Terrestrial ecosystems

1. Terrestrial Ecosystems
Rounak Choudhary
M.Sc. (Gold Medalist), UGC-NET & ICAR-ASRB NET Environmental Science, DCB Ornithology, PGD Industrial Safety, Health and Environment

2. Our introduction of aquatic environments was dominated by discussion of
the physical and chemical properties of water—characteristics such as
depth, flow rate, and salinity
• When considering the term terrestrial environment ,
however, people typically do not think of the physical and
chemical characteristics of a place. What we most likely
visualize is the vegetation: the tall, dense forests of the wet
tropics; the changing colors of autumn in a temperate forest;
or the broad expanses of grass that characterize the prairies.
• Animal life depends on the vegetation within a region to
provide the essential resources of food and cover—and as
such, the structure and composition of plant life constrain the
distribution and abundance of animal life. But ultimately, as
with aquatic environments, the physical and chemical
features of terrestrial environments set the constraints for
life.

3. Soil Is the Foundation upon Which All
Terrestrial Life Depends
• Soil is the medium for plant
growth.
• nature’s recycling system,
which breaks down the
waste products of plants and
animals and transforms them
into their basic elements;
and habitat to a diversity of
animal life, from small
mammals to countless forms
of microbial life.

5. Profiles and
general
description of
the 12 major
soil orders of
the world

7. BIOMES
• In 1939, ecologists F. E. Clements and V. E. Shelford
introduced an approach for combining the broad-scale
distribution of plants and associated animals into a single
classification system. Clements and Shelford called these
biotic units biomes.
• Biomes are classified according to the predominant plant
types.
• Depending on how finely biomes are classified, there are at
least eight major terrestrial biome types.
• Tropical forest, Temperate forest, Conifer forest (taiga or
boreal forest), Tropical savanna, Temperate grasslands,
Chaparral (shrublands), Tundra, and Desert

8. • These broad categories reflect the relative contribution of
three general plant life-forms: trees, shrubs, and grasses.
• A closed canopy of trees characterizes forest ecosystems.
Woodland and savanna ecosystems are characterized by the
codominance of grasses and trees (or shrubs). As the names
imply, shrubs are the dominant plant form in shrublands, and
grasses dominate in grasslands. Desert is a general category
used to describe the scarcity of plant cover.

10. • When the plant
ecologist Robert
Whittaker of Cornell
University plotted
these biome types
on gradients of
mean annual
temperature and
mean annual
precipitation, he
found they formed a
distinctive climatic
pattern, as graphed

11. • Within the broad classes of forest and woodland ecosystems in which
trees are dominant or codominant, leaf form is another plant
characteristic that ecologists use to classify ecosystems.
• Leaves can be classified into two broad categories based on their
longevity. Leaves that live for only a single year or growing season are
classified as deciduous, whereas those that live beyond a year are called
evergreen.
• Ecosystems characteristic of warm, wet climates with no distinct
seasonality are dominated by broadleaf evergreen trees and are called
tropical (and subtropical) rain forest. As conditions become drier, with a
distinct dry season, the broadleaf evergreen habit gives way to
droughtdeciduous trees that characterize the seasonal tropical forests.
• As precipitation declines further, the stature and density of these trees
declines, giving rise to the woodlands and savannas that are
characterized by the coexistence of trees (shrubs) and grasses.
• As precipitation further declines, trees can no longer be supported,
giving rise to the arid shrublands (thorn scrub) and desert.

13. Forests
Tropical Temperate Boreal
•Open Canopy Boreal
•Closed Canopy Boreal
•Deciduous Forest
•Temperate Rainforest
•Evergreen Rainforest
•Tropical Moist Forest
•Tropical Dry Forest
•Mangrove

15. Tropical Forests Characterize the
Equatorial Zone
• Tropical rainforests are
mainly located between
the latitudes of 23.5°N (the
Tropic of Cancer) and 23.5°S
(the Tropic of Capricorn)—
the tropics. Tropical
rainforests are found in
Central and South America,
western and central Africa,
western India, Southeast
Asia, the island of New
Guinea, and Australia where
the temperatures are warm
throughout the year and
rainfall occurs almost daily.

16. • The largest and most continuous region of rain forest in the
world is in the Amazon basin of South America.
• The second largest is located in Southeast Asia, and the third
largest is in West Africa around the Gulf of Guinea and in the
Congo basin.
• Smaller rain forests occur along the northeastern coast of
Australia, the windward side of the Hawaiian Islands, the
South Pacific Islands, the east coast of Madagascar, northern
South America, and southern Central America.
• Tropical rain forests have a high diversity of plant and animal
life. Covering only 6 percent of the land surface, tropical rain
forests account for more than 50 percent of all known plant
and animal species.
• Nearly 90 percent of all nonhuman primate species live in the
tropical rain forests of the world

17. • Tropical rain forests may be divided into five vertical layers: emergent
trees, upper canopy, lower canopy, shrub understory, and a ground layer
of herbs and ferns.

19. Temperate Rainforests
• Temperate rainforests are located in the mid-latitudes, where
temperatures are much more mild than the tropics.
Temperate rainforests are found mostly in coastal,
mountainous areas. These geographic conditions help create
areas of high rainfall. Temperate rainforests can be found on
the coasts of the Pacific Northwest in North America, Chile,
the United Kingdom, Norway, Japan, New Zealand, and
southern Australia.

20. • As their name implies, temperate rainforests are much cooler
than their tropical cousins, averaging between 10° and 21°C
(50° and 70°F). They are also much less sunny and rainy,
receiving anywhere between 150-500 centimeters (60-200
inches) of rain per year. Rainfall in these forests is produced
by warm, moist air coming in from the coast and being
trapped by nearby mountains.
• Temperate rainforests are not as biologically diverse as
tropical rainforests. They are, however, home to an incredible
amount of biological productivity, storing up to 500-2000
metric tons of leaves, wood, and other organic matter per
hectare (202-809 metric tons per acre).
• Cooler temperatures and a more stable climate slow down
decomposition, allowing more material to accumulate.
• This productivity allows many plant species to grow for
incredibly long periods of time. Temperate rainforest trees
such as the coast redwood in the U.S. state of California and
the alerce in Chile are among the oldest and largest tree
species in the world.

21. • Bobcats (Lynx rufus), mountain lions (Puma concolor), and
black bears (Ursus americanus) are major predators in the
rainforests of the Pacific Northwest. In Australia, ground
dwellers such as wallabies, bandicoots, and potoroos feast on
the foods provided by the forest floor. Chile’s rainforests are
home to a number of unique birds such as the Magellanic
woodpecker and the Juan Fernández firecrown, a
hummingbird species that has a crown of color-changing
feathers.

23. Tropical seasonal forests have yearly dry
seasons
• Many tropical regions are characterized by distinct wet and
dry seasons, although temperatures remain hot year-round.
These areas support tropical seasonal forests : drought-
tolerant forests that look brown and dormant in the dry
season but burst into vivid green during rainy months.
• These forests are often called dry tropical forests because
they are dry much of the year; however, there must be some
periodic rain to support tree growth. Many of the trees and
shrubs in a seasonal forest are drought-deciduous: They lose
their leaves and cease growing when no water is available.
Seasonal forests are often open woodlands that grade into
savannas.

26. Temperate Forests
• The average daily temperatures range between -30°C
and 30°C with a yearly average of 10°C (50°F). Hot
summers and cold winters are typical in this biome.

27. • During the fall, trees change color and then lose their
leaves. This is in preparation for the winter season.
Because it gets so cold, the trees have adapted to the
winter by going into a period of dormancy or sleep. They
also have thick bark to protect them from the cold
weather. Trees flower and grow during the spring and
summer growing season.
• Many different kinds of trees, shrubs, and herbs grow in
deciduous forests. Most of the trees are broadleaf trees
such as oak, maple, beech, hickory and chestnut. There
are also several different kinds of plants like mountain
laurel, azaleas and mosses that live on the shady forest
floor where only small amounts of sunlight get through.

29. Conifer Forests Dominate the Cool
Temperate and Boreal Zones
• Conifer forests, dominated by needle-leaf evergreen trees,
are found primarily in a broad circumpolar belt across the
Northern Hemisphere and on mountain ranges, where low
temperatures limit the growing season to a few months each
year.

31. • The largest expanse of conifer forest, in fact the largest
vegetation formation on Earth, is the boreal forest, or taiga
(Russian for “land of little sticks”).
• This belt of coniferous forest, encompassing the high latitudes
of the Northern Hemisphere, covers about 11 percent of
Earth’s terrestrial surface.
• Three major vegetation zones make up the taiga:
(1) the forest–tundra ecotone with open stands of stunted
spruce, lichens, and moss;
(2) the open lichen woodland with stands of lichens and black
spruce; and
(3) the main boreal forest

33. Tropical Savannas Are Characteristic of
Semiarid Regions with Seasonal Rainfall
• The term savanna was originally used to describe the treeless
areas of South America.
• Now it is generally applied to a range of vegetation types in
the drier tropics and subtropics characterized by a ground
cover of grasses with scattered shrubs or trees.
• Savanna includes an array of vegetation types representing a
continuum of increasing cover of woody vegetation, from
open grassland to widely spaced shrubs or trees and to
woodland.
• Savannas are associated with a warm continental climate with
distinct seasonality in precipitation and a large interannual
(year to year) variation in total precipitation

35. • Savannas, despite their differences in vegetation, exhibit a
certain set of characteristics. Savannas occur on land surfaces
of little relief—often on old plateaus, interrupted by
escarpments and dissected by rivers.
• Continuous weathering in these regions has produced
nutrient-poor Oxisols, which are particularly deficient in
phosphorus.
• Alfisols are common in the drier savannas, whereas Entisols
are associated with the driest savannas.
• Subject to recurrent fi res, the dominant vegetation is fire
adapted. Grass cover with or without woody vegetation is
always present.
• Savannas are characterized by a two-layer vertical structure
due to the ground cover of grasses and the presence of
shrubs or trees.

36. • The yearly cycle of plant activity and subsequent productivity in
tropical savannas is largely controlled by the markedly seasonal
precipitation and corresponding changes in available soil moisture.
Most leaf litter is decomposed during the wet season, and most
woody debris is consumed by termites during the dry season.
• Savannas can support a large and varied assemblage of
herbivores—invertebrate and vertebrate, grazing and browsing. The
African savanna, visually at least, is dominated by a large and
diverse ungulate fauna of at least 60 species that share the
vegetative resources. Some species, such as the wildebeest and
zebra, are migratory during the dry season.
• Savanna vegetation supports an incredible number of insects: fl ies,
grasshoppers, locusts, crickets, carabid beetles, ants, and detritus-
feeding dung beetles and termites. Mound-building termites
excavate and move tons of soil, mixing mineral soil with organic
matter. Some species construct extensive subterranean galleries
and others accumulate organic matter.
• Living on the ungulate fauna is an array of carnivores including the
lion, leopard, cheetah, hyena, and wild dog. Scavengers, including
vultures and jackals, subsist on leftover prey.

38. Grassland Ecosystems of the Temperate
Zone Vary with Climate and Geography
• Natural grasslands occupy regions where rainfall is between
25 and 80 cm a year, but they are not exclusively climatic.
• Many exist through the intervention of fire and human
activity. Conversions of forests into agricultural lands and the
planting of hay and pasturelands extended grasslands into
once forested regions. Formerly covering about 42 percent of
the land surface of Earth, natural grasslands have shrunk to
less than 12 percent of their original size because of
conversion to cropland and grazing lands.
• Grasslands do the poorest where precipitation is lowest and
the temperatures are high. They are tallest in stature and the
most productive where mean annual precipitation is greater
than 800 mm and mean annual temperature is above 15°C.

41. • Grasslands support a diversity of animal life
dominated by herbivorous species, both invertebrate
and vertebrate. Large grazing ungulates and burrowing
mammals are the most conspicuous vertebrates.
• The African grassveld once supported great migratory
herds of wildebeest ( Connochaetes taurinus ) and
zebra ( Equus spp.) along with their associated
carnivores, the lion ( Panthera leo ), leopard ( Panthera
pardus ), and hyena ( Crocuta crocuta ). The great
ungulate herds have been destroyed and replaced
with sheep, cattle, and horses.
• The Australian marsupial mammals evolved many
forms that are the ecological equivalents of placental
grassland mammals. The dominant grazing animals are
several kangaroo species, especially the red kangaroo (
Macropus rufus ) and the gray kangaroo ( Macropus
giganteus ).

42. Deserts Represent a Diverse Group of
Ecosystems
• The arid regions of the world occupy from 25 to 35 percent of
Earth’s landmass.
• Most of the arid environments are found in the Northern
Hemisphere. The Sahara, the world’s largest desert, covers
approximately 9 million km 2 of North Africa. It extends the
breadth of the African continent to the deserts of the Arabian
Peninsula, continuing eastward to Afghanistan and Pakistan
and finally terminating in the Thar Desert of northwest India.
The temperate deserts of Central Asia lie to the north. The
most westerly of these is the Kara Kum desert region of
Turkmenistan. Eastward lie the high-elevation deserts of
western China and the high plateau of the Gobi Desert.

44. • The deserts of southern Africa include three regions. The
Namib Desert occupies a narrow strip of land that runs along
the west coast of Africa from southern Angola to the border
of the cape region of South Africa. This region continues
south and east across South Africa as the Karoo, which
merges with the Kalahari Desert to the north in Botswana.
The most extensive region of arid land in the Southern
Hemisphere is found in Australia, where more than 40
percent of the land is classified as desert.
• Deserts are not the same everywhere. Differences in
moisture, temperature, soil drainage, topography, alkalinity,
and salinity create variations in vegetation cover, dominant
plants, and groups of associated species. There are hot
deserts and cold deserts, extreme deserts and semideserts,
ones with enough moisture to verge on being grasslands or
shrublands, and gradations between those extremes within
continental deserts.

45. • Two examples of hot deserts.
• (a) The Chihuahuan Desert in Nuevo
Leon, Mexico. The substrate of this desert
is sand-sized particles of gypsum.
• (b) Dunes in the Saudi Arabian desert
near Riyadh. Note the extreme
sparseness of vegetation.

46. • Cool deserts—including the Great Basin of North America,
the Gobi, Takla Makan, and Turkestan deserts of Asia—and
high elevations of hot deserts are dominated by Artemisia
and chenopod shrubs

47. • Both plants and animals adapt to the scarcity of water by either
drought evasion or drought resistance. Drought-evading plants
flower only when moisture is present. They persist as seeds during
drought periods, ready to sprout, flower, and produce seeds when
moisture and temperature are favorable. If no rains come, these
ephemeral species do not germinate and grow.
• Despite their aridity, desert ecosystems support a surprising
diversity of animal life, including a wide assortment of beetles, ants,
locusts, lizards, snakes, birds, and mammals. The mammals are
mostly herbivorous species. Grazing herbivores of the desert tend
to be generalists and opportunists in their mode of feeding. They
consume a wide range of species, plant types, and parts. Desert
rodents, particularly the family Heteromyidae, and ants feed largely
on seeds and are important in the dynamics of desert ecosystems.
Seed-eating herbivores can eat up to 90 percent of the available
seeds. That consumption can distinctly affect plant composition and
plant populations. Desert carnivores, such as foxes and coyotes,
have mixed diets that include leaves and fruits; even insectivorous
birds and rodents eat some plant material. Omnivory, rather than
carnivory and complex food webs, seems to be the rule in desert
ecosystems.

48. Mediterranean Climates Support
Temperate Shrublands
• Shrublands—plant communities where the shrub growth
form is either dominant or codominant—are difficult types of
ecosystems to categorize, largely because of the difficulty in
characterizing the term shrub itself
• In general, a shrub is a plant with multiple woody, persistent
stems but no central trunk and a height from 4.5 to 8 m.
• The shrub growth form can be a dominant component of a
variety of tropical and temperate ecosystems, including the
tropical savannas and scrub desert communities.

50. • All five regions support similar-looking communities of xeric
broadleaf evergreen shrubs and dwarf trees known as
sclerophyllous ( scleros, “hard”; phyll, “leaf”) vegetation with
a herbaceous understory.
• Sclerophyllous vegetation possesses small leaves, thickened
cuticles, glandular hairs, and sunken stomata, all
characteristics that function to reduce water loss during the
hot, dry summer period.

52. Low Precipitation and Cold Temperatures
Define the Arctic Tundra
• Encircling the top of the Northern Hemisphere is a frozen
plain; dotted with lakes; and crossed by streams. Called
tundra, its name comes from the Finnish tunturi, meaning “a
treeless plain.”
• The arctic tundra falls into two broad types: tundra with up to
100 percent plant cover and wet to moist soil and polar
desert with less than 5 percent plant cover and dry soil.

55. • Conditions unique to the Arctic tundra are a product of at
least three interacting forces:
• (1) the permanently frozen deep layer of permafrost;
• (2) the overlying active layer of organic matter and mineral
soil that thaws each summer and freezes the following
winter; and
• (3) vegetation that reduces warming and retards thawing in
summer.
Permafrost chills the soil, retarding the general growth of plant
parts both above- and belowground, limiting the activity of soil
microorganisms, and diminishing the aeration and nutrient
content of the soil.

56. • Dominant vertebrates on the Arctic tundra are herbivores,
including lemmings, Arctic hare, caribou, and musk ox (
Ovibos moschatus ). Although caribou have the greatest
herbivore biomass, lemmings, which breed throughout the
year, may reach densities as great as 125 to 250 per hectare;
they consume three to six times as much forage as caribou
do.
• The major Arctic carnivore is the wolf, which preys on musk
ox, caribou, and, when they are abundant, lemmings.
Mediumsized to small predators include the Arctic fox (
Alopex lagopus ), which preys on Arctic hare, and several
species of weasel, which prey on lemmings.