Environmental Engineering Reference
In-Depth Information
emissions, nutrient runoff, pesticide runoff, and land-use impacts). In the long run,
developing a broad range of grassy crops for energy use is compatible with both sus-
tainability and economic viability criteria.
Short-rotation woody crops
(SRWCs) represent another important category of
future dedicated energy crops. Among the SRWCs, hybrid poplar, willow, American
sycamore, sweetgum, and loblolly have been extensively researched for their very
high biomass yield potential. Breeding programs and management practices con-
tinue to be developed for these species. SRWCs are based on a high-density planta-
tion system and more frequent harvesting (every 3 to 4 years for willow and 7 years
for hybrid poplar). Following is a summary of short-rotation crops:
•
Hybrid poplar
—This species is very site specific and has a limited growing
niche. It requires an abundant and continuous supply of moisture during
the growing season. Soils should be moist but not continually saturated
and should have good internal drainage. It prefers damp, well-drained, fine
sandy-loam soils located near streams, where coarse sand is first deposited
as flooding occurs. Hybrid poplars are among the fastest-growing trees in
North America—in just six growing seasons, hybrid poplars can reach 60
feet or more in height. They are well suited for the production of bioenergy,
fiber, and other biobased products.
•
Willow species (Salix)
—In folklore and myth, a willow tree is believed to
be quite sinister, capable of uprooting itself and stalking travelers. The real-
ity is that willows are used for biofiltration, constructed wetlands, ecologi-
cal wastewater treatment systems, hedges, land reclamation, landscaping,
phytoremediation, stream bank stabilization (bioengineering), slope stabili-
zation, soil erosion control, shelterbelt and windbreak, soil building, soil rec-
lamation, tree bog composting toilets, and wildlife habitat. Willow is grown
for biomass or biofuels in energy forestry systems as a consequence of its high
energy-in/energy-out ratio, large carbon mitigation potential, and fast growth
(Aylott, 2008). Willow is also grown and harvested for making charcoal.
•
American sycamore
—Sycamores prefer alluvial soils along streams in bot-
tomlands. Sycamore growth and yield are less than those of poplars and
willows.
•
Sweetgum (Liquidambar styracilua)
—Sweetgum is a species tolerant of a
variety of soils, but it grows best on rich, moist, alluvial clay and loam soils
of river bottoms.
•
Loblolly pine
(Pinus taeda)
—Loblolly pine is quite adaptable to a variety
of sites. It performs well on both poorly drained bottomland flats and mod-
estly arid uplands. Biomass for energy is currently being obtained from
precommercial thinnings and from logging residues in loblolly pine stands.
Utilization will undoubtedly increase, and loblolly pine energy plantations
may become a reality.
In many parts of the country, plantations of poplar, willow, pines, and cottonwood
have been established and are being commercially harvested. Willows are being
planted in New York, particularly following enactment of the Renewable Portfolio
