Environmental Engineering Reference
In-Depth Information
one or more of the above factors (Sanderson et al. 2002). Tundra and boreal forests
had the lowest inl uence scores, and tropical and subtropical grasslands, mangroves,
and temperate forests were the most affected biomes.
The most recent study of this kind mapped the world's intact forest landscapes,
dei ned as area of at least 500 km
2
or 50,000 ha devoid of any signs of signii cant
human activity (Potapov et al. 2008). The global extent of such landscapes was just
over 13 Mkm
2
, or slightly less than a quarter (23.5%) of all forests, with nearly
90% of the total roughly split between dense tropical and subtropical forests and
the boreal biome. Large intact forest areas were found in 66 of 149 countries having
forest biomes, but just three of them, Canada, Russia, and Brazil, accounted for
nearly two-thirds. Unfortunately, less than 10% of the remaining intact forests were
strictly protected, and less than a i fth had any form of protection.
And the real extent of intact forests may be substantially greater. Potapov et al.
(2008) assumed that all i res near the vicinity of human settlements were set by
people, and this rule led them to classify more than 400,000 km
2
of Canadian forests
as “not intact.” But Lee (2009) pointed out that such a rule, perhaps valid for Siberia,
is inappropriate for Canadian forests, where i re, whether close to or far from any
settlement, is an expected natural agent of change. If a simple assumption change
can “reclaim” nearly half a million square kilometers of wilderness, what other rules
in that study of forest intactness, and in other similar mappings, may result in less
dramatic human impacts? All of these realities force us to conclude that while hybrid
ecosystems are ubiquitous, the complexities of such landscapes raise challenging
questions about the “naturalness” of our environment and about authenticity in
nature (Dudley 2011).
As for those audacious claims that humans are now supreme and natural systems
are somehow subserviently embedded within human systems, their authors would
do well to remember that the fundamental geophysical variables that make the
biosphere possible, that make the Earth habitable, that are the primary governors
of climate, that subject it to Milankovi´ cycles, and that are the pacemakers of the
ice ages (ranging from the Sun's electromagnetic l ux and the planet's tilt, orbital
distance, path and its eccentricity to the Earth's shape and rotation speed) are
abso-
lutely beyond
any human inl uences (Milankovitch 1941; Hays, Imbrie, and Shack-
leton 1976). Not surprisingly, Claussen et al. (2005) found no support for Ruddiman's
(2005) claim that the early Holocene anthropogenic CO
2
and CH
4
emissions pre-
vented a glaciation that should have taken place 4,000-5,000 years ago.
Nor can there be ever any human control of the fundamental planet-forming
processes of plate tectonics that govern climate by redistributing land masses
