Chapter 21
Global Ecosystems
OVERVIEW
This chapter focuses on global patterns of vegetation.
-
Natural vegetation is the plant cover that would establish
itself in an area without human interference. Many areas of the
earth have been modified by humans but large areas of natural
vegetation still exist in more inaccessible areas.
- The life form of a plant refers to its physical structure,
size and shape. Lifeforms include trees, shrubs, lianas
and herbs.
-
Habitat refers to the conditions of slope, water drainage,
and soil type that influence the vegetation cover.
-
Water availability is one of the most important factors
influencing plant growth. Xerophytes are plants adapted to dry
conditions.
-
Temperature affects physiological processes in plants.
Plants have a temperature range within which they can survive
as well as optimum temperatures for each of their functions.
-
Ecological succession is a development sequence in
which plant communities succeed one another as they progress to
a stable climax, the most complex community of organisms possible
in an area.
- Succession starts with pioneer species that can survive
in harsh conditions. These pioneers moderate the harsh conditions
and gradually other species move in. Disturbances that
can interrupt the sequence include fires, insects, disease and
human activities such as cutting and clearing.
-
Biomes are the largest recognizable subdivision of
terrestrial ecosystems. These include the forest, savanna, grassland,
desert and tundra biomes.
- The Forest Biome includes six major types of forest:
- The low latitude rainforest is found in the equatorial
and tropical zone which experiences continuously warm temperatures
with consistent abundant rainfall. These ideal conditions produce
a forest of tall, closely set trees with a multilayered canopy
and the largest diversity of species of any lifezone.
- The monsoon forest grows in a wet-dry tropical climate.
The stress of the dry season results in a deciduous forest that
sheds its leaves. It has an open canopy allowing more development
in the lower forest layers.
- The subtropical evergreen forest is associated with
the moist subtropical climate. The native vegetation consists
of broadleaf and needleleaf evergreen trees although little natural
forest remains due to agricultural development.
- The midlatitude deciduous forest has a tall dense canopy
in summer but sheds its leaves in winter in response to the cold
temperatures.
- The needleleaf forest consists of a few species of
tall cone-shaped mostly evergreen coniferous trees. These trees
create a continuous deep shade at ground level which inhibits
the growth of shrubs and herbs. The needleleaf forest is associated
with the boreal forest climate and the high elevations of mountainous
areas.
- The schlerophyll forest develops in the Mediterranean
climate. The trees have adapted to the dry, hot summers by producing
small, hard, thick leaves that minimize water loss.
- The Savanna Biome is a product of the tropical wet-dry
climate. Vegetation changes from woodland to thorntree grassland
with increasing dryness. The adaptation to dryness includes deciduous
habit and small leaves or thorns.
- The Grassland Biome is found in the midlatitude and
subtropical zones which have well developed winter and summer
seasons. The biome includes both tall-grass prairie and steppe.
Steppe vegetation grows in the semi-arid subtype of the dry continental
climate.
- The desert biome includes both desert and semi-desert
subtypes. The area of semi-desert ranges from the tropical to
the midlatitude zone. The vegetation includes sparse xerophytic
shrubs and in some areas thorny trees and shrubs are adapted to
a long hot dry season with a short wet season. Desert vegetation
ranges from small hard leafed or spiny shrubs, succulent plants
and hard grasses to many areas with no vegetation covered by shifting
sands and salt flats.
- The tundra biome is found at high latitudes and high
elevations. Plants include low herbs, dwarf shrubs, sedges, grasses,
mosses and lichens. At high latitudes plant growth is influenced
by long winters with little light and short cool summers with
very long days. Permafrost underlies the surface and restricts
drainage and root development.
- As elevation increases, temperatures decrease and precipitation
increases leading to a sequence of vegetation zones or life zones
related to altitude.
-
Climate changes with latitude and longitude are reflected
in changes in vegetation. These changes are gradual not abrupt.
KEY TERMS
biomes forest biome monsoon forest
natural habitats subtropical evergreen
vegetation transpiration forest
life-form xerophytes midlatitude deciduous
perennial sclerophylls forest
lianas succession needleleaf forest
herbs climax sclerophyll forest
annuals pioneers savanna biome
forest formation classes grassland biome
woodland epiphytes desert biome
lichens low latitude tundra biome
plant ecology rainforest
STUDY QUESTIONS
- Differentiate between the major life forms that make up the
plant cover of the earth.
- Describe how the process of transpiration works.
- How does moisture availability affect plant growth?
- How does temperature affect plant growth?
- Describe the succession of plants from the pioneer stage to
the climax stage.
- Compare the low latitude rainforest with the needleleaf forest
of Pacific North America. How are these two forest types similar?
- How have humans impacted the forest biome?
- How does vegetation change as the climate becomes increasingly
dry?
- What are the types of vegetation associated with the Savanna
biome?
- How does the tall grass prairie differ from the steppe grassland?
- How does vegetation change in the transition from semi-desert
to dry desert?
- Describe how vegetation changes with elevation. What causes
this change?
Go to this chapter's quiz
Go to Chapter:
[Intro]
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[ Strahler Home Page ]
[ Preface ]
[ Geography Links ]
[ Wiley College Homepage ]
[ Talk to Wiley ]
[ Examination Copies ]
[ Wiley Geography Page ]