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BIOL 4120: Principles of Ecology
Lecture 22: Biogeographical
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: [email protected]
23 Terrestrial Ecosystems
23.1 Biomes and climate
23.2 Tropical forests (Equatorial zone)
23.3 Tropical savannas (semiarid regions with
seasonal rainfall)
23.4 Desert
23.5 Temperate zone (Mediterranean climate)
23.6 Forest ecosystems (Temperate wetter
23.7 Grassland ecosystems (Temperate zone vary
with climate and geography
23.8 Conifer forests (cool temperature and boreal
23.9 Arctic tundra (cold temperatures and low
Biomes are classified according to
the predominat plant types
Concept of Biomes:
F.E. Clements and V.E. Shelford, 1939
Combining broad-scale distribution of both plants and associated
animals into a single classification
Biomes: classified according to the predominant plant types
Campbell 1996: the world's major communities, classified according to
the predominant vegetation and characterized by adaptations of
organisms to that particular environment.
Major terrestrial biome types:
Tropic forest, temperate forest, conifer forest (taiga and boreal forest),
tropical savanna, temperate grasslands, chaparral (shrublands), tundra,
and desert.
three general plant forms: trees, shrubs, and grasses.
Robert Whittaker,
Cornell Uni.
Biomes and
between biomes
are broad and
often indistinct
Other factors:
topography, soils,
and exposure to
disturbances such
as fire
23.1 Terrestrial ecosystems reflect
adaptations of dominant plant life forms
Why are there consistent patterns in
the distribution and abundance of
three dominant plant life forms that
relate to climate and physical
Terrestrial ecosystems reflect
adaptations of dominant plant life forms
These three forms represent different patterns of carbon
allocation and morphology
Grass: less C to production of supporting tissue (stem) than
do wood plants (shrubs and trees), more to photosynthetic
tissues (leaves)
Woody plants: shrubs allocate lower percentage to stem than
Trees: more to stem, advantage of height and access to light,
cost more for maintenance and respiration.
As environmental conditions become adverse for
photosynthesis (dry, low nutrient, cold T), trees will decline
in both stature and density until they are no longer able to
persist as a component of the plant community.
Within broad classes of forest and woodland ecosystem (trees
are dominant or co-dominant), leaf form is another
plant characteristic.
Based on longevity
Deciduous (live for only one year or growing season)
• Winter-deciduous (temperate regions, low winter T)
• Drought-deciduous (subtropical and tropical, leaf shed on
dry periods)
Evergreen (live beyond a year)
• Broadleaf-evergreen (tropic rainforest, no distinct growing
season, year-round photosynthesis)
• Needle-leaf evergreen (growing season is short or
nutrient availability constrains photosynthesis and plant
Economic model to explain adaptation of leaf form: cost to
produce leaf and gain from photosynthesis.
Ecosystems characteristic
of warm, wet climates with
no distinct seasonality are
dominated by broadleaf
evergreen trees (tropic or
subtropical rain forest).
As conditions become drier,
with a distinct dry season,
broadleaf evergreen habit
gives way to droughtdeciduous trees (seasonal
tropical forest)
As PPT declines further,
trees decline and giving
rise to woodland and
savannas (shrub and
PPT further declines, no
trees can be supported,
giving rise to arid
shrubland and desert.
Similar for T control.
Broadleaf evergreen in
tropic rain forest in
Needle-leaf evergreen in
Sierra Nevada, US
23.2 Tropic rain forest
Location: Equatorial zone between
latitudes 10oN and 10oS
T: warm all year, annual mean
PPT: rainfall occurs daily, min.
Typical example: Amazon basin of
South America
Tropic rain forests in
Amazon (a), Malaysia (b),
and Northeast Australia (c)
High net primary
productivity (NPP)
High diversity of plant and
animal life
7% land surface, >50%
plant and animal species
10-km2 contain 1500
species of flowing plants
and 750 tree species.
Richest area in Malaysia,
7900 species
90% of all primate species live
in the tropical rain forest
orangutan (an arboreal ape)
Gibbons, langurs, macaques
Gorillas, and chimpanzees
Beetles, butterflies
Vertical stratification of a tropic rain forest
Plank-like buttresses
Tropical dry
droughtdeciduous trees
Africa, South
America, Central
Australia, India,
Southeast Asia
Undergo a dry season, influenced by the seasonal migration of Intertropical
Convergence Zone (ITCZ)
23.3 Tropic Savannas
Location: Equatorial zone between
latitudes 30oN and 30oS, Dry tropic
and subtropical.
T: warm all year, annual mean
PPT: distinct seasonality in rainfall,
large interannual variation
Typical example: South America
Tropic Savannas
Savanna: means the treeless areas of South America
An array of vegetation types representing a continuum of
increasing cover of woody vegetation, from open grassland
to widely spaced shrubs or trees to woodland
Occur on land surfaces of little relief, often on old plateaus,
interrupted by escarpments and dissected by rivers
Poor in nutrients, especially P
Dominant species are fire-adapted, subjected to recurrent
Grass cover with or without wood vegetation is always present
Woody component is short-lived (less than a few decades).
Two-lay vertical structure (ground level grass + shrubs or
Support a large and varies assemblage of herbvores,
invertebrate and vertebrate, grazing and browsing.
Interaction between annual PPT and soil texture in defining biomes
Access by plants to soil moisture is more limited on the heavy
textured soils (clay) than sandy oil.
23.4 Desert
Area: 25 to 35%
Location: latitudes between 15 and 30o
Cause: Global air mass circulation
T: High in summer, could be cold in winter
PPT: low, <150 mm
Typical examples: majority in Northern
Hemisphere, Sahara in Africa, Gobi in
Asia, western North America
Deserts are not the same everywhere
Cold desert: Great Basin of North America, the Gobi, Takla Makan, and
Turkestan deserts of Asia
Species: sagebrush, shadscale, chenopods, etc
Hot desert: Mojave, the Sonoran, and Chihuahuan
Vegetation: none to some combination of chenopods, dwarf-shrubs,
and succulents
Hot desert: a. Chihuahuan
Desert, b. Great Victorian
Desert in Australia, c. Dunes
in Saudi Arabian desert.
Survive of desert plants:
Adapted to scarcity of water, low primary productivity
Flowering only when moisture is present
Fast grow, flower, produce seeds and die
Deep-rooted (mesquite, taproots reach water table)
CAM pathway, species leaf structure
Survive of animals
Support a diversity of animal life (bettles, ants, locusts,
lizards, snakes, birds and mammals)
Grazing herbivores: generalists, consume a wide range of
Desert carnivores,such as fox and coyotes, have mixed diet
include leaves and fruits.
23.5 Temperate shrublands
Shrublands: shrub is dominant or codominant, but difficult to categorize
Shrub: no good definition, a plant with
multiple woody, persistent stems but
no central trunk and a height from
4.5 to 8 m.
(Tree can grow less than 8m under
severe environmental conditions)
Temperate shrublands
Location: between latitudes 30o and 40o,
five regions
T: hot dry summers, cool, moist winters
PPT: 65% annual PPT falls during winter
Five regions: semiarid region of western
North America, regions bordering
Mediterranean Sea, central Chile, cape
region of south Africa, south-western and
southern Australia
Chaparral is the dominant
mediterranean shrub vegetation of
southern California
Mediterranean vegetation (fynbos) of
the western cape region of South
23.6 Forest Ecosystems
Forest ecosystems dominate the wetter regions of
the temperate zone
Deciduous forest covered large area of Europe and
China, but mostly converted to croplands, only
exist in eastern China
Southern Hemisphere, temperate evergreen forest
become predominant
North America, deciduous forests consist of a
number of associations (show later)
Asiatic broadleaf forest found in eastern China,
Japan, Korea is similar to the North American
deciduous forest
Large scale distribution
of temperature forest in
eastern US (showed
Temperate forest in fall and spring
23.7 Grassland ecosystems
Rainfall is very important: 250 to 800 mm
Other factors: fire, and human activity
(convert from forest to grassland)
Area: dropped from 42% to <12% of
original size
Location: mid-latitudes in mid-continental
Typical: prairies of North America, steppes
of central Eurasia
Grassland in
Tallgrass prairie
Big bluestem,
Needlegrassgrama grass
Shortgrass prairie
Blue grama and
buffalo grass
a. Tallgrass
prairie in
Iowa, b.
prairie; c.
Aboveground primary productivity is related to MAP (52 grassland)
Grasslands are most productive when MAP>800 mm and MAT > 15oC
23.8 Conifer forests
Conifer forests: needle-leaf evergreen
Location: Northern Hemisphere and mountain
Various composition: wide range of climate they
can grow
Europe: Norway spruce
North America: Rocky: Engelmann spruce,
subalpine fir; Douglas-fir, ponderosa pine,
lodgepool pine; giant sequoia (in California
Boreal forest (11% of Earth’s land surface)
Alaska and Canada in N. America, Euroasia (from
Scotland to northern Japan)
Black spruce in North America
taiga (boreal forest)
Some coniferous forest. A. Norway spruce, b.
Rocky Mountaine subalpine forest, c. montane
coniferous forest in Rocky Mountains
23.9 Arctic Tundra
Tundra is treeless plain
Arctic tundra is a frozen plain, clothed in sedges, heaths, and
willows, dotted with lakes, and crossed by streams
Cold Temperature and low precipitation
Two types:
tundra: up to 100% plant coverage, wet to moist soil
polar desert: dry soil, less than 5% plant cover
Unique conditions:
permafrost: isolate and protect soil OM
vegetation: simple form, slow growth, allocate more to roots
transfer of heat
Principles of Ecology
What we covered in this course:
Ecology is study of interaction of Organisms and environmental
Organisms: adaptation and evolution, life history
Environmental conditions: Climate, terrestrial and aquatic
Subdisplinary of ecology
Population ecology: growth, competition, predation, parasitism
Community ecology: structure and dynamics, influence factors
Ecosystem ecology: Ecosystem energetic, decomposition,
biogeochemical cycle
Global change ecology: climate change and ecosystem researches
Others: biogeography, human ecology
Thank you!