The impact onecosystems 175these studies are indicative of the more serious levels of forest die-back
that are likely to occur with the rapid rate of climate change expected
with global warming (see box on page 173).These stresses on the world’s
forests due to climate change will be concurrent with other problems
associated with forests, in particular those of continuing tropical defor-
estation and of increasing demand for wood and wood products resulting
from rapidly increasing populations especially in developing countries.
If a stable climate is eventually re-established, given adequate time
(which could be centuries), different trees will be able to find again at
some location their particular climatic niche. It is during the period of
rapid change that most trees will find themselves unsatisfactorily located
from the climate point of view.
It was mentioned in Chapter 3 that forests represent a large store of
carbon; eighty per cent of above-ground and forty per cent of below-
ground terrestrial carbon is in forests. We also saw in Chapter 3 that
tropical deforestation due to human activities is probably releasing be-
tween 1 and 2 Gt of carbon into the atmosphere each year. If, because
of the rate ofclimate change, substantial stress and die-back occurs in
boreal and tropical forests (see box on page 173) a release of carbon will
occur. This positive feedback was mentioned in Chapter 3 (see the box
on page 40). Just how large this will be is uncertain but estimates as high
as 240 Gt over the twenty-first century for the above-ground component
alone have been quoted.^50
The above discussion has largely related to the impact of climate
change on natural forests where the likely impacts are largely negative.
Studies of the impacts on managed forests are more positive.^51 They sug-
gest that with appropriate adaptation and land and product management,
even without forestry projects that increase the capture and storage of
carbon (see Chapter 10), a small amount of climate change could in-
crease global timber supply and enhance existing market trends towards
rising market share in developing countries.
A further concern about natural ecosystems relates to the diversity of
species that they containand the loss of species and hence of biodiversity
due to the impact of climate change. Significant disruptions of ecosys-
tems from disturbances such as fire, drought, pest infestation, invasion of
species, storms and coral bleaching events are expected to increase. The
stresses caused by climate change, added to other stresses on ecological
systems (e.g. land conversion, land degradation, deforestation, harvest-
ing and pollution) threaten substantial damage to or complete loss of
some unique ecosystems, and the extinction of some endangered species.
Coral reefs and atolls, mangroves, boreal and tropical forests, polar and
alpine ecosystems, prairie wetlands and remnant native grasslands are
examples of systems threatened by climate change. In some cases the