which, if elevation is sufficiently high, transition to elfin
forests, páramo, or puna, depending on elevation and
exposure. The changes observed by Humboldt and his
associate, A. G. Bonpland, form the backbone of what
became the concept of plant associations or ecological
life zones. Humboldt clearly understood how changes
in physical conditions resulted in changes in ecosystem
characteristics.
Cloud Forests
Tropical cloud forests vary from one site to another,
but all share general characteristics. Here is a checklist
of what to look for as you ascend into these unique
ecosystems.
- Various species inhabit distinct elevation zones.
Species richness typically diminishes with elevation,
because conditions become harsher, but groups such
a ferns and orchids may exhibit higher diversities
than in lowland rain forests. - Moisture- seeking plants such as mosses and ferns
form abundant components of the vegetation
community. Tree ferns are particularly distinctive of
cloud forests. - Most species of plants and animals found in cloud
forests have strong taxonomic affinities with species
found in low- elevation rain forests, and some groups,
such as tanagers and hummingbirds, are better
represented in the mountains than in the lowlands
(plate 13- 4). - The stature of trees diminishes at high elevation,
sometimes resulting in dwarf trees. At Monteverde
Cloud Forest in Costa Rica, a place visited by many
ecotourists, canopy height varies from 20 to 40 m
(66– 131 ft) in sheltered sites but decreases to 5– 10
m (16.5– 33 ft), forming elfin forest, on exposed sites
such as ridges and peaks. - Sunlight is reduced due to the presence of fog,
a characteristic that also acts to reduce plant
productivity. - Precipitation is usually high. At Monteverde Cloud
Forest annual rainfall is between 250 and 350 cm
(98– 138 in), and dry season is characterized by mist
and cloud cover much of the day. Expect to get wet.
Certain other montane forests in parts of Central
America and those in the Chocó (along the western
coast of Colombia and Ecuador) experience higher
precipitation. Precipitation and mist keep these
forests moist, even during dry season.- The saturated air inhibits evapotranspiration, making
it more difficult for plants to obtain mineral nutrients
from soil, a factor that also limits plant productivity. In
other words, if the air is cool and highly saturated with
water, the physical conditions necessary for effective
uptake of water by plants are limited. - In addition to rainfall, precipitation occurs as fog-
drip, wherein water from fog condenses on leaf
and bark surfaces and drips on to the forest floor,
saturating the soil. At Monteverde Cloud Forest 22%
of the annual hydrologic input is due to wind- driven
water from fog. - Soil tends to become water- saturated and acidic,
creating bog- like conditions in some areas, where
decomposition is slowed by the high soil acidity. When
you walk in high- elevation areas the plant cover and
litter layer will feel spongy beneath your feet.
- The saturated air inhibits evapotranspiration, making
Neotropical Montane Forest
DistributionCloud forests are the dominant kind of ecosystem
along a narrow altitudinal belt, from 1,400 to 3,500 m
(4,590– 11,480 ft) along the eastern slope of the Andes.
Cloud forests occur in Venezuela, Colombia, Ecuador,
Peru, and Bolivia, and also in parts of southeastern
Brazil. Cloud forests also occur at higher elevations
in the Greater and Lesser Antilles, and in parts of
Nicaragua, Guatemala, Panama, and Costa Rica in
Central America. At Monteverde in Costa Rica, cloudPlate 13- 4. The widespread Bay- headed Tanager (Tangara
gyrola) frequents low- to mid- elevation cloud forests and
is often one of several tanager species traveling in mixed-
species foraging flocks. Photo by Jill Lapato.236 chapter 13 scaling the andes