NAG 301:
SOIL AND VEGETATION ECOLOGY
DR. K. CHATTERJEA
Lecture Topic: Tropical Rainforest Ecosystem
What are Tropical Rain Forests?
Tropical rain forests are the most complex ecosystems on earth.
Classification:
The rainforest is one of several types of forests found throughout the tropics, and
each type has different characteristics.
1.
The closed forests
a) Tropical moist forests
i)Tropical rain forests
ii) Tropical moist deciduous forests
b) Deciduous and semi-deciduous forests
2.
Open woodland
3.
Fallow forests
4.
Tropical forest plantations
a) Industrial plantations
b) Non-industrial plantations
Distribution:
Tropical rain forests provide a discontinuous belt of green vegetation around the
globe, between the Tropic of Cancer and Tropic of Capricorn --- particularly in
the hot, humid lower latitudes. Just under 1/2 of the tropical zone is covered by
forests (12 million km2).
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Climate and Rain forests
Climate exerts a strong influence: controls distribution as well as the patterns
and structures of vegetation and habitat.
1. Characteristic climate
Rain forests develop where every month is wet (100mm r.f.), short dry periods
lasting only a few days.
2. Seasonality
Most characteristic feature is the lack of pronounced seasonality. Uniform
climatic conditions mean that rain forest plants grow, flower and shed leaves all
year long, the rain forest animals reproduce and remain active throughout the
year.
There is no quiet time or rest period in the rain forest.
Age and stability
Rain forests are the world's oldest and most stable ecosystems. The distribution
today is largely historic: more restricted than in the past due to climatic changes.
Areas have also shrunk due to human activities (particularly since 1945). The
shrinkage in the area is also affecting the interior characteristics.
There is evidence that the rain forests in parts of Indonesia have existed for 60
million years.
Uniqueness: It is a highly regulated, tightly integrated
ecosystem,
in which everything: the smallest to the
largest of organism has its rightful place: NICHE. and
everything depends on every thing else: INTERACTION.
 It is the most abundant source of life.
 The complex ecosystem is finely adapted to a unique set of
climatic and environmental conditions.
 There is great density of plant materials.
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 The tropical rainforest has a very distinctive appearance and
structure, dominated by its vegetation.
 Rain forest trees: tall, with large leaves, straight trunk, high and
closed and closed canopy.
 Climbing plants: lianas, epiphytes.
 Roots and buttresses.
 Sunlight conditions.
 High competition.
 Vegetation is stratified.
 Animals and Food webs.
 Nutrient cycling.
 Rainforest soil: usually poor quality, with low mineral content,
deficient in nitrogen and phosphorus; generally well-drained ,
upper horizon enriched with organic matter, clay-rich -- as a rule
infertile: all nutrients tied to the vegetation.
The most important aspect is the species diversity:
100m2 of land of tropical rain forest can contain up to 230 different
tree species.
(a similar area in a temperate forest may contain only 7 - 10 species)
This is true for other living organisms: a recent study of Peruvian
rain forest revealed 41,000 different species of insects living in the
tree canopy within 100m 2, including 12,000 species of beetles.
Primary rain forest in Malaysia may contain up to 250,000 individual
plants per 100 m 2 forest land.
Why this diversity?????
Readings:
Edwards, David S. (1994) "A tropical rain forest": look through the book for the
topic areas covered.
Park, Chris (1994) "Tropical rainforest": Chapter 1
Whitmore, T.C. (1992) "An Introduction to Tropical rain forests": Chapters 1,
2, 3, 4, 5 -- selected sections.
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