Environmental Engineering Reference
In-Depth Information
which poachers kill for their tusks. No effective solutions are at hand. The largest
ivory seizure since the 1989 trade ban, made in Singapore in 2002, contained 532
tusks with an average weight of more than 11 kg, substantially larger than the
usually traded tusks (Wasser et al. 2008). The scale of the ongoing illegal ivory
trade makes it clear that most African countries still cannot protect their elephants,
and periodic sales, often touted as “one-off” affairs, do not help improve that
dismal situation (Wasser et al. 2010). Loss of forest habitat and the killing of
anthropoid primates have reduced the distribution of gorillas and chimpanzees
to ever-smaller disconnected patches and brought their numbers to levels that
justify their inclusion in the critically endangered category for the mountain gorilla
(
Gorilla gorilla
and
G. beringei
) and to a somewhat less dire extent the Western
as well as endangered listing for both chimpanzee species,
Pan troglodytes
and
P. paniscus
(IUCN 2011).
For millennia, the greatest human impact on the biosphere was not caused by
actual harvests of food, feed, and wood but by the alteration and destruction of
ecosystems to create more open treed landscapes, expand agriculture and grazing,
and build terraces, settlements, and roads. We now know that such changes affected
even places that were seen until very recently as paragons of intact purity. The pre-
1492 Americas were not pristine wilderness but contained cultural landscapes,
including the i elds in the Great Lakes region, terracing and irrigation in Meso-
america, and settlements in the forests of Amazonia (Denevan 1992). Similarly, in
Central Africa van Gemerden et al. (2003) found that today's tree composition of
a species-rich rain forest still shows signs of historical disturbances most likely
caused by human use three to four centuries ago, a reality that makes the commonly
used categories of “old growth” and “secondary forest” less clear than is usually
assumed. This has an important implication for the identii cation of preindustrial
or preagricultural natural (intact, pristine) vegetation baselines.
Advancing deforestation and the conversion of grasslands and wetlands to agri-
cultural land or settlements led to declines in the biosphere's total net primary
production (NPP), but this loss was relatively much lower than the accompanying
loss of standing phytomass. Converting temperate or boreal forests to farmland
meant replacing ecosystems whose aboveground phytomass was mostly between
50 and 100 t C/ha with crop monocultures or low-diversity plant communities
whose peak (preharvest) phytomass typically remained well below 10 t/ha, an order
of magnitude loss, but the NPP of that old-growth forest was mostly between 5 and
8 t C/ha, compared to the 1-3 t C/ha of a low-yielding cereal crop. And replacing
an old-growth forest with fast-growing tree species grown for fuelwood may have
