Download Plant life of the Neotropical

Plant life of the Neotropical
Rainforest and Savanna
Ryan Goetz
Ann Calhoun
Ashley Dierenfeld
January 26, 2004
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“High species richness among many different taxons is one of the most distinctive
features of tropical forests worldwide and Neotropical lowland forests in particular” (Kricher,
1997, p.34). Upon first sight, the rainforest may appear as a vast world of green entangled
matter, but with further study it can be subdivided into four layers: the emergents, the canopy,
the understory, and the forest floor. Each level of the rainforest contains flora and fauna that
help to distinguish it from the other strata. Due to this plethora of diversity, the rainforest is
capable of housing millions of plant and animal species in a relatively small area.
The highest of the tropical rainforest layers is the emergent level. This layer consists of
trees that tower 250 feet or more above the forest floor with trunks measuring up to 16 feet in
circumference. “Most of these trees are broad-leaved, hardwood evergreens” (Rainforest
Layers). To support the massive emergents, the bases of these trees have developed support
systems called buttresses. A buttress may be described as “a root flaring out from the trunk to
form a flangelike base” (Kricher, 1997, p.24). These roots surround and radiate from a given
tree and may rise up to 30 feet before incorporating themselves into the main tree trunk. They
function to increase the surface area through which nutrients can be absorbed from the very poor
quality soil. Most importantly, buttresses help support against the strong winds encountered by
the tree’s crown high in the air. Along with buttresses, these high rising trees have made
additional adaptations. Due to their size, “emergents may take advantage of the greater air
movement above the canopy by developing winged seeds or fruits that are dispersed by wind to
other parts of the forest” (Rainforest Layers).
The canopy is the next stratum located below the emergent level. The canopy houses a
huge portion of the plant life found in the rainforest and has even been referred to as “the eighth
continent” (Newman, 2002, p.15). Trees here range from 60 to 150 feet in height, but are not the
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only plant species found in the canopy layer. “Canopy trees are crowned by the jewels of the
plant world, the epiphytes” (Newman, 2002, p.16). Epiphytes, also known as “air plants,”
include orchids, ferns, bromeliads, and cacti. In total, these epiphytes number up to 15,500
species in the Neotropical realm alone (Kricher, 1997). An epiphyte is defined as a plant which
grows on a host, but unlike parasitic plants epiphytes do not take nutrients away from the tree
(Mass and Westra, 1993). Instead, epiphytes gain nutrients from the air, falling rain, or compost
that lies on tree branches (Butler, 2004).
Due to the shortage of water, minerals, and nutrients in the canopy, rainforest plants have
developed a variety of adaptations. Canopy trees themselves have developed adaptations to
seasonal cues by only flowering and initiating seed germination early in the rainy season (Foster,
1996). Epiphytic plants have evolved to include structures that conserve water as well as unique
seed dispersal mechanisms. For example, epiphytic orchids produce far more seeds than their
ground counterparts to ensure the continuation of their species in subsequent generations.
Animals and insect interactions with these plants also play a large role in furthering the species.
“The dancing lady orchid of South America produces many tiny flowers that are positioned so
they “dance” even with the slightest breeze. These flowers are lively enough so that small
aggressive bees – thinking they are intruders – attack them and in the process, the bees are dusted
with pollen” (Butler, 2004). Orchids have also become highly adapted to the rainforest canopy
by developing roots with a large surface area for rapid absorption of nutrients and water.
“Bromeliads are abundant epiphytes in virtually all Neotropical moist forests” (Kricher,
1997, p.31). Belonging to the pineapple family, these plants form a vase or tank which holds
water and nutrients to sustain the plant during dry periods. These water reservoirs also serve as
microenvironments which house microorganisms, insects and a variety of animals such as frogs,
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snakes, lizards and even crabs. Cacti are another type of epiphyte found in the rainforest, but are
quite different from the cacti of more temperate and desert zones of the world (Butler, 2004).
These cacti grow in the canopy and lack sharp quills, but have developed elongated leaves for
light absorption.
“Vines are a distinct and important structural feature of rainforest, in a sense literally
tying the forest together” (Kricher, 1997, p.29). There are three distinct categories of vines
including lianas, bole climbers and stranglers. The lianas grow on trees and dangle from the
branches while bole climbers attach tightly to the tree trunk and ascend toward the canopy where
more sunlight can be absorbed. Stranglers begin growth at the top of a tree and descend to the
forest floor to establish their own root system. Once rooted, these plants may then eventually
choke their host tree.
The trees of the canopy, and all the additional plant life that coexists there, create an
umbrella that keeps light from penetrating through to the next layer of the rainforest—the
understory. Due to this umbrella effect only two to five percent of the sunlight from the canopy
filters through to the understory. “This limited light encourages the plant residents to devise
unique ways to survive, such as the solar-collecting dark green leaves” (Rainforest Layers).
Other unique survival mechanisms include the Hybanthus prunifoliu which is a shrub that
flowers in synchrony with the dry season. Whole clumps of these shrubs bloom at the same time
attracting its customary insect pollinator (Augspurger, 1996). Plants in the understory rarely
grow above 12 feet in height and include palms and ferns with lianas and vines also extending
through this region.
Traveling further down from the understory, you finally reach the lowest level of the
rainforest which is known as the forest floor. Very few plants grow here because this level
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receives zero to two percent of the sunlight from the canopy. The main function of the forest
floor is the decomposition of biomass that falls from areas above. “The floor itself is covered
with a litter of rapidly decomposing vegetation and organisms that break down into usable
nutrients” (Rainforest Layers). Because of the large concentration of humus on the forest floor,
many trees have shallow roots to quickly harvest and absorb the nutrients back into the
ecosystem.
Besides the vast areas of rainforest, the Neotropics are also made up of regions known as
savanna. “A savanna is a rolling grassland scattered with shrubs and isolated trees, which can be
found between a tropical rainforest and desert biome” (Savanna). Savannas typically experience
prolonged drought seasons. Annual rainfall in the savanna averages 39-79 inches per year with a
majority of rainfall occurring in a five to eight month period. This limited amount of rainfall
greatly affects the variety of plants and animals that inhabit the area.
“The growing season of the typical tropical savanna displays a short-to-tall, green-tosilvery shiny cover of bunch grasses, with either single trees or groups of trees widely scattered”
(Lieth, 2002). The drought season however, places a highly selective influence on plants which
must then adapt to these conditions in order to survive in the savanna. “Plants have adapted long
tap roots that can reach the deep water table, thick bark to resist annual fires, trunks that can store
water, and leaves that drop off during the winter to conserve water” (Savanna). Examples of
plant life in the savanna include members of the grass family (Gramineae) and members of the
tree family (Leguminosae).
Neotropical savannas occur on a wide variety of soil types and experience all extremes of
tropical climate. “Some savannas occur on wet water logged soils; others on dry sandy welldrained soils” (Kricher, 1997, p.234). Much like rainforest soils, savanna soils are nutrient poor
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and lack minerals such as phosphorus, calcium, magnesium, and potassium (Kircher, 1997). Do
to this poor quality soil, plant life is limited to the species that have adapted to the unique climate.
In extremely dry areas, fire plays a pivotal role in the renewal process of savanna plant
life. Most savannas probably experience mild fires frequently and major burns approximately
every two years (Kircher, 1997). “Fire protection gradually changes the density of woody plants
in numerous savannas around the world” (Moreira, 2000, p.9). If not driven out by fire, these
woody plants encroach and overtake native savanna species. Fires serve to maintain biodiversity
among the plants in the ecosystem by preventing competition.
Along with suppressed fire, humans have also imposed themselves as competition to the
savanna ecosystems. “Tropical savannas have been heavily impacted by human activity, with
large expanses transformed from a mixture of trees and grasses to open grassland and
agriculture” (Hoffmann and Jackson, 2000, p.1593). “Savanna regions are some of the most
highly populated places in the tropics, as well as the world, and it is certain that many will see a
substantial increase in human populations in the future” (Mistry, 2000, p.273).
The Neotropical rainforests are some of the last uncharted regions of the earth—holding
many unique and unknown species of plant and animal life. “More than half of the world’s
estimated 10 million species of plants, animals, and insects live in the tropical rainforests alone”
(Rainforest Facts). Plant species in this ecosystem are being threatened everyday due to the
deforestation of the rainforest in many parts of the globe. “Experts estimate that we are losing
137 plant, animal, and insect species every single day due to rainforest deforestation” (Rainforest
Facts). Continued study of the world’s Neotropical rainforests and savannas is prudent in order
to identify plant species before they vanish from the earth without ever being discovered.
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Literature Citied
Augspurger, C. (1996). A Cue for Synchronous Flowering. Smithsonian Institution.
Butler, R. (2004). Epiphytes. Retrieved January 24, 2004 from
http://www.mongabay.com/0405.htm
Foster, R. (1996). The Seasonal Rhythm of Fruit fall on Barro Colorado Island. Smithsonian
Institution.
Hoffmann, W. & Jackson, R. (2000). Vegetation—Climate Feedbacks in the Conversion of
Tropical Savanna to Grassland. Journal of Climate, 13 (9), 1593.
Kricher, J. (1997). A Neotropical Companion. (2nd ed.). Princeton: Princeton University Press.
Lieth, H. (2002). Savanna. Access Science @ McGraw-Hill. Retrieved January 24, 2004 from
http://www.accesscience.com/serverjava/Arknoid/science/AS/Encyclopedia/6/60/Est_603500_frameset.html
Longman, K.A. & Jenik, J. (1974). Tropical Forest and its Environment. (2nd ed.) New York:
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Mass, P.J.M., and Westra, L.Y.Th., (1993). Neotropical Plant Families. Germany/USA: Koeltz
Scientific Books.
Mistry, J. (2000). Savannas. Progress in Physical Geography, 24(2), 273.
Moffett, M. (1993). The High Frontier. Cambridge, Massachusetts: Harvard University Press.
Moreira, A. (2000). Effects of fire protection on savanna structure in Central Brazil. Journal of
Biogeography, 27(4), 9.
Newman, A. (1990) Tropical Rainforest. (Revised ed.) Hong Kong: Checkmark Books.
Rainforest Facts. (n.d.) Retrieved January 25, 2004 from http://www.rain-tree.com/facts.htm
Rainforest Layers. (n.d.) Retrieved January 24, 2004 from
http://www.pbs.org/tal/costa_rica/layers.html
Savanna. (n.d.) Retrieved January 24, 2004 from http://www.blueplanetbiomes.org/savanna.htm
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