Chemistry Reference
In-Depth Information
the El Ni ˜ o 1997-1998, forest mortality increased 50% post-drought
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as
canopy dieback increased radiant energy into the forest and increased the
temperature in the forest interior, further drying the soils and increasing fire
risk.
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In addition to climate change, human pressure on Amazonia is important.
Humans look to this region to exploit biofuels to substitute for oil, cattle and
swine industries, agro-industry expansion, sugar cane for ethanol, palm oil for
biodiesel and soy crops.
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Land-use changes increase habitat fragmentation,
edge effects of pollution and dry air circulation under forest canopy, and fire
ignition sources.
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3.1.3 Temperate Forests
In the USA, the regional importance of many tree species is changing rapidly.
Some tree species are experiencing dieback in response to precipitation and
temperature changes, while others are seeing shifts in species dominance. In a
regression tree analysis of eighty common trees species under five future
climate scenarios for 2100 counties in the eastern USA, Iverson and Prasad
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project that average species richness may remain the same or even increase
with climate change, but there are likely to be dramatic changes in forest type
in this region.
All five models
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predict an extirpation of spruce-fir forests in New England,
USA, and all but the two least-severe models show an extirpation of aspen and
birch species (both still largely reduced). Maple, beech and birch species are
largely reduced under all scenarios. The main increases are seen in oak-hickory
and oak-pine woodlands, which are projected to increase 34% and 290%,
respectively. The loblolly shortleaf pine is projected to decrease by 32% and
shift its range to the north and west. Longleaf slash pine is projected to
decrease by 31%, but elm-ash-cottonwood woodlands are projected to remain
in the upper Great Plains region of the USA.
According to their consensus models, 24 species in the eastern USA will see a
decline of at least 10%, while 35 species will see an increase in regional
importance, with 12 of these increasing by 100% or more. Recent national
forest assessments
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indicated that the total area of USA national forests has
been increasing annually, but that the amount of increase is slowing
dramatically. More recent US Forest Inventory Analysis (FIA) studies
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show
that some eastern states are levelling off in forest increase and others are
beginning to decline.
Coops and Waring
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used the 3-PG process-based model to predict forest
responses to climate change. Predictions of future tree distributions in the
Pacific Northwest of the USA show large changes in lodgepole pine and
ponderosa pine distributions. They show that lodgepole pine is most likely to
persist at sites with significant spring frost, summer temperatures below 15 uC,
and soils that are fully recharged from snow melt. Using future climate
projections, they predict a decrease of 8% in suitable lodgepole pine habitat
