Chapter 24
Global Ecosystems
OVERVIEW
This chapter focuses on global patterns of vegetation and the characteristics of the
vegetation found in the biomes of the Earth.
 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, herbs, and lichens.
 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 consistently 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. The monsoon forest 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. Adaptations to dryness
include 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 semidesert 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.
KEY TERMS
biomes
natural vegetation
life-form
perennial
lianas
herbs
annuals
forest
woodland
lichens
forest biome
low latitude rainforest
monsoon forest
subtropical evergreen
midlatitude deciduous
needleleaf forest
sclerophyll forest
savanna biome
grassland biome
desert biome
tundra biome
STUDY QUESTIONS
1. Differentiate between the major life forms that make up the plant cover of the Earth.
2. Compare the low latitude rainforest with the needleleaf forest of Pacific North
America. How are these two forest types similar?
3. How have humans impacted the forest biome?
4. How does vegetation change as the climate becomes increasingly dry?
5. What are the types of vegetation associated with the Savanna biome?
6. How does the tall grass prairie differ from the steppe grassland?
7. How does vegetation change in the transition from semi-desert to dry desert?
8. Describe how vegetation changes with elevation. What causes this change?
CHAPTER QUIZ
Multiple Choice Questions
1. Trees that shed their leaves seasonally are classed as:
a) deciduous
b) evergreen
c) xerophytes
d) sclerophyll
2. The largest diversity of species of any lifezone is found in the:
a) needleleaf forest
b) monsoon forest
c) subtropical evergreen forest
d) low latitude rainforest
3. Which of the following lifezones has been most impacted by human land use?
a) low latitude rainforest
b) tundra
c) needleleaf forest
d) subtropical evergreen forest
4. Which of the following biomes is most closely associated with a moist environment?
a) forest
b) grasslands
c) savanna
d) tundra
5. The tree crowns of the ____________ tend to form two or three layers.
a) low latitude rain forest
b) monsoon forest
c) montane forest
d) subtropical evergreen forest
True/False Questions
1.
2.
3.
4.
The tall grass prairie is almost entirely in its natural state. (T/F)
Fire is an important influence in the savanna biome. (T/F)
The boundaries of vegetation zones are usually abrupt. (T/F)
A plant that attaches itself to the trunk, branches, or foliage of a tree or liana is an
epiphyte. (T/F)
Short Answer Questions
1. How has the sclerophyll forest adapted to the stress of the Mediterranean climate?
2. Why do the midlatitudes contain most of the human influenced vegetation?
3. Why is tundra vegetation found both at high elevations and at high latitudes?
Short Essay Questions (1 - 2 paragraphs)
1. Describe how forests change as you move from the warmer equatorial to the colder
polar regions.
2. Describe how the change in vegetation that occurs with increasing elevation is similar
to the change in vegetation that occurs with increasing latitude.
Internet Resources
1. Biomes of the world:
<http://www.snowcrest.net/geography/slides/biomes/index.html>
2. Biome basics: <http://www.richmond.edu/~ed344/webunits/biomes/biomes.html>
3. Global land environments since the last interglacial:
<http://www.esd.ornl.gov/projects/qen/nerc.html>
4. Actual and potential global vegetation cover: <http://www.tkl.iis.utokyo.ac.jp/RGOE/actual.html>
5. Global vegetation monitoring: <http://www.gvm.sai.jrc.it/>
6. Spatial interpolation of categorical data – an application for mapping global
vegetation data: <http://darkwing.uoregon.edu/~jholman/thesis.html>
7. The Boreal Forest – a global ecosystem:
<http://atlas.gc.ca/english/facts/borealforest/boreal_global_e.html>