14.2.1.4. Temperate Forests and Mountain and Polar Ecosystems
Studies carried out in Latin America on the potential impact of climate change
in mountain ecosystems report an increase in mean temperature followed by a
gradual reduction of glaciers in the high mountains (Flórez, 1992). As
Flórez (1992) has reported, in Colombia there will be an ascent of the
altitudinal limits of forest and agriculture, reducing the paramo life zone
and possibly causing disappearance of current flora and fauna. The limits of
the Andean and sub-Andean life zones also would ascend, as would the upper limit
of the lowland tropical forest zone (Pabón, 1995b; van der Hammen, 1997).
In the same way, studies in Costa Rica suggest the same effect on the tropical
montane cloud forests, where biodiversity is very high. Halpin and Smith (1991)
identify three types of changes in the areal arrangement of ecoclimatic zones
in Costa Rica from four GCM models (UKMO, GISS, OSU, and GFDL). The first change
is a strong trend toward displacement of montane and subalpine zones by warmer
pre-montane climate types. The second change indicates potential heat stress
in vegetation, and the third is a change in all altitudinal levels toward warmer
climate types.
Villers-Ruiz and Trejo-Vázquez (1997) determined the vulnerability of
Mexican forest ecosystems and forestry areas to climate change under two climate
change scenarios, considering doubled-CO2 concentrations (CCCM and GFDL-R30
models). They used Holdridge's life zones classification for their analysis.
Their results showed that the most affected life zones would be temperate cold
and warm forests. They conclude that increases in temperature and decreases
in precipitation would reduce the extent of cool temperate and warm temperate
life zones but would increase dry and very dry tropical forest zones.
The most affected natural protected areas in Mexico would be those located
in the northern and western regions of the country (Villers-Ruiz and Trejo-Vázquez,
1998). Similarly, the most affected forest exploitation areas would be those
located in the western part of Mexico. These changes suggest that life zones
that sustain temperate desert, warm temperate desert, and cool temperate wet
forest would disappear or would be severely reduced (Villers-Ruiz and Trejo-Vázquez,
1998). These changes would put national cellulose and paper production at risk
because high and medium forestry production areas are located in the northern
and western states of Mexico (Vargas-Pérez and Terrazas-Domínguez,
1991). Cool, temperate moist and wet forests (coniferous and oak forests) currently
occupy these zones.
Natural protected areas would be affected by the change of their original vegetation,
causing a reduction of animal populations. Sierra de Manantlán and the
Monarch Butterfly reserves are examples of climate change impacts on natural
protected areas (Villers-Ruiz and Trejo-Vázquez, 1998).
The severe drought during early 1998, associated with an El Niño event,
resulted in an unusually large number of forest fires and severe economic losses
(Palacio et al., 1999). Cairns et al. (2000) estimates fuel consumption
and coal emission in tropical Mexico for those events. The land-use/land-cover
classes most extensively impacted were evergreen tropical forests and fragmented
forests. They point out that similar fire events may be expected more frequently
in the future if global change shifts toward a warmer and drier climate. The
atmospheric consequences of those events were continuous emission of smoke to
the United States for a large period of time (Wright, 1999). The costs from
droughts and forest fires in Mexico and Central America during El Niño
were approximately US$600 million.
The effects of a strong El Niño event on terrestrial ecosystems of Peru
and Ecuador are as relevant (with high possibility) as in the ocean and shores
(Arntz and Fahrbach, 1996). Increases in precipitation were recorded in Ecuador,
Colombia, and northern Peru during the 1982-1983 El Niño event,
with a simultaneous decrease in rainfall southward. Increases in precipitation
also were recorded during the 1941 El Niño event. However, the increase
in rainfall should not be assumed to be homogeneous. Whereas significant increases
have been recorded in northern Peru, Ecuador, and even Colombia, severe droughts
occurred around the Titicaca region and in northern Chile. In the highlands
of the Andes as well, a north-south gradient in rainfall has been observed during
El Niño events.
Increases in precipitation during El Niño events result in enhanced
vegetation cover (from 5 to 89%) and primary productivity (from 0.005 to 3.5
t yr-1) in coastal desert ecosystems. In northern Peru, strong El Niño
events increase not only the ephemeral vegetation but also seed germination
and seedling recruitment of woody species. Increases in precipitation from 20
mm (1996) to more than 1,000 mm (December 1997 to May 1998) have been recorded
in Belizario in northern Peru. This increase in rainfall was correlated with
a significant increase in annual NPP of the herb layer in a dry Prosopis pallida
woodland, from almost zero in December 1997 to 0.51 g-2 yr-1 in February 1998.
In the same region, the annual NPP of the shrub and tree layers also were significantly
higher during the El Niño event, but fruit productivity decreased as
a result of the mechanic effect of rain drops on buds, flowers, and immature
fruits. Demographic explosions of two land snails were observed (Torres Guevara,
1992) during the increase in vegetation cover and annual NPP in northern Peru
during 1998.
Besides the foregoing observations, little information has been reported about
the explosive development of plant cover during strong El Niño events.
Moreover, no data are available about the way in which this enhanced annual
NPP impacts wildlife and range activities. According to Arntz and Fahrbach (1996),
however, during this vegetation "explosion," insects, snails, and
other invertebrates increase in number and diversity. Consequently, vertebrates
such as rodents, birds, and foxes benefit from a diversified and enriched diet.
Observational studies confirm a significant increase in the density of rodents
(Muridae and Cricetidae), followed by an increase in the activity of foxes (Dusicyon
culpaeus). The considerable increase in the density of insects and rodent
populations has a direct impact on agriculture. Damage associated with the incidence
of pests on crops is further aggravated by the occurrence of floods.
Extraordinarily strong precipitation during El Niño events is not restricted
to the continent. The Galápagos Islands also were affected by increased
rainfall during 1983. As in continental ecosystems, enhanced annual NPP had
direct consequences on the densities of species in higher trophic levels (Tarazona
and Valle, 1999).
As a consequence of the unusual combination of climatic and meteorological
conditions attributed to the El Niño before and after the winter of 1997-1998,
fires had a particularly strong effect on forests in Mexico. The number of fires
was twice the average for the period 1992-1997 and 35% higher than the
historical high mark recorded in 1988. The area affected was three times larger
than the average for the same period (Barkin and García, 1999). Economic
losses from those fires were estimated to be about US$230 million (Delgadillo
et al., 1999). Following the increase in rainfall associated with the
strong El Niño event in 1982-1983, the next 2 years were exceptionally
dry and cold in the Galápagos. Most of the plant biomass produced during
the rainy years died back and accumulated as a result of the low decomposition
rate. This increase in dry biomass is directly associated with the occurrence
of fires affecting large areas. Recovery of plant cover after fires has been
different in grasslands and woody vegetation. Whereas species diversity in grasslands
has increased, fires had dramatic effects on woody vegetation because many trees
and shrubs were severely affected by underground fires (Arntz and Fahrbach,
1996).
Scenarios of climate change for Latin America mountain areas are highly uncertain
because available GCMs do not provide sufficiently accurate local predictions.
Glacial retreat is underway in various parts of the Andes and in the ice fields
at the southern tip of the continent (Canziani et al., 1998). Shifting
of ecosystems upslope is expected to result in loss of some vegetation types
and increased vulnerability to genetic and environmental pressures.
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