Environmental Engineering Reference
In-Depth Information
Ramankutty and Foley (1999) ended up with 400 Mha for 1700 and 820 Mha
for 1850, while Klein Goldewijk (2001) used a Boolean approach (based on
available statistics and maps of natural potential land cover) to generate distribu-
tions of croplands, grasslands, and natural ecosystems and came up with the same
values as Richards (1990). Pongratz et al. (2008) used historical maps of agricultural
areas and population data as a proxy for farming activities to estimate that about
500 Mha of natural vegetation were transformed to cropland (slightly more than
half of that total mainly by conversion of forests) and pastures (mainly by conver-
sions of natural grasslands) between 800 CE and 1700. And Kaplan, Krumhardt,
and Zimmermann (2009) developed a historical model of European deforestation
according to which between 70% and 95% of land available for clearing for agri-
culture in Central and Western Europe had forest cover in the year 1000 (ranging
from 95% in Poland to 69% in Italy), but by 1850 that share was generally below
10% (6% in France, only 3% in Germany).
The latest and the most systematic of these reconstruction efforts—HYDE 3, by
Klein Goldewijk and van Drecht (2006)—modeled the changes in land use and land
cover by using the distributions of population density, land suitability, distance to
major rivers, and natural vegetation cover. Its global totals for cropland begin in
5,000 BCE with about 5 Mha, rise to about 130 Mha at the beginning of the
Common Era, reach only a bit over 150 Mha a millennium later, and double to 300
Mha by the year 1700. These data address the problem of the inherently large errors
of all pre-1800 estimates by offering not only the most likely totals but also a low
and a high estimate: for the year 1700 the range was
±
25% around the preferred
base value, in 1800 it was about
18%, by 1900 the differences were -10% and
+22%, and the ranges changed little even by 1950, to -8% and +16% (HYDE
2011).
The productivity gains of the early modern era could not satisfy the additional
food and feed requirements resulting from higher population growth rates, continu-
ing urbanization, slowly improving diets, and a larger number of draft animals. As
a result, the expansion of farmland began to accelerate during the eighteenth century
(in some countries already after 1600), and the nineteenth century turned out to
be the time of unprecedented (and also never to be repeated) conversions of grass-
lands and forests to arable land. This trend is clear even for countries with limited
opportunities for farmland expansion: a steady increase in rice yields during Japan's
Tokugawa era (about 55% between 1600 and the 1860s) was far below the rate of
population growth, which itself experienced a nearly threefold rise, from 12 million
to 33 million people during the same period (Smil and Kobayashi 2012). Major
±
