chapter 12 - biogeography of the earth

8/8/2019 Chapter 12 - Biogeography of the Earth

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Biogeography ofthe Earth

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CHAPTER 12: Biogeography of the Earth

Sunset in the EvergladesCourtesyU.S. National Park Service

The distribution of biotic systems is related to the variation in climate, soils, and topography

on Earth. Over eons of time, plants and animals have occupied and adapted to the particularenvironmental conditions in which they live. The giant saguaro cactus stores water in fleshystems to nourish itself in the hot desert, while the heavy, shaggy coat of the musk oxen helps

protect it from the cold arctic wind.

The Physical Environment: An Introduction to Physical Geography


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Biogeography of the Earth Outline

Fundamentals of Biogeography andEcology

Biogeography and ecologicalsystems

Biogeographical realms Habitat occupation Habitat Degradation and Human

ActivityEnergy Flow Through Ecosystems

Energy capture and use Photosynthesis

Respiration

Transpiration

Biomass Productivity Trophic Levels and Food Chains

Ecology of Vegetation and Plant Succession Principal Adaptive Strategies of Vegetation Plant communities Principle of Limiting Factors Plant Succession

Earth Biomes Forest Biome

Tropical Forests

Species Endangerment in Tropical Forests Deforestation in Tropical Forests

Midlatitude Forests

Northern Forests

Savanna Biome Tropical Savanna

Thorn Tree Tropical Scrub

Midlatitude Savanna

Human Activities and the Savanna biome.

Grassland Biome Fire and the grassland biome

Desert Biome Dry Desert

Midlatitude Shrub Desert

Desertification

Tundra Biome Arctic

Alpine

Global Warming and Arctic Habitats

Review and Resources

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_fundamentals.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_fundamentals.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_occupation.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_human_activity.htmhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_human_activity.htmhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_eco_energy.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/transpiration.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomass_productivity.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/trophic_levels_and_food_chains.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_ecology.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/plant_communities.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/principle_of_limiting_factors.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/plant_succession.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_link.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_1.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/deforestation_in_the_tropical_forests.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_midlatitude_forests_page_1.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_northern_forest.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_savanna_page_1.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_savanna_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_grassland.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_desert.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/desertification.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tundra.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tundra_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/global_warming_arctic_habitat.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/review.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_fundamentals.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_fundamentals.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_fundamentals.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_occupation.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_human_activity.htmhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_human_activity.htmhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/habitat_human_activity.htmhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_eco_energy.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/transpiration.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomass_productivity.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/trophic_levels_and_food_chains.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biogeography_ecology.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/plant_communities.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/principle_of_limiting_factors.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/plant_succession.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_link.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_1.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/deforestation_in_the_tropical_forests.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_midlatitude_forests_page_1.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_northern_forest.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_savanna_page_1.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_savanna_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_grassland.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_desert.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/desertification.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tundra.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tundra_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/global_warming_arctic_habitat.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/review.html


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Fundamentals of Biogeography and Ecosystems

Biogeography and ecological systems

Biogeography is the study of the geographical patterns of plant and animal species. Tounderstand the distribution of plant and animal species on Earth, a fundamental knowledge ofecology and ecosystem dynamics is required. Ecology is the study of the interactions amongorganisms. An ecosystem is a functioning entity of all the organisms in a biological systemgenerally in equilibrium with the inputs and outputs of energy and materials in a particularenvironment. It is the basic ecological unit of study. There are two kinds of ecosystems,aquatic and terrestrial. An ecosystem is comprised of habitats, biological communities, andecotones.

A biome is often referred to as a global-scale community of plants and animals and is thelargest subdivision of the biosphere. A biome may contain many different kinds of smallerecosystems. Biomes are typically distinguished on the basis of the characteristics of theirvegetation because it makes up the largest portion of biomass. Biomes are subdivided

by formation class, vegetation units of a dominant species.

Plants and animals disburse across the Earth and occupy habitats favorable for their survival.A habitat is the specific, physical location of an organism-- it's where they live. MostAfrican elephants live on savannas and in dry woodlands. Bass prefer a habitat of warm,calm, clear water and is usually found in slow-moving streams, ponds, lakes, and reservoirs.Habitats can be identified at different spatial scales.Macrohabitats are delineated by climateand subdivided on the basis of their vegetation. Microhabitats are smaller in size, such as thehabitat along a stream channel or a layer within the canopy of a rain forest. Each species hasspecific habitat parameters (temperature, moisture and nutrient availability).

Within a habitat, organisms "occupy" a niche. A niche is the function or occupation, of alife-form within a community. An organism's niche incorporates the physical (habitat),chemical, and biological factors that maintains the health and vitality of the organism. Anorganism's interaction with the abiotic factors of its environment (heat and moisture) definesits niche. The food requirements, and those that prey on it, are part of the organism's niche. Aniche, therefore, is the sum of an organism's physiological adaptation to and interaction withits physical environment.

Biogeographical Realms

Habitat occupation may be "limited" due to the ability for plants and animals to dispersethroughout the environment. Even though a habitat is available for occupation, barriers to

diffusion may prevent organisms from inhabiting them. Habitat occupation may depend onseveral factors. First is the location of centers of evolution called biogeographical realms.



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Figure BE. 1 Biogeographical Realms

Biogeographical realms are geographical regions out of which particular assemblages ofplants and animals evolved and dispersed. TheNearctic realm possesses a great diversity ofbiomes including the tundra, grassland, deciduous and coniferous forest, chaparral, and desertbiomes. The Nearctic realm has been separated from Neotropical by deserts, and untilrecently, an absence of a land bridge between them. ThePalaearctic realm is very similar tothe Nearctic in terms of the diversity of biomes including tundra, grassland, deciduous andconiferous forest, chaparral, and desert biomes. The Neotropical realm is dominated by

tropical forests, savannas, and deserts. The Afrotropical realmis inhabited by tropicalforests, savannas, and deserts. It is separated from Palaearctic realm by the Sahara desert;

previously separated by an arm of the sea. The Australian (orAustralasian) realm has adesert core, surrounded by tropical forest and savanna. The Australian realm boasts a uniquevariety of plants and animals as they have evolved in isolation from outside influence.Pouched marsupial mammals, like the Kangaroo, are found in the Australian realm.The Indomalayan realmis nearly exclusively tropical forest. It was isolated from thePalaearctic by the Himalayan Mountains. The Indomalayan realm was previously separated

by a sea lane that has subsequently been closed by continental drift. The Antarcticrealm exhibits a diverse set of ecosystems from temperate forest and grassland in NewZealand to tundra and ice sheets in Antarctica. Many of New Zealand's mammals are like

those frequenting Antarctic shores. Finally theOceanian realmis dominated by tropicalforests. Physical barrier are often the most imposing barriers to diffusion. Impassabletopography, large water bodies, and unsuitable climates are all impediments for the dispersalof plant and species.

Habitat occupation

The effectiveness of an organism to occupy a habitat depends in part on its means oftransportation. Animals must use their own locomotion, while plants disperse by wind,running water, ocean currents, and animals. Thus, climate and topographic barriers are moreof an impediment to animals than plants. For either, continental drift poses a significant

barrier to diffusion. The separation of continents has isolated plants and animals in the past

thus preventing their complete occupation of a suitable habitat. Continental collisions haveopened land bridges for habitat occupation. Sea level changes have similarly affected plant

http://www.nationalgeographic.com/wildworld/profiles/terrestrial_na.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_na.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_pa.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_nt.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_at.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_at.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_aa.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_im.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_an.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_an.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_oc.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_oc.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_oc.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_na.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_pa.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_nt.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_at.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_aa.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_im.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_an.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_an.htmlhttp://www.nationalgeographic.com/wildworld/profiles/terrestrial_oc.html


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and animal distributions. Lowered sea level, as what occurred during the last ice ages,resulted in chains of islands being connected opening migration routes for animal and plantspecies. Sea level rise during post-glacial times isolated habitats. Isolation thus prevented

plant and animal migration. Presently, trends in global warming are affecting the distributionof parasites carrying infectious diseases. In a June 2002All Things Consideredreport it was

noted that malaria-bearing mosquitoes from lower elevations are invading mountain

ecosystems at higher elevations as temperatures rise, affecting Hawaiian bird populations.(4:41)

Figure BE. 2 Influence of sea - level fluctuation ondispersal of species

Sometimes humans aid in the dispersal of plants and animals. Humans have intentionally orunintentionally introduced species into habitats that they would otherwise not have been ableto on their own, sometimes with disastrous effects. The inadvertent introduction of theAfrican Honey Bee in South America is a notable example. Imported to spur production ofhoney by mating with other native species, this aggressive bee was accidentally released.With few natural predators, populations exploded and has migrated to the southern UnitedStates. People have been attacked by swarms of these "killer bees" when disturbing them.Hawaii's biota evolved in relative isolation. But after its discovery by white culture, theinadvertent, and the sometimes purposeful introduction of alien plant and animal species,have endangered Hawaii's native organisms. All Things Considered(NPR) segment fromMarch 21, 2000 "Hawaii Extinction" reports on how Hawaii's geographical isolation makes

its native organisms especially vulnerable to extinction by alien plant and animalintroductions. (12:07)

Habitat Degradation and Human Activity

Habitat encroachment, fragmentation, and destruction has produced a plethora of problems.Habitat destruction is a leading cause of species endangerment. Habitat encroachmentincreases the contact between human populations and animal populations. Shrinking habitatand accessible sources of food from expanding urban and suburban land use have broughtanimals and humans into conflict. The loss of tiger prey and presence of livestock haveincreased attacks on villagers living near tiger habitat in India. Alligators in homeowners

backyards is becoming a more frequent site in Florida as urban sprawl invades the state's

wetlands. Deer are a nuisance in many suburban areas, destroying gardens andposing a threatto motorists.

http://www.npr.org/programs/atc/features/2002/june/warming/http://www.npr.org/programs/atc/features/2002/june/warming/http://www.npr.org/programs/atc/features/2002/june/warming/http://www.npr.org/features/feature.php?wfId=1071880http://www.panda.org/about_wwf/what_we_do/species/problems/human_animal_conflict/index.cfmhttp://money.cnn.com/2005/11/04/news/newsmakers/deer/http://money.cnn.com/2005/11/04/news/newsmakers/deer/http://www.npr.org/programs/atc/features/2002/june/warming/http://www.npr.org/programs/atc/features/2002/june/warming/http://www.npr.org/features/feature.php?wfId=1071880http://www.panda.org/about_wwf/what_we_do/species/problems/human_animal_conflict/index.cfmhttp://money.cnn.com/2005/11/04/news/newsmakers/deer/http://money.cnn.com/2005/11/04/news/newsmakers/deer/


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Habitat encroachment is responsible for the recent emergence of diseases like Ebola as athreat to humans. Intact habitats tend to inhibit the spread of infectious agents. Damaged,altered, and degraded habitats trigger the spread of new and existing diseases to humans.A 2005 United Nations Global Environment Outlook Year Book 2004/5 reported that thedeadly Nipah virus, normally found in Asian fruit bats, is believed to have passed over to

humans. Land clearance for palm plantations brought bats in contact with swine, and thenhumans as their habitat shrunk. The geographic range and seasonality of mosquito-bornediseases like malaria and dengue fever, are very sensitive to changes in climate.

Illegal logging is the greatest threat to the survival of the orangutan. Native to the IndianOcean islands of Sumatra, it is estimated that no more that 60,000 wild orangutans are leftworldwide, half the population that existed a mere 10 years ago.Forest fires, poaching and conversion of jungles to palm plantations have also decimated their

populations. Living in trees, the great apes feed on insects and fruits, and in turn, disperseseeds that regenerate the tropical forests. In spite of government declarations to curb illegallogging, environmental activists blame political corruption, and of will and insufficientresources to halt the multibillion dollar illegal logging activity. ( See also "Species

endangerment in Tropical Forests")

Wildlife Corridors

Wildlife require large areas to seek out food, mates, and nesting sites. Habitat fragmentationrestricts wildlife movement resulting in overcrowding, over exploitation of resources andspecies endangerment. Scientists are attempting to preserve wildlife by creating corridors

between fragmented portions of habitat. Wildlife corridors allow young animals to seek newterritory and maintain gene flow between individual habitats thus improving species fitness.Only recently have scientists been able to show that wildlife corridors work.

Figure BE.3 Wildlife corridors connectcritical habitats in the agriculturalheartland of Iowa. (Courtesy NRCS)

Wildlife corridors like those seen herein Iowa permit animals to exploit a

variety of resources without having tocross unfriendly terrain like roads,lawns, or barren farm fields.

The Terai Arc is a fifty year effort to reconnect 11 national parks in India and Nepal with onecontinuous corridor of protected areas. Preliminary data from the Khata corridor between

Nepal's Royal Bardia National Parkand the Katarniaghat Wildlife Sanctuary of India showuse by tigers and elephants. The presence of Spotted Deer and Wild Boar hoof prints provideadditional evidence of corridor use.

Energy Flow in Ecosystems

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_2.htmlhttp://www.ia.nrcs.usda.gov/news/brochures/ReptilesAmphibians.htmlhttp://www.worldwildlife.org/wildplaces/him/results/results1.cfmhttp://www.south-asia.com/dnpwc/Bardia%20National%20Park/parkindex.htmlhttp://www.epa.qld.gov.au/nature_conservation/community_role/landholders/case_studies/wildlife_corridors/http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_2.htmlhttp://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/biomes_tropical_forests_page_2.htmlhttp://www.ia.nrcs.usda.gov/news/brochures/ReptilesAmphibians.htmlhttp://www.worldwildlife.org/wildplaces/him/results/results1.cfmhttp://www.south-asia.com/dnpwc/Bardia%20National%20Park/parkindex.htmlhttp://www.epa.qld.gov.au/nature_conservation/community_role/landholders/case_studies/wildlife_corridors/


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Energy capture and use

At the base of an ecosystem, primary producers are actively converting solar energy intostored chemical energy. Photosynthesis is the process of converting solar energy, water, andcarbon dioxide into carbohydrates and oxygen. The process occurs in two steps: first light

energy is absorbed by chlorophyll to split a molecule of water releasing hydrogen andoxygen. The second step uses the energy to convert carbon dioxide to carbohydrates.

6CO2+12H2O

Solar Energy--->(chlorophyll)

C6H12O6+6O2+6H2O

The carbohydrate (C6H12O6) can be converted into starch and stored by the plant.Carbohydrate can be combined with other sugar molecules to make cellulose, the basicstructural material of a plant.

Oddly enough, of all the solar radiation striking a plant, only about 1 percent is used inphotosynthesis. The rate of photosynthesis is dependent on several things, especially theamount of light received ... up to a point. As solar radiation increases the rate of

photosynthesis increases. For many plants there is an upper limit to the rate ofphotosynthesis. In some plants as incident solar radiation increases the rate of photosynthesislevels off, or may decrease. The increasing solar energy load causes the plant to be too hotand the need to cool the plant increases. As a result, transpiration takes over as the dominate

plant process. Transpiration, the loss of water from plants, acts to cool the plant by releasinglatent energy. Adequate supplies of water, carbon dioxide and the availability of nutrients inthe soil affect photosynthesis.

Respiration

While photosynthesis builds stored chemical energy in a plant, respirationis the process of"burning" stored chemical energy, basically through oxidation, for maintaining plantmetabolism. During plant respiration, carbohydrates combine with oxygen and is reduced tocarbon dioxide, water, and heat.

C6H12O6+6O2 ---> 6CO2+6H2O+2830 kj

While photosynthesis operates only during day when sunshine is available, respiration goeson both night and day. Plant growth occurs so long as photosynthesis exceeds respiration.

TranspirationTranspiration is the loss of water from plant leaves. Water exits the leaf throughstomata,which are tiny pore spaces in the leaf. The rate of transpiration depends on air temperatureand solar radiation. As pointed out earlier, transpiration is a cooing process for plants whentemperatures or incident light rise too high and cause heating of the plant. Low humidity,often aided by windy conditions, creates a vapor gradient between the plant and the air. Thistoo induces transpiration. Soil factors are important control over transpiration. If the porespace between soil particles are too large the soil will have poor or low soil capillary. That is,the rate of water rise is too low for plants to extract water from the soil and maintain propermoisture supply. Low soil capillary results from soil drying too. Figures below indicateseasonal changes in plant transpiration. During the moist season, ample soil water is available

to line soil particles to aid the movement of soil water upwards to the root zone.



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Figure BE.4 Plant transpiration during wet periods.

However, during the dry season, a dry layer of soil develops beneath the root zone inhibitingthe upward movement of capillary water causing a capillary lag. The plant ultimately wilts asit cannot extract enough water to meet the increasing demand for water during warm seasons.A small soil moisture reserve will inhibit transpiration too.



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Figure BE.6Net productivity of selected environments

Trophic Levels and Food Chains

The biotic elements that comprise an ecosystem fall into one of several trophic levels.The trophic level of an organism is its position in afood chain, the sequence of consumptionand energy transfer through the environment. For example, a simple grazing food chain iscomprised of

Plant -> herbivore -> carnivore

At the base of the food chain lies the primary producers. Primary producers are principallygreen plants and certain bacteria. They convert solar energy into organic energy. Above the

primary producers are the consumers who ingest live plants or the prey ofothers. Decomposers, such as, bacteria, molds, and fungi make use of energy stored inalready dead plant and animal tissues.



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Figure BE.7 Great Lakes food web(Courtesy EPA GLINP)

Two laws of physics are important in the study of energy flow through ecosystems. The firstlaw of thermodynamics states that energy cannot be created or destroyed; it can only bechanged from one form to another. Energy for the functioning of an ecosystem comes fromthe Sun. Solar energy is absorbed by plants where in it is converted to stored chemicalenergy. The second law of thermodynamics states that whenever energy is transformed,there is a loss energy through the release of heat. This occurs when energy is transferred

between trophic levels as illustrated in afood web. When one animal feeds off another, thereis a loss of heat (energy) in the process. Additional loss of energy occurs during respirationand movement. Hence, more and more energy is lost as one moves up through trophic levels.This fact lends more credence to the advantages of a vegetarian diet. For example, 1350kilograms of corn and soybeans is capable of supporting one person if converted to beef.



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However, 1350 kilograms of soybeans and corn utilized directly without converting to beefwill support 22 people!

Ecology of Vegetation and Plant Succession

Principal Adaptive Strategies of Vegetation

Plants evolve a variety of adaptations to the light and moisture availability within a particularenvironment in order to flourish. Plants adaptations include those of leaf form and canopystructure (the roof of foliage formed by the crowns of trees). For instance, a hard, needle leafstructure is an adaptation to extreme temperatures and low moisture status in winter. Theleaves of some rain forest trees have a special joint at the bottom of their stalk that enablesthem to twist and turn to follow the light as the sun passes from east to west over head.Deciduous trees drop their leaves to cut transpiration loss during dry periods and whentemperatures are very cold.

Fleshy "leaves", like those of desert succulents or thick photosynthetic skin like that of thegiant Saguaro cactus helps retain moisture. The Baobab tree, found in the wet/dry tropical

(savanna) climate stores water in its trunk to combat the long drought period experienced inthat climate.

Figure BE. 8 A Baobab tree, with its thicktrunk and large edible fruit, Dakar,Senegal.

(UN/DPI Photo #187250Cby Evan Schneider Used with permission)

Figure BE. 9 Semidesert vegetation of Arizona(Photo Credit: U.S. G.S. DDS21)

Plants have adapted particular root structures to live in arid regions. Deep tap roots drawmoisture hidden deep below the surface while extensive near - surface root systems catchmoisture as it infiltrates into soil. Some desert grasses have rolled surfaces to reduce waterloss from the inner surface and hairs which reduce air movement.



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needleleaf forest and deciduous forest(Wisconsin, U.S.A.) (Photo credit: U.S. ConservationService)

An ecotone is a plant community in a distinct zone of transition between other moreextensive communities. Ecotones vary in scale, from local (between forest and field) toglobal (savannas). Within an ecotone plants of different environmental tolerances oftenintermingle. For instance, grasses adapted to low moisture conditions intermingle withdeciduous trees within a prairie - forest ecotone.

Principle of Limiting Factors

The plants and animals that succeed in occupying a particular niche are those that can easilyadapt to the unique environmental conditions of a site. Each plant and animal in thecommunity has a specific range of tolerance for particular environmental conditions. Climatefactors are the most important influence over the successful establishment of plant and animalcommunities. Two climatic factors are important, sunlight and moisture.

Not only is the amountof sunlight available important but the duration and quality of lightare important too. For instance, at high altitudes the intense ultra violet light may inhibit thegrowth of particular plants. The intensity of light affects photosynthesis and rate of primary

productivity. The duration of sunlight affects the flowering of plants and the activity patternsof animals. The availability of water is important for the survival of most life forms. But

plants require water for a number of life processes like germination, growth and reproductiontoo. Principle of limiting factors says that the maximum obtainable rate of photosynthesis islimited by whichever basic resource of plant growth is in least supply. The availability ofenergy and moisture varies geographically. At high latitudes the limiting factor is generally

energy availability while in low latitudes moisture is the limiting factor to growth. Thediagram below shows the relationship between potential evapotranspiration, a moisture index,climate and vegetation.

Figure BE. 13 Relationshipbetween climate, vegetationpotential evapotranspiration andthe moisture index.



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The figure on the left shows the relationship between potential evapotranspiration (PE), amoisture index (MI), climate and vegetation. Potential evapotranspiration is the optimalamount of water entering the atmosphere as a result of evaporation and plant transpirationwhen there is an unlimited amount of moisture. Because evaporation and transpirationdepend on energy availability, potential evapotranspiration is a measure of energy input. High

values of potential evapotranspiration relate to warm climates while low values to coolclimates. The moisture index is a measure of moisture availability. High values of themoisture index means that plenty of water is available. Combining the two variables,

potential evapotranspiration and moisture index we have a notion of what the climate is likein any part of the diagrams. For instance, high PE and large values of MI are indicative ofwarm and moist climates. Note that tundra and taiga (mostly conifers) are successfullyestablished over a wide range of moisture conditions, from dry to moist, but always in coolenvironments. Other vegetation systems have more narrowly defined moisture andtemperature requirements.

Plants of a particular region have adapted to the temperature and moisture conditions inwhich they live. Most gardeners are familiar withplant hardiness (growing) zone maps. The

zones are based on the minimum temperature experienced and thus tolerated by differentspecies of plants. There have been recent signs that these zones are starting to shift due toglobal warming.

Plant Succession

Figure BE.14 Fireweedreestablishing on the devastatedslopes of Mt. St. Helens. (CourtesyUSGS CVO)

Natural vegetation of a particular

location evolves in a sequence of stepsinvolving different plant communities.The evolutionary process is known

as plant succession. Plant succession usually begins with a fairly simple community knownas a pioneer community. The pioneer community, and each successive community alters theenvironment in such a way to permit new communities to occupy a site. These alterations ofthe environment include changes in site microclimate and soil conditions.

A climax community is the result of a long period of plant succession. Climax communitiesusually exhibit a good deal of species diversity and thus are relatively stable systems.Disturbance renews a successional sequence. Plant succession was renewed after theexplosion of Mt. St. Helens with the subsequent disruption of biotic communities thatinhabited the region. Human disturbance related to tropical deforestation has renewed thesuccessional sequence of plant communities in the tropical rain forest. However,

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this Morning Edition (NPR) segment from April 8, 1996 reports that disappearing forests

poses a threat to the " Biodiversity in Madagascar" (7:15) (RealAudio Required)

Earth Biomes

Earlier, a biome was defined as a large stable terrestrial ecosystem. Classification of biomesvary and no one system dominates biogeography studies. Here five principal biomes, forest,savanna, grassland, desert and tundra are distinguished on the basis of unique plant andanimal communities. Within each biome may be several formation classes, vegetation unitsdefined on the basis of dominate plants in a terrestrial ecosystem. For instance, the forest

biome includes the tropical rain forest, seasonal forest and shrub, Mediterranean woodland,Midlatitude broadleaf deciduous and mixed forests, broadleaf evergreen, and marine westcoast forest to name a few.

Terrestrial Biomes as classified by the World Wildlife FoundationSource: Wikipedia

The Forest BiomeThe forest biome consists of close growing trees with leaf canopies that generally overlap.The overlapping canopy prevents much light from hitting the forest floor. The shadedconditions keeps forest soils relatively moist. Forest require ample amounts of annual

precipitation to support their growth. Forests are found over a wide range of temperatureregimes , from the hot equatorial regions to the cold subarctic. Forests occupy approximatelyone third of land surface though this value is shrinking as humans cut the forest for materialneeds and economic gain.

The Tropical Rain forest

The Tropical Rain forest contains trees standing 30 to 55 meters in height, creating a

continuous canopy of foliage. The enclosed canopy shades the forest floor inhibiting thedevelopment of much undergrowth, creating an open forest formation. Few pure stands of

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trees exist, instead individuals are widely dispersed throughout the forest. Mahogany, teakand other tropical hardwoods are harvested for creating fine furniture. The lush vegetationand great animal diversity should be expected in thetropical rain forest climate.

Figure BE.15 The multistory canopy ofthe tropical rain forest(Congo)(Imagecourtesy FAO)

Peering into the canopy reveals a multi-story appearance of broad leaf, evergreenvegetation called "selva". The typical three-tiered zonation includes an emergent

layerof solitary, giant trees reaching heights of 55 meters (180 ft) for the sunlight theyrequire. Beneath is an intermediate zone (canopy) of continuous foliage 9 to 18 meters (30 to60 ft) high. The forest floor is relatively open as the shade of the closed canopy inhibits plantgrowth. It is a damp and dim world as one walks through the aroma of decaying vegetation.Giant woody vines called "lianas" snake their way up the trunks of trees.Epiphytes ("air

plants"), like the brilliantly colored bromeliad, grow in the hollows of trees or the upper

surfaces of horizontally-growing branches capturing nutrients and moisture from the air.Imagine That! -- "Rainforest Canopy" :NSF/Finger Lakes Productions International

Figure BE.16 Bromeliads clinging to a rain forest tree(Imagecourtesy FAO)

A cloud forest exists on extremely moist mountain slopes abovethe elevation of the true rain forest. The cloud forest differs fromthe rain forest found at lower elevations in that trees are muchshorter and the forest floor is virtually impenetrable.

Plants have adapted to this environment in unique ways:

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The canopy itself, the ceiling of the jungle, is a dense continuous layer of greenery some 6or 7 meters deep. Each leaf is accurately angled to ensure that it will collect the maximumamount of light. Many have a special joint at the base of the stalk that enables them to twistand follow the sun as it swings over head from east to west each day. All except the topmostlayer is screened from the wind, so the around them is warm and humid.

The Living PlanetD. Attenborough

The rain forest is a treasure trove of different animal and plant species. The numerous speciesthat inhabit the rain forests are not well documented. The intense precipitation of the tropicalrain forest climate heavily leaches the soil. Oxisol soil common to the rain forest arerelatively infertile due to intense weathering and a lack of available nutrients. Deforestationand habitat destruction is severely crippling the rain forest ecosystem.

Tropical Monsoon/Seasonal Forest and Shrub

The Tropical Monsoon/Seasonal Forest and Shrub, contains trees of smaller stature thanthose found in the rain forest. The Monsoon forest may include deciduous trees, as well as,

broadleaf evergreen trees reflecting the seasonal precipitation of the monsoon climate. Thetrees of the Monsoon Forest have a more open canopy than the rain forest, creating a dense,closed forest at the floor, or what we think of as a "tropical jungle" beneath. The thick surfaceundergrowth makes it difficult to navigate through the forest. Jungle growth is also foundalong streams, and in openings created by humans.

BE.17 Monsoon forest of India(Image courtesy FAO)

Like the tropical rain forest, the monsoon forestsupports a diversity of plant and animal species.And like the rain forest, it's biotic system is

being stressed by human activities.

Species Endangerment in the Tropical Forests

Habitat encroachment and destruction have been a primary cause of declining animal andplant species, threatening many with extinction. For example, habitat encroachment and sporthunting has led to the rapid decline of the Bengal tiger and are considered a threaten species.Solitary animals, tigers can weigh up to 500 pounds and measure nine feet in length. Themain diet of the tiger consists of deer, antelope, and wild pig.

Figure BE. 18Northern Tiger(Image courtesy FAO)

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Logging and agriculture in the densely populated countries of southeast Asia have literallysqueezed the tiger out of its home. Human encroachment on the tiger's habitat has led to morefrequent conflicts between tigers and humans. However, human fatalities from tigers are aresult of injured or sick animals to weak to hunt wild animals.

Sport hunting and killing to use body parts for traditional medicines since 1900 hassignificantly contributed to the decline of the tiger. In the early 1900's it was estimated that100,000 tigers roamed Asia. In 1900, approximately 40,000 lived in India. By the 1960's thisnumber fell to 4,000. By the early seventies fewer that 2,000 remained in India. Recognizingthe potential loss of their national treasure, intensive conservation efforts by the Indiangovernment and the world community has doubled their numbers in recent years. The world-wide population of tigers is estimated to be 5,100 to 7,500 individuals (World Wildlife Fund).

Illegal hunting to support the bush meat trade has taken a devastating toll on animal species.The bushmeat trade ranks among the greatest threats to tropical wildlife according to someenvironmentalists. Research has shown that increased poaching in Ghana has resulted in

significant declines in 41 wild animal species. This research speculates that the bushmeattrade has grown partly in response to over fishing off West Africa by foreign and domesticindustrial fleets. With dwindling resources for protein, people turn to the forest for food.

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Deforestation in the Tropical Forests

Figure BE.19 Land clearingfor agriculture onsteep slopes inUganda (CourtesyFAO).

Human activity hasdrastically alteredthe naturaldistribution offorests throughhistory.

Deforestation and habitat destruction is severely crippling the rain forest ecosystem. Rainforests are being destroyed at a rate of 78 million acres (31 million hectares) per year; an arealarger than Poland. With habitat destruction comes loss of species. The World Resources

Institute predicts that deforestation rates of 15 million hectares would reduce species in theclosed canopy forests by 35% by 2040. In Brazil, the estimated average rate of destruction

between 1979 - 1990 was 5.4 million acres per year. In 2003 a record 10,000 square miles ofBrazil was cleared (Lobe, 2004).

Deforestation causes a multitude of effects on the natural environment as shownbelow. Vegetation is degraded due to a loss of nutrient-rich litter and microorganisms todecompose organic matter. The loss of shade accelerates leaching, soil erosion and drying.The hard surface caused by baking impedes water infiltration causing excess runoff andflooding. In addition to the effect on the local vegetation and hydrology, forestremoval impacts atmospheric composition, evapotranspiration, and precipitation.

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Figure BE.20 Effects of deforestation (afterDrew,1983)

Soil degradation from forest clearing for agriculture happens quickly. Soil fertility can

decrease by 80% in only a few years after forest removal.Table BE.1 Soil fertility loss due to forest clearing (Drew,1983)

Soil Characteristics (%)

Land useOrganicContent

CationExchangeCapacity

Nitrogen Phosphorus

Virgin Forest 100 100 100 100

1 Year after clearing,

unused 104 82 66 120

After 2 years cultivation 46 51 36 75



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Government policies in some countries have fostered the exploitation of forest resources.Encouraging the population to develop forest land has opened the forest to continueddegradation. In the 1990's the Bolivian Government began a large-scale program to increasethe rate of forest removal for commercial agriculture (primarily soy and sugar cane, but alsococoa) on the Amazon Basin side of the Andean highlands. The dramatic effect of this actionis seen in Figures BE21a and BE21b. Forest clearings began as small tracts perpendicular toaccess roads taking on a herringbone pattern when seen from the Space Shuttle in 1995. By2008, the cleared area has greatly expanded. The impact of clearing on soil erosion andstream sediment load is evident in the brown, silt-laden Rio Parapet that flows through theregion.


Figure BE. 21a Bolivian forest clearing (1995)along the Rio Parapet in Bolivia (south of SantaCruz, not shown) Courtesy NASA EOS (Source)

Figure BE. 21b Bolivian forest clearing(2008) along the Rio Parapet in Bolivia(south of Santa Cruz, not shown) Courtesy

NASA EOS (Source)
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Figure BE.22 The heavily eroded BetsibokaRiver watershed of in NW Madagascarempties into the Bay of

Bombeteka. (CourtesyNASA)

The heavy seasonal rain of the monsoonforest poses a great danger, generating rapidrunoff, mudflows and flash flooding. Aresult of unregulated deforestation, rivers

become choked with sediment degrading theaquatic environment.

Deforestation has had a significant impact on indigenous cultures too. Six to nine millionindigenous people inhabited the Brazilian rain forest in 1500. Today less than 1% of Brazil's177 million people are full-blooded indigenous Indians (Source: US State Department). Theloss of indigenous cultures destroys a wealth of knowledge about the environment in whichthey lived.

Midlatitude Forests

Mediterranean Woodland

The Mediterranean woodland is a sclerophyll forest consisting of low branching trees withsmall hard leaves and gnarled thick bark. The Mediterranean Woodland is found on westcoast of continents in the midlatitudes and bordering the Mediterranean Sea, in closeassociation with the Mediterranean (Dry Summer Subtropical) climate. Mediterraneanwoodland in North America is found along much of coastal southern California. Thick barkand small, waxy leaves are two adaptations to prevent excessive loss of moisture during thesevere summer drought experienced in the dry summer subtropical climate. Chaparralvegetation grows to a height of 1 to 3 meters and has leathery leaves to prevent moisture loss.Chaparral is adapted to wildfires common in this environment (see below). Canopy of thetypically hardwood, evergreen vegetation covers about 25 to 60 % of the terrain. Thesparseness of the vegetative cover is due to the severe summer moisture stress and human

disturbance.

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Figure BE.26 Mixed forest of Wisconsin, USA.(Source: M. Ritter)

The midlatitude broadleaf deciduous and mixed

forest has been drastically changed over time byhuman activities. By A.D. 1000, China wasvirtually "treeless". Much of England's forests had

been cut by 1700. Today, acid rain threatens thetemperate forest in many locations.

Subtropical Evergreen Forest

There are two variants of the subtropical evergreen forest, the broadleaf evergreen andneedleleaf subtropical forest. The subtropical broadleaf evergreen forest is found in NewZealand, southeastern Australia, and Southern Chile. Here, mild maritime air masses keepconditions moist enough to suppress any summer drought and provide temperatures warmenough to prevent a threat of frost. Small pockets of broadleaf evergreen species likeevergreen oak and magnolia, are found in the United States in Florida and along the GulfCoast.

The subtropical needleleaf forest is found as a southern pine forest in the southeastern UnitedStates. The forest has developed on the sandy deposits along the fridge of the Atlantic andGulf Coasts.

Figure BE. 27 Broadleaf evergreenforest, New Zealand's South Island.(Photo credit: T. Dewyler)



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Temperate Rain Forest (Marine West Coast Forest)

The temperate rain forest, or sometimes known as the Marine West Coast forest, is knownfor its lush vegetation occurring along narrow margins of the Pacific Northwest in North

America. However, the temperate forest lacks thediversity that the tropical rain forest has. The rainforest of the Pacific Northwest is composed of a

few species of broadleaf and needle leaf trees, hugeferns, and a thick undergrowth. Lying on thewindward slopes of the Cascade and Coast Ranges,this forest receives over a hundred inches a yearin marine west coast climate, as much precipitationas some tropical rain forests.

Figure BE.28 Redwood trees of the Temperaterain forest(Source: Michael Ritter)

The temperate rain forest is home to some of the largest trees and oldest living organisms onearth - the coastal redwoods. Exceeding 200 to 300 feet in height and having diameters over20 feet, these trees can live well over a thousand years. The redwood forest floor is coveredand epiphytes dangle from the trees. The cool and shady redwood forests of North Americacreate a habiat for a variety of animals, including the northern spotted owl, Stellar's Jay,

banana slugs, Pacific tree frog, and black bear.

Old growth forests of Douglas fir, spruce, cedar and hemlock have been devastated bylogging. With only 10% of the original forest left, biodiversity loss is a great concern toecologists.

The Northern Coniferous Forest

The northern coniferous forest of the Subarctic climate, also known as the boreal forest, isdominated by coniferous trees, with hardy deciduous trees like birch mixed in. To the south

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lies the temperate forest and the north the tundra. An ecotone found between northernconiferous forest and tundra vegetation called the taiga . Taiga is a more open form of borealforest with low growing conifers. Historically, the pine forests of North America and Europe

have been an important timber resource.Trees are typically shallow rooted due to

the poor soils (spodosols), rockyconditions, discontinuous permafrost.

Figure BE.29 Snow covered conifers ofthe Northern Coniferous forest. (Source:Tom Smylie U.S. Forest Service)

Coniferous forests (taiga) circles the globe and contains a third of all the trees on earth. Onit's northern edge the growing season is a mere one month long. It's a silent world, lackingmany animal species as there is little palatable food, the moose can .. the resinous leafsreduces water loss but makes them quite distasteful to most animals.

Trees in the northern coniferous forest primarily possess pine needles instead of broad leaveslike those of the temperate forests to the south. Needles are an important adaptation to theextreme conditions present in the climate of the boreal forest. Pine needles contain very littlesap, so freezing is not much of a problem. Being dark in color they absorb what little light

falls on their surfaces. The sloping sides of the conical canopy helps catch the low angle sunrays typical of high latitude locations. Usually there is only one tree layer creating a shadingeffect that precludes the growth of any lower tree layers.

Figure BE.30 Birch intermixes withspruce in an open canopied NorthernConiferous forest.(Source:H. Peter WingleU.S. Forest Service)

Retaining their needles at the end of eachgrowing season gives the tree a head startat growth during the spring as they do not have to waste their energy in producing newfoliage. Pine needles have a unique structure which limits the loss of water, a preciouscommodity in this environment. Pine needles have fewer stomata than broadleaf tree leaves.The stomata are recessed into pits on the needle and aligned in a groove on its underside. Thegroove in the needle creates a small layer of still air which slows the loss of water vapor bydiffusion. Water loss is further reduced by the thick waxy coating common to pine needles.

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Water is "shut off" from the tree when the ground completely freezes. Under thesecircumstances the stomata close-up to prevent loss of water from the tree.

Conifers possess a shallow, extensive, yet compact, network of roots. Waxy, resinous needlesand low bacterial activity in the cold subarctic climate combine to produce a thick mat ofundecayed litter on the forest floor. Soils (spodosols) are poor and acidic since few nutrientsare released into the soil. Filamitous fungi surrounding the root ball extend hairs into theneedles lying at the surface, breaking them down into substances usable by the trees. Food forlarger animals is sparse in such an ecosystem and they are likely found where wind throw orfire has created openings in the forest for deciduous shrubs such as birch, aspen and willow toinvade colonize.

Figure BE.31 Close-up of spruce needlesdamaged by acid rain(Source: U.S. Forest Service)

Much of the northern coniferous forest ofEurope and the eastern United States hassuffered from the affects of acid

deposition.Acid deposition refers to the depositing of acids in both solid and liquid form. Themost common form of acid deposition is acid rain. Much of the source of sulfur is from

industrial activities. Acid rain forms when sulfur compounds combine with water in theatmosphere to form sulfuric acid. Acid rain can severely damage the structure of pine needlesmaking them vulnerable to invasion by other diseases and organisms. Soils in which the

plants grow are acidified, mobilizing soluble metals in the soil water and proving toxic toplant roots.

Figure BE.32 Acid damaged forest in thenortheastern United States(Source: U.S. Forest Service)

For many years, scientists suspected thatacid rain could damage forest ecosystems.It wasn't until relatively recently that theyhave for direct evidence to support their suspicions. Find out how in thisAll ThingsConsidered(NPR) segment from October 28, 1999 about scientist's direct link between forest

degradation and acid rain. (3:49) (RealAudio Required)

The Savanna Biome

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The Savanna biome is characterized by an extensive cover of grasses with scattered trees. Itis a transitional biome between those dominated by forests and those dominated by grasses.The Savanna biome is associated with climates having seasonal precipitation accompaniedwith a seasonal drought. A midlatitude variant, the parkland, is located in the drier portions ofthe humid continental climate.

Tropical Savanna

The tropical savanna is generally found in regions dominated by the Wet-Dry Tropicalclimate. An extensive cover of tall grasses, sometimes reaching a height of 3 meters, is foundin the tropical savanna. Most savanna grass is coarse and grows in tufts with intervening

patches of bare ground. Scattered, individual trees or small groves of trees are common. Theumbrella shaped Acacia tree is a notable species of the Savanna biome. Trees do notdominate the biome because the small amount of high sun rainfall is not enough to sustainsuch vegetation. In eastern Africa where precipitation is higher, savanna vegetation ismaintained by periodic fires. Fires burn back the forest and stimulates the growth of grasseslike that which occurs in the prairie grasslands. Savannas, like those found in Venezuela and

Brazil, develop on soils that have a hard crust and are subject to cracking. Tree flourish wheretheir roots can follow the cracks down to water held deep beneath the surface. Grasses growin the crust above.

Figure BE.33 The Baobab tree found in the Savanna ofSenegal.(Source: UN/DPI Photo #187250C by EvanSchneider)

Plants in the savanna have adapted to the long dry seasonin a number of ways. The Baobab tree stores water in itshuge trunk, drawing on the moisture during periods ofdrought stress. Many grasses and trees of the savannaflourish during the brief wet season and then go into a state of dormancy. Grasses turn brown

and trees lose their leaves to reduce the loss of water by transpiration.

A number of different animal species inhabit the tropical savanna like lions, zebras, elephantsand giraffes. The long neck of the giraffe is a unique adaptation to the savanna woodlands; itslong neck permits browsing on the higher foliage of trees.

Thorntree and Tropical Scrub

The Thorntree and Tropical Scrub is characterized by short, thorny trees and shrubs. TreesThe vegetation may form a continuous cover eliminating grasses. This vegetation formationis a response to a longer, and more intense drought period.

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Figure BE.34 Livestock grazing severelydamages the thorntree savanna leading to

problems of desertification. BurkinaFaso*(Picture credit:Carolyn Redenius,United Nations)

The thorntree and tropical scrub hassuffered under the misuse of humanactivity. Overgrazing has reduced the

capacity of the system to withstand the erosive forces of wind, and to a lesser extent water.Without the protective restraint plants, soil and sand, along with valuable soil nutrients, can

blow free from the surface. Deserts are rapidly encroaching and replacing the savannas andsteppe grasslands. Many years of prolonged drought combined with human pressures on the

biome increases the likelihood for desertification of these areas.

Midlatitude Savanna

Figure BE.35 Pinon-Juniper savanna ofnorthern New Mexico.(Photo Credit: T. Detwyler)

A Midlatitude savanna is sometimescalled aparkland. Here, prairie vegetationis broken by patches or ribbons of

broadleaf trees. The midlatitude savanna islocated in a transitional area between the humid continental and midlatitude steppeclimates.Parkland often is a step in the successionary evolution of plant communities on abandonedfarm fields of the eastern United States. For more see "Prairie Parkland (Temperate)Province ".

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Human activities and the savanna biome

Many animals of the savanna biome like the rhinoceros are endangered and threatened withextinction due to hunting and habitat loss. The most species ofelephants ere in danger ofextinction due to poaching for their ivory tusks. Several means to protect these animals have

been tried, even removal of the rhinoceros's horns and the elephant's tusks. Many countrieshave banned the sale of ivory to discourage poaching. But some countries have argued for thetemporary lifting of such bans to sell stockpiled ivory from seizures. Yet lifting such bansmay encourage further poaching. The NPR Morning Edition "Elephant Poaching on the

Rise" segment from Jan. 17, 2000 (5:20) reports on the rise of elephant poaching as aresult of the lifting of the ban on ivory sale for a few African countries.

Figure BE.36 Square lippedrhinoceros, Zambia.

Source: M.Boulton, FAO. Usedwith permission)

The Grassland Biome

The Grassland biome isdominated by grasses of a variety

of species, all having adapted tothe summer drought common to their semiarid habitat. The broad expanse of the grasslands isoccasionally broken by stands of trees. The midlatitude grasslands of have been exploitedmore than any other biome by humans. Ninety nine percent of the United State's tall grass

prairie and 70 percent of the mixed grass and short grass in some states have disappeared.Eight-five percent of the state of Iowa was once covered in native prairie, only one percent isleft. The grasslands, especially the tall grass prairies are the world's most productiveagricultural areas. The famous corn belt of the United States was created on top of the rich

brown mollisolsoils that developed beneath the surface.

The Prairies

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Prairies are found on the humid side of the grassland biome and are often referred to asthe tall-grass prairie. A favorable annual moisture balance supports a dense ground cover of

tall grasses. Grasses range in height between .6 to 1.2 meters (2 to 4 ft.), with some as tallas 8 feet or more on the eastern margin of the

prairies in the United States. In the tall-grassprairie of Iowa, for example, typical grassesare big bluestem and little bluestem; a typicalforb is black-eyed Susan. Trees and shrubsare generally limited to moist sites alongstream channels or hill slopes facing awayfrom the sun. The nutrient - rich soil beneaththe grasslands drew farmers to these regions.

Now, most natural tall-grass prairie has beenreplaced by agriculture. Extensive grasslandsalso occur in Argentina and the Ukraine.

Figure BE.37 Tall grass prairie once common to the eastern Great Plains ofKansas(Courtesy NRCS)

The native grasslands of the world support a diversity of animal life. In North America, largegrazers like the bison roamed the grasslands until hunted to near extinction by settlers movingwest.

Steppe Grassland

On the drier side of the grassland biome lies the steppe grasslands. Vegetation mustcopewith the summer soil moisture deficit common to thesteppe climatein which thisformation class is found. Here, tall grass prairie gives way to grasses smaller than a halfmeter (2 ft).

Figure BE.38 Mixed Tall and Short grassprairie of the U.S. Great Plains.

(Courtesy NRCS)

Toward the drier portions the groundcover becomes sparse with patches ofopen ground found between clumps ofgrass. Overgrazing of the steppe

vegetation leads to accelerated wind erosion and desertification.

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The Kalahari Desert actually isn't a desert under present conditions, though it is covered withmuch sand. It is a fossil desert found in the tropical steppe biome. Parts receive over 250 mmof precipitation, enough to support a cover of vegetation. It is a fossil desert found in thesteppe biome. It' name is derived from the tribal word Khalagari, Kgalagadi or Kalagaremeaning "a waterless place" or the Tswana word Keir, meaning "the great thirst".

Figure BE.39 Wild Pronghorn Antelopecross the short grass prairie ofWyoming.(Courtesy NRCS)Burrowing animals like ground squirrels,

prairie dogs, pocket gophers are commonin the steppe grasslands. Burrowing

predators like the black footed ferret areconsidered an endangered species.

Fire and the grassland biome

Fires, especally those started by lightning, are a natural occurence of the grassland biome.Fire destroys invasive species that compete with grasses. Fire suppression and farmlandconversion have severely disrupted grassland ecosystems. Resource mangers now use

prescribed burning to restore the health of prairie grasslands.

The Desert Biome

The desert biome has the lightest cover of plants of any biome. Lack of moisture preventsplants from establishing themselves in this harsh climate. Many unique adaptations to theextreme heat and lack of moisture enable some plants to survive. Plants adapted to droughtare called xerophytes. Aridisol soils, common to deserts, are typically coarse, lack muchorganic material, and are often weakly developed.

Dry Desert

The dry deserts are typically found in subtropical latitudes and are produced by subsidenceassociated with the eastern sides of the subtropical high. These are extremely dry regions,some places hardly receiving any measurable precipitation during the year. Plant cover isnon-existent over much of the dry desert.

Figure BE.40 Grand ErgOccidental Desert, Algeria(Photo credit: J.Van Acker, FAO

Used with permission)

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Like many dry deserts, a layer ofcoarse material blankets the surface.

This "desert pavement" protects theunderlying surface from erosion.When disturbed, wind easilydislodges particles and transportsthem away in a processcalled deflation. This makes theestablishment of plants very difficult.

Figure BE.41 Desert encroaching ondesert oasis(Photo credit: Mauritania.

I.Balderi,

Plants occur only under the most favorable microclimatic settings like those surroundingan oasis. Oases are created where the water table is near the surface. Groundwater can beeasily extracted to support vegetation and wildlife.

Plant growth and reproduction are quite slow under desert conditions. Surface erosion by

wind or water restricts the establishment of plants. Infrequent storms causes water to sweepacross the barren surface carrying away massive amounts of material along with plants. Therapid movement of sand dunes covers and prevents the establishment of a plant cover too.

Shrub Desert

The Shrub desertof the midlatitudes supports a more diverse community of plants andanimals. Associated with the midlatitude desert climate, more precipitation and coolertemperatures help support a more complete ground cover. This is especially true along drystream beds where moisture is often more plentiful. Large cacti like the Saguaro cactus, andxerophytic shrubs are found in the Shrub desert of North America.

Figure BE.42 Typical vegetation ofshrub desert in Arizona. (Photo Credit:McKee, E.P. 1967, USGS Digital DataSeries DDS-21. Used with permission)

Off-road vehicles and illegal collectingof plants is endangering the shrub desert

of the United States.

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Some xerophytic vegetation are widely spaced, and have extensive root systems to capturemoisture in the soil. Others have waxy leaves or fleshy tissues to store moisture. Enlargedgreen stems like those found on cacti take over the function of leaves in photosynthesis.Some desert vegetation may shed parts of branches during extreme drought.

Additional Reading

American Semidesert and Desert Province

Desertification

Desertification is the expansion of dry lands due to poor agricultural practices (e.g.overgrazing, degradation of soil fertility and structure), improper soil moisture management,salinization and erosion, forest removal, andclimate change.

BE.43 Desertification in AfricaCourtesy FAO

Two common misconceptions prevail aboutdesertification, that it spreads from a desert coreand drought is responsible. Desertification spreads outward from any where excessive abuseof the land occurs and far from any climatic desert. Droughts do increase the possibility ofdesertification if the carrying capacity of non-irrigated land is exceeded. Well-managed land

can recover from the effects of drought. Combining drought with land abuse sets the stage fordesertification.

Cause of Desertification

Desertification comes about by a complex interaction between the natural environment andhuman activities. The cause may vary from region to region on account of economicconditions, population pressure, agricultural practices, and politics. Human activities thatdestroys surface vegetation, degrades soil structure and fertility, impedes water infiltration,and causes soil drying promotes desertification. This is especially true for the fragiletransition zone between arid and semiarid land where human activity has stretched theecosystem to its limit causing expansion of deserts.

Population growth and its demand on agricultural resources has promoted the desertificationprocess. Over cultivation, for example, causes declining soil fertility leading to falling cropyields. Over use leads to crusting of exposed topsoil by rain and sun that increases runoff,water erosion and gullying. Soil drying promotes wind erosion and encroachment of sanddunes on arable land.

Overgrazing has several effects. It:

Causes a decline in pasture vegetation and palatable grass species.

Replaces perennials with short-lived annual species that do not hold soil againsterosion.

Compacts soil under trampling hoofs. Destabilizes dunes when crest vegetation is eaten.

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Forest cutting for fuel wood has deforested large tracks of land in Africa and Asiaencouraging desertification.

Desertification around the world

The United Nations Conference on Desertification ranks desertification hazard on the basis ofa drop in agricultural productivity:

None - less than 10%

Moderate - 10% to 25 %

High - 25% to 50%

Very high - more than 50%

Desertification is a global problem occurring in many places but is prevalent along themargins of semiarid and arid lands in Asia, central Australia, portions of North and SouthAmerica, and Africa. A world map prepared by the United States NRCS shows just how

widespread the problem is.

Figure BE.44 Desertification Vulnerability Courtesy NRCS

Africa has been significantly impacted by desertification. Almost three quarters of Africa'sagricultural drylands are already degraded to some degree. The impact on desertification onthe greatest number of people occurs in Asia. Degraded regions include the sand dunes ofSyria, the eroded mountain slopes of Nepal, and the deforested and overgrazed highlands ofLaos. The Northern Mediterranean region is the cradle of civilization and has borne the

effects of poor agricultural practices. Salinized, infertile soils are the result of natural hazardse.g. droughts, floods and forest fire, as well as overtilling and overgrazing. Soil degradation is

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high through much of Central and Eastern Europe, and very high in some areas, for examplealong the coast of the Adriatic Sea. Poor irrigation practices and the unsustainableexploitation of water resources are contributing to chemical pollution, soil salinization andaquifer depletion. Nearly a quarter of the inhabitants of Latin America and the Caribbean live

below the poverty line fueling practices that lead to land degradation. Erosion and water

shortages are intensifying in many East Caribbean islands.

The Tundra Biome

The Arctic Tundra

We find the arctic tundra biome at high latitudes closely associated with the tundraclimate.Notable areas of arctic tundra are found along the arctic coastal North America,

Europe, Asia and Greenland. Short grasses, flowers, and grass-like sedges, along with coversof mosses and lichens are the dominate forms of vegetation in the tundra. Seasonal frostheave disrupts root systems preventing support for tall vegetation. The arctic tundra lookslike a treeless plain, interrupted by patterned ground and an occasional tree in selectedmicroenvironments.

Figure BE.45 View of the AlaskanTundra.(Courtesy: T. Detwyler)*

Pattern ground shown in figure BE.45 istypical of the tundra landscape. Stone

polygons, soil circles, stone or soil stripesand terraces are common to both arcticand alpine tundra. These features are created by thrusting action of repeated freezing andthawing of moist soil over a solid substrate like rock or permanently frozen ground.Polygonal patterns dominate flat surfaces. Vegetation is usually confined to the stable parts ofthe patterns.

Figure BE.46 Tilted poles on Northwayaccess road, Yukon region Alaska.(Courtesy: USGS Digital Data Series CD-ROM DDS-21)

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Permafrost is a common feature of the arctic tundra climate and biome. Permafrost refers topermanently frozen ground. Actually, the ground has two layers which freeze. A surfacelayer, called the active layer, thaws during the short "summer" and often subsides. Beneaththe active layer is the inactive layer which stays frozen throughout the year. Permafrostcreates a barrier to the root development. Larger trees can grow along better drained river

valleys where the depth to permafrost is greater. The annual freezing and thawing disruptsroot systems inhibiting the growth of very tall vegetation.

Figure BE. 47 Trans-Alaska Pipeline underconstructionCourtesy: United States Fish and Wildlife Service

Permafrost creates an engineering nightmare for

the construction of buildings and otherstructures. You can see in FigureBE.46 how telephone poles have beentilted from the heaving of the surfaceduring freezing and thawing.Much concern for damage to theenvironment was raised over theconstruction of the Trans-Alaska Pipeline.The heated oil running though the pipelineis insulated from the cold permafrost whereit runs underground. In places it zigzagsover the surface on stilts that allow it toexpand and contract with the change in

weather.

Figure BE.48 Musk Ox of the Alaskan arctic tundra.(Courtesy: U.S. Fish and WildlifeService)

The Musk Oxen is a well-known inhabitant of the arctic tundra. A dense fur coat protectsthem from the severe climatic conditions in the tundra. Beneath is a dense fine undercoat thatis fairly waterproof. Adults gather in a protective wall to keep the calves safe from predatorattacks and severe storms. Musk oxen inhabited much of Eurasia and North America duringthe Ice Ages, but now survive only in parts of Greenland and northern Canada.

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The Alpine Tundra

The tundra biome is found at high elevations in mountainous terrain as well. Many, if not all,the same features of the arctic tundra are found in the alpine tundra. Microclimate is animportant control over the distribution of plant species as slope and exposure control the

availability of light and moisture. The landscape is dotted with small cushion plants, lichensand mosses. Willows are found where moisture is abundant. Other factors like soildevelopment, movement of soil by animals, and drainage determine vegetation communitydistribution.

Figure BE.50 Tundra vegetation(Photocredit: Michael Ritter)

Vegetation consists of low growing shrubs,cushion plants, small forbs exploding withcolorful flowers and lush meadows ofsedges and grasses. These plants cover

gentle slopes and rock crevices. Rock surfaces are dotted with a cover of lichens and

mosses. Most species are slow-growing perennials. Plants have been forced to adapt tosuch an extreme environment. Ninety percent of total structure in some plants is in rootsstoring nutrients and energy during poor growing periods. Flowers are often large butother parts of the plant are small to save energy, and reducing exposure to the rigors of thewind. Some plants have waxy coatings or hairs thus losing minimal heat and water to thewind. The location of plant communities is correlated with the duration of snow cover.While snow is blown free from exposed sites, it accumulates in the lee of obstructions andin depressions. Community location is also related to soil, drainage, and movement of soil

by burrowing animals, and frost action which is prevalent throughout much of the alpinetundra. Dense willow thickets often occupy moist depressions on the lee side of ridges. Adeep cover of snow during the winter protects buds from the wind and freezingtemperatures. These are the tallest perennials growing above the krummholz of theecotone.

Figure BE.51 Alpine tundra fell field(foreground) and onrocky knoll ( upperright) Colorado, USA.(CourtesyUNESCO)



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Fell fields are colorful rock gardens exposed to the rigors of the wind. Wind removes snowthroughout the season subjecting the plants to desiccation. Low-lying mats and cushion plantsnestle against the rocky surface.

Figure BE.52 The alpine tundra of NiwotRidge in early May(Photo credit: MichaelRitter)

In the Indian Peaks region of Colorado, the alpine tundra ranges from 11,200 to 12,000 feetdepending on latitude and slope exposure. Plant communities vary significantly in shape and

plant composition, and may vary in size from a few square inches to several acres.

The climate of the tundra is exceedingly harsh. Annual precipitation is around 40 inches,

effective precipitation is far below that amount however. Snow remains as permanent snowfields at some sites. Wind speeds can exceed 100 mph and mean annual temperature is belowfreezing. The frost free season approx. 1 1/2 months. Diurnal temperature ranges are small

because the air is mixed by the constant winds.

Figure BE.53 Solifluction terraces with snow lyingbehind.(Photo credit: Michael Ritter)

Soils are quite variable, frombarely any soils in valleys scouredby glaciers to the mature residualsoils of unglaciated ridges, andscattered in between rocks broughtto surface from frost heave to form

periglacial features likepolygons.Soil ice is found in all soils inwinter, and soil temperatures arelow enough to form patches of

permafrost. A common landscape



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chapter 12 - biogeography of the earth

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