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Phenology, the timing of seasonal activities of plants
and animals (such as breeding of birds and shooting and
flowering of plants), can be expected to be influenced by
climate change, as it is inmany cases temperature-depend-
ent. Evidence of phenological changes in numerous plant
and animal species as a consequence of climate change
is abundant and growing.
12
In general, spring activities
have occurred progressively earlier since the 1960s and
have been documented on all but one continent and in
all major oceans for all well-studied marine, freshwater
and terrestrial groups. Where insect life cycle events are
temperature-dependent, they may be expected to occur
earlier under increased temperatures; insects will pass
through their larval stages faster and become adults earlier.
All of these impacts on forest health will inevitably
have widespread impacts on the forest sector. Changes
in disturbance regimes and in the structure and function-
ing of naturally regenerated and planted forests will have
negative impacts on the productive functions of forest
ecosystems, which, in turn, will affect local economies.
Production patterns and trade in forestry commodities
will be altered as species are grown more competitively in
higher latitudes and altitudes. Conversely, markets may
be saturated due to increased mortality of trees following
disturbances, as has been experienced with the moun-
tain pine beetle outbreak in Canada. Decreased forest
ecosystem services, especially water cycle regulation,
soil protection and biodiversity conservation, may imply
increased social and environmental vulnerability.
By strengthening forest management practices, FAO
supports countries to achieve sustainable forest manage-
ment, including forest health protection. Effective forest
management helps ensure that forests remain healthy,
reducing the risk of forest degradation and increasing
resilience to climate change.
their ability to adapt; flexible species are less likely to be adversely
affected by climate change than specialist species.
4
The impact of a change in temperature on pests will vary depend-
ing on the climatic zone. In temperate regions, an increase in
temperature is likely to cause an increase in rates of insect survival
and could increase the risk of pest outbreaks. Warming in the
tropics, although proportionally smaller in magnitude, could nega-
tively affect the survival rate of insects and reduce the risk of pest
outbreaks. Compared to higher-latitude species, tropical insects
have very narrow ranges of climatic suitability and live very close to
their optimal temperature.
5
Climate plays a major role in defining the distribution limits of
insect species. With changes in climate, these limits are shifting as
species expand into higher latitudes and altitudes and disappear
from areas that have become climatically unsuitable.
6
Such shifts
are occurring in species whose distributions are limited by tempera-
ture, such as many temperate and northern species. It is now clear
that, during the 20th century, poleward and upward shifts of species
ranges occurred across many taxonomic groups and in a large diver-
sity of geographical locations.
7
The ability of a species to respond to global warming and expand
its range will depend on a number of life-history characteristics,
making the possible responses quite variable among species. Fast-
growing species will likely respond to warming by expanding
their distribution, whereas slow-growing species that need low
temperatures to induce diapause or dormancy, such as boreal and
mountain species in the Northern Hemisphere, will suffer range
contractions.
8
Range-restricted species, particularly polar and
montane species, show more severe range contractions than other
groups and are considered most at risk of extinction due to recent
climate change.
9
Range shifts may be limited by factors such as day
length or the presence of competitors, predators or parasitoids.
10
For example, the range expansion of insects that are host-specific
may be limited by the slower rate of spread of their host plant
species.
11
Forest fires are set to create pasture
Image: FAO
Many forest pests have altered their distribution and moved into
new areas in response to climate change
Image: François-Xavier Saintonge