The human ecology of climate change - Climate Change: Biological and Human Aspects - page 437

some may be predominantly one or the other. Miscanthus , for instance, is also being
investigated as a possible UK crop for fibre production. Birch ( Betula spp.), willow
( Salix spp.) and alder ( Alnus spp.) can contribute to biofuel production while con-
tinuing to provide stock for paper and fibre-board production. Since these are broad-
leaved, woody species, their appropriate cultivation adds substantially to the biod-
iversity of associated flora and fauna and offers visually attractive amenities during
production.
As to the potential contribution of biofuels, taking the UK at the turn of the millen-
nium as an example, if all 500 000 ha of UK set-aside land (farmland deliberately not
used for agriculture, equivalent to 3% of the land within agricultural holdings) was
planted with, for instance, Miscanthus , and assuming a median dry-matter production
of 15 t ha − 1 year − 1 and a broadly typical 40% conversion to oil in energy-content
terms, then some 3 mtoe of biofuel would result. This would be equivalent to nearly
4% of UK end-20th century/early-21st-century annual oil demand. If Miscanthus oil
production could be increased to an optimistic 25 t of dry matter ha − 1 , then more
than 6% of UK oil demand would be met. However, Miscanthus does not reach its
peak yields until the third or fourth season, even though absolute peak yields for
Miscanthus sacchariflorus of 44 t of dry matter ha − 1 year − 1 have been reported from
Denmark. This peak, if possible across all such potential UK Miscanthus production,
would result in 14 or 15 t of oil ha − 1 year − 1 . However, such high yields are highly
theoretical and cannot be considered a realistically obtainable national average at
this time (Cowie, 2003), although they might with appropriate breeding or genetic
modification if environmental concerns could be addressed.
A similar calculation for oilseed rape would take into account the approximately
3.2 t harvested per hectare (in the UK), the 37% of recoverable oil from the rapeseed
and the 95% conversion to diesel. This gives us about 0.4 mtoe year − 1 (0.5% of
UK oil demand around the turn of the millennium). The advantages of rapeseed are
that the plant's entire life cycle takes place in the UK, but has the disadvantages that
methanol (equivalent to about 12% of fuel yield) is required during the diesel-making
process; however, this methanol could come from biological sources too. It should be
noted that there are rotational constraints on rapeseed production: rapeseed is usually
grown one year in five in the UK.
Miscanthus and rapeseed oil are taken as just two examples of how currently
unused set-aside land could contribute to make the UK more energy-secure through
increasing energy self-sufficiency. However, it may be that some other crops, or crop
mix, would be preferable. Climate conditions do not favour Miscanthus rhizome
production in Europe as they do in the tropics. Nonetheless, rhizome production is
possible in the UK (which is warmed by the Gulf Stream) and in some other parts
of Europe. Consequently, the examples are illustrative and the production levels of
Miscanthus and rapeseed oil are not atypical in energy terms of other biofuels.
It should be noted that in addition to the 3% of land within agricultural holdings
being set aside, 97% is not. (Of this 24% is rough grazing and 11% unspecified.
Indeed, of the 97% of agricultural land that is not set aside, only 25% is used
for crops.) In short, there is room for some considerable increases in the land that
might be available for biofuels. Assuming, solely for purposes of example, that 6%
of current UK oil consumption was met through the use of specific biofuel crops,