Chemistry Reference
In-Depth Information
ecosystem changes in response to many change agents, including land use and
climate change. Forests can be either contributors or inhibitors of climate
change on regional scales, but they have the potential to play a significant role
in mitigating the pressures of global environmental change.
22
Land-use practices and climate change may work in concert to weaken the
ability of trees to defend themselves against pests, improve conditions for
native pests to flourish, and introduce unfamiliar pests to new locations. Non-
native forest pests have increased globally since the 1990s due to increased
international trade and other human activities
23
and now threaten forest
productivity and diversity.
24-27
For example, the root fungus Phytophthora
cinnamomi, which originated in Papua New Guinea and is now contributing to
forest mortality in the USA and Australia, and to Iberian oak decline in the
Mediterranean and coastal northwestern regions of Europe,
7
is a pathogen
requiring warm, wet soils to infect roots, and extreme weather conditions, such
as
d
n
1
r
2
n
g
|
8
drought
or
waterlogging,
can
increase
the
susceptibility
of
trees
to
infection.
7
In addition to non-native pest introduction, pollution is another human
cause of altered forest dynamics around the world. Forests adjacent to urban
and agricultural areas are responding to increased nitrogen deposition and
other airborne pollutants.
28,29
Human activities such as road-building and land
conversion lead to landscape fragmentation, which increases forest edges.
29
These edges can be ''hotspots'' of dry deposition, with as much as four times
the rate of atmospheric nutrient delivery as areas without edges.
30,31
The
difference between pollutant concentrations from the forest edge to the interior
can be very large, possibly even exponential, especially when particles are
transported horizontally by wind.
29
Several studies of excessive nitrogen
deposition have shown that the cumulative effects of nitrogen additions over
many
years
can
be
negative
due
to
a
phenomenon
called
''nitrogen
saturation'',
32
which can ultimately lead to nitrogen leaching into surface
waters.
33
3.1.1 Tropical Peat Swamp Forests
Montane peat swamps in cloud and other tropical forests play a significant
role in the global carbon cycle as they store a considerable amount of carbon in
their soils.
34,35
Approximately 60% of the known peatland forests are in south-
east Asia. Peat soils form from decayed woody plant debris decomposing in
high
precipitation
and
temperature
conditions
in
swamp
forests
at
low
elevations in river valleys.
36,37
A high estimate of the remaining historical peat swamp forests is 36%.
38
Drying of peat swamps through logging or for agricultural use is increasingly
common, but when these soils dry, they are extremely flammable.
39-41
Peat
soils are unique in their ability to burn above and below ground.
42
Clearance
and burning of peat swamp forest in south-east Asia could contribute to 3% of
total global human emissions.
43,44
The 1998 Indonesia fires burnt some 8
