Environmental Engineering Reference
In-Depth Information
resulted not only from CO
2
emissions from land-cover changes but also from the
release of CH
4
from l ooded soils and ruminant herds and N
2
O emissions from
manures. Ruddiman (2005) concluded that despite their relatively small numbers,
the i rst farmers eventually hijacked the entire global climate system, and that
humans have remained in control ever since. His hyperbolic statement (“in control”?)
focuses attention on the long history of the second-order effects of human actions
on the biosphere's productivity.
These effects have been magnii ed since the middle of the nineteenth century, i rst
with large-scale industrialization, energized by the combustion of coal, then with
the rapid post-1950 global economic growth, increasing dependence on hydrocar-
bons, a nearly universally high (Africa being the only exception) reliance on synthetic
nitrogenous fertilizers, increasing acreage devoted to paddy i elds, and expanded
dairy and beef production. Other anthropogenic emissions affecting primary pro-
ductivity include airborne pollutants (in the form of photochemical smog, black
carbon, and sulfur and nitrogen oxides) that can affect sensitive crops as well as
natural plant communities.
The accidental or deliberate introduction of pathogens can have devastating
effects on plant productivity, with some impacts extending to a large regional or
even continental scale. After its introduction on Asian nursery stock at the beginning
of the twentieth century, chestnut blight fungus (
Cryphonectria parasitica
) destroyed
the American chestnut, formerly a dominant species of the North American conti-
nent's eastern forests (Freinkel 2007). Another Asian pathogen, an ascomycete
fungus of
Ophiostoma
genus spread by bark beetles, has devastated i rst European
and then American elms (
Ulmus americana
). The European infestation began in
1910, the i rst affected trees were found in the United States in 1928, and by 1981
the slow westward spread of the fungus had reached Saskatchewan, leaving Alberta
and British Columbia as the only sizable unaffected areas (Hubbes 1999).
The latest dangerous accidental Asian invader is a small sap-sucking insect
(
Adelges tsugae
, woolly adelgid) that threatens the very survival of the two
eastern North American hemlock species,
Tsuga canadensis
and
Tsuga caroliniana
(Nuckolls et al. 2009). A reverse infestation is now afl icting Chinese forests as
Dendroctonus valens
, the red turpentine beetle native to North America, where it
colonizes dead and dying trees, is destroying millions of growing pines (Youngsteadt
2012).
Phytophthora ramorum
, an aggressive and unpredictably advancing fungus,
has caused sudden oak death in California and Oregon and since 2003 has been
destroying larch plantations in Britain (Brasier and Webber 2010).
