Environmental Engineering Reference
In-Depth Information
in the tropics: a major share is obviously emitted as CO
2
, but inefi cient combustion
and smoldering i res also produce CO. Moreover, under some conditions a signii -
cant share of phytomass carbon turns into biochar (charcoal produced at low
temperature), a material that can remain intact in soils for several hundred to a few
thousand years, providing a long-term sequestration of the element while improving
soil quality and enhancing primary productivity. Anthropogenic Amazonian
terra
preta
(black earth) soils, created by surprisingly dense late prehistoric (600-1200
CE) settlements scattered throughout the region (Heckenberger et al. 2003), are the
best-known example of this counterintuitive outcome when wood burning results,
at least partially, in the prolonged storage of carbon.
Nobody in a modern economy is now converting forestland to cropland by
burning, and shifting cultivation relying on periodic burning today produces only
a very small share of the worldwide food output. But during the last two decades
of the twentieth century satellite monitoring illustrated the extent of i res used to
clear forested land to create new i elds and pastures and for transportation, settle-
ments, and industrial uses throughout Latin America and Southeast Asia, particu-
larly in the Brazilian Amazon and parts of Indonesia (Levine 1991; Bowman et al.
2009; Lauk and Erb 2009). Satellite images also show i res set to stimulate pasture
regeneration during the late summer months across the Sahel, from Senegal to
Eritrea, and in an even broader swath of land extending across the southern part
of the continent from Angola to Mozambique (Barbosa, Stroppiana, and Grégoire
1999; Roberts, Wooster, and Lagoudakis 2009). Grasslands, too, are often burned
in Central America, parts of India, and Southeast Asia.
As decades of burning were reducing the area of tropical rain forests, an opposite
trend in land-cover change began to accelerate in many afl uent countries in the
temperate zone. Higher crop yields and the consolidation of farming in the most
suitable regions led to a widespread abandonment of marginal cropland and its
gradual reforestation. This trend has been most notable in eastern North America
and in more than half of all European countries. The conversion of suburban agri-
cultural land to residential, commercial, and industrial uses and the growth of
transportation corridors have been affecting primary production all around the
world, particularly in the rapidly urbanizing societies of Asia and Latin America.
But not everything is lost: lawns and city parks maintain, and in patches can even
surpass, previous primary productivity.
A curiously neglected consequence of unplanned or poorly planned urban and
industrial expansion has been the fragmentation of land use, a worldwide phenom-
enon with a substantial aggregate impact on primary productivity. This expansion
