Environmental Engineering Reference
In-Depth Information
There will be a natural tendency to postpone the
switch as long as a less intensive arrangement will do.
This reality is illustrated by the lengthy coexistence of
foraging and cultivation. For example, at Tell Abu Hur-
eyra in northern Syria, hunting remained a critical source
of food for 1,000 years after the beginning of plant do-
mestication (Legge and Rowley-Conwy 1987). Another
example is the contrast between intensive farming in
plains and valleys and shifting cultivation in nearby
mountains, a contrast commonly seen in Southeast Asia
even in the second half of the twentieth century. Intensi-
fication advances in stages, from long forest fallow (just
one or two crops followed by a regeneration of 15-25
years), to bush fallow (with four to six crop years and a
similar fallow), to short fallow (a crop or two followed
by a year off ), to regular annual cropping (fallow reduced
to fall and winter) and finally, to multicropping, often
irrigated (two or three grain or oil crops, or five to six
vegetable crops, planted in rapid succession).
Each of these steps recovers more of the site's poten-
tial photosynthesis and supports more people per hectare
of land (fig. 6.1), but it demands higher energy inputs,
first for forest clearing, planting, and cultivation and
eventually for repeated cultivation, terracing, and irriga-
tion. These activities also require further energy invest-
ment for making tools and implements. And because a
large part of the energy inputs is in the form of long-
term investments (fields cleared of stones or terraced, ir-
rigation systems, roads), and intensive cropping needs
planning, storage, and trading, agricultural intensification
has been a key ingredient of a civilization's complexifica-
tion, promoting innovation, specialization, interdepen-
dence, and exchange of goods and techniques. And the
process led inevitably to reliance on sources of energy
other than human muscles. Plowing was either enor-
6.1 Ranges of population densities supportable by intensify-
ing modes of food provision.
mously taxing or outright impossible without draft
animals; manual threshing and milling of grains was so
labor-intensive that inanimate (water and wind) power
was necessary to process harvests for cities; long-distance
distribution of grain also relied largely on animal power
and wind; and iron for tools and implements was smelted
with charcoal.
6.1 Extensive Practices
Low population densities and abundant land availability
were the two key factors that favored extensive modes
of food production. Nomadic pastoralism and shifting
agriculture (slash-and-burn or fell-and-slash-and-burn
farming) are two very dissimilar practices sharing the
