Environmental Engineering Reference
In-Depth Information
In low-income countries the greatest savings of natural woody phytomass could
come from the combination of four key strategies: the adoption of efi cient rural
stoves (such as those that are now widely used in China), a substantial reduction
of illegal logging, a major expansion of suitable tree plantations, and the willingness
of afl uent countries to subsidize effective protection of the richest forest ecosystems
in well-managed national parks. In high-income nations the most obvious routes
toward reduced wood consumption are whole-tree utilization and the expanded
production of engineered timber (Williamson 2001), higher rates of paper recycling
(McKinney 1994), and a further shift from paper-based i les to purely electronic
records.
Because of the importance of agriculture in ecosystem transformations, the net
outcome will depend largely on the countervailing effects of cropping intensii cation
(higher yields requiring smaller planted areas) and a rising demand for food and
feed crops (owing to the increasing global population and the worldwide dietary
transition and higher demand for animal foods). Cropping intensii cation—not only
higher yields and more frequent multicropping, but more recently also a greater
extent of more energy- and labor-intensive cultivation in greenhouses or under plastic
shields—has been the key reason limiting the demand for new cultivated land.
With average crop yields remaining at the 1900 level, the crop harvest in the year
2000 would have required nearly four times more land, and its total (nearly 60
Mkm
2
) would have claimed nearly half of all ice-free continental area rather than
less than 15% the agricultural lands claim today. A different perspective has been
quantii ed by Burney, Davis, and Lobell (2010): they calculated that between 1961
and 2005, increased crop yields had a net effect of avoiding emissions of up to 161
Gt C. There is no doubt that this intensii cation will continue virtually everywhere,
but its national and regional rates will continue to differ.
Most of the world, and Africa in particular, has average crop yields well below
realistically achievable performance: Africa's recent average yields for corn, sorghum,
and wheat have been 65%, 30%, and 25% below their respective global means
(FAO 2011d). And even the most intensively farmed countries, whose best yields
are much closer to the highest recorded rates, can do better (Sylvester-Bradley and
Wiseman 2005). For example, even in the UK, where the average yield of wheat
(main staple grain) is already high at 7.7 t/ha and that of rapeseed (main oil crop)
is 3.2 t/ha, the application of management and genetic improvements based only on
existing knowledge could raise these means to, respectively, 8.7 and 3.9 t/ha (Spink
et al. 2009). Even then the long-term possibilities for genetic engineering would
