option in two-pass harvesting is whole stalk harvesting and chipping.
Wholestemsarecut(Fig. 5.27a ) and chipped wet or after natural drying (see
Fig. 5.27b ).Chippingofdriedwholeshootsisdificultbecausedryingmakesthe
shoots brittle. Also, small side twigs break off easily during handling, and a large