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Terrestrial biomes of the world Lecture Topics:. Biome concept Biome classification, distribution Biome climate patterns (Walters Diagrams) Biome survey/distinctive ecological characteristics. Introduction to biome concept. Classification systems Holdridge’s Life Zone system

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terrestrial biomes of the world lecture topics
Terrestrial biomes of the world Lecture Topics:
  • Biome concept
  • Biome classification, distribution
  • Biome climate patterns (Walters Diagrams)
  • Biome survey/distinctive ecological characteristics
introduction to biome concept
Introduction to biome concept
  • Classification systems
    • Holdridge’s Life Zone system
    • Whittaker’s classification scheme based on annual precipitation, temperature (nine biomes recognized)--simpler for purposes here of describing basic biomes
walter climate diagram generic
Walter climate diagram: generic

Ecosystem water-limited if temperature line (red) exceeds precipitation line (blue)

White zone denotes frozen conditions, inhospitable for life

Effective growing season (temperature above 0 ºC)

temperate forest physical environment
Temperate forest physical environment
  • Found at temperate latitudes, typically 40-60º latitude
  • Climate highly seasonal:
    • Cool winter & warm summer, plentiful precipitation all year
    • Cold makes water unavailabledeciduous foliage (leaf drop), brilliant fall colors (depending on species)
    • Spring flush of leavesabundant herbivores (caterpillars,etc.) and migratory birds that feed on them
  • Vernal herbs flower in spring, where forest floor warms up before trees leaf-out (e.g., sweet white violet)
  • Different subtypes of biome
    • Northern hardwoods—e.g., sugar maple, yellow birch
    • Southern hardwoods—oaks, sweet gum, tulip poplar, & evergreens (magnolias, live oak, and pines).
    • Southern pinewoods on poor, sandy soils; fire important
examples of temperate seasonal forest
Examples of temperate seasonal forest

Louisiana examples: Bottomland hardwoods, upland mixed-mesophytic (coniferous & deciduous) forest

temperate rainforest characteristics
Temperate rainforest characteristics
  • Found at temperate latitudes, typically 40-60º (Northwestern U.S., S. Chile, E. Australia, New Zealand)
  • Climate moderately seasonal:
    • Mild winter (below freezing) versus warm to hot summer,
    • Abundant winter rain
    • Summer fog
  • Plants dominated by giant needle-leaved trees (in U.S.: redwoods, western hemlock, douglas fir, western cedar)
    • Ancient, formerly widespread forest type
    • Why giant trees? Year-round growing season, abundant moisture, strong potential evapotranspiration all contribute
physical environment of temperate grassland desert biome
Physical environment of temperate grassland/desert biome
  • Typically 25-50º N, S of equator
  • Climate characterized by high rate evaporation (often warm temperatures), & periodic severe (summer) droughts
    • Rainfall 25-70 cm annually, too little to support forest
    • Often subject to fire—e.g., prairie , longleaf pine (essentially prairie with scattered pine trees)
    • Steppes are cold deserts, dominated by shrubs & grassland
  • Plants—1º productivity proportional to rainfall
    • Grasses dominate (because they’re competitive over trees where fire, grazing predominate)
    • High degree spatial heterogeneity in plants, due to topography, soils, fire history, animal activity (e.g., prairie dogs, bison)
physical environment plants of woodland shrubland biome
Physical environment & plants of woodland/shrubland biome
  • Location (30-40º N, S of equator)
    • Mediterranean region, coastal California, Chile, southern S. Africa, south-western Australia
  • Climate “Mediterranean” (mild, wet winter; hot, dry summer = drought)
  • Plants
    • Fire adapted, dense evergreen shrubs
    • Often deeply rooted, to get at scarce (summer) water
    • Sclerophyllous (waxy, drought-resistant) leaves
    • Aromatic compounds that dissuade insect herbivores
examples of woodland shrubland vegetation
Examples of woodland/shrubland vegetation

Vegetation type also known as matorral (Chile)

physical characteristics of deserts
Physical characteristics of deserts
  • Evaporation exceeds precipitation (rainfall <30 cm)
  • 20-30º N & S Latitude (subtrop. high pressure zone)
  • Plants adapted to drought (= xerophytes)
    • Small leaves dissipate heat, large edge:area ratio
    • Water-storage mechanisms (e.g., many cacti)
    • Conserve H2O (e.g., CAM photosynthesis, waxy cuticle)
    • Protected against herbivores—spines, aromatic compounds
  • Diverse life-forms of desert plants:
    • Succulents (e.g., saguaro & barrel cactus) store water
    • Ephemerals (annuals) grow rapidly, seed after a rain
    • Phreatophytes (e.g., mesquite, palo verde) deeply rooted
    • Opportunistic perennials (ocotillo) flush leaves, flower after rain
boreal northern coniferous biome
Boreal (northern coniferous) biome
  • Climate & setting
    • Found typically from 50-70º N. Latitude (taiga), south in mts.
    • Cold winter, cool-warm summer, 3-5 mo. growing season
  • Taiga (russian for “land of little sticks”) forms continuous stretches of boreal forest, dominated by trees in species of spruce (Picea), fir (Abies); also known as “spruce-moose” biome
    • Diversity of trees low (1-2 spp./site)
    • Conifers dominate (tolerate cold, photosynthesize whenever it’s warm enough, conical shape sheds snow with minimal branch breakage)
tundra physical environment plants
Tundra physical environment & plants
  • Climate & setting
    • Too cold, windy for trees; short growing season (50-60 days in arctic, up to 180 days in alpine zones at higher elevation)
    • Precipitation generally < 25 cm annually (cold air holds little moisture), “locked up” as snow (unavailable to plants)
    • Only in N. hemisphere, north. edge of all northern continents
  • Plants—grassland & mixed shrubland (some dwarf trees)
    • Often low to ground = warmest microclimate, out of wind (e.g., cushion plants)
    • Lichens often important ground (& rock) cover, important in creating soils by breaking down rocks; alders (Alnus) can be an important nitrogen-fixer
    • Northern bogs characteristic of the wettest spots—dominated by carnivorous plants (animal source of N)
climate setting tropical rainforest
Climate & setting Tropical rainforest
  • Near equator
  • Climate continuously favorable for intense biological activity (abundant rainfall, >400 cm, & high temperatures)
    • Biological interactions (ecologically, evolutionarily) impt.
    • Biological diversity staggering (latitudinal diversity gradient)
  • Diverse plant life forms: trees, shrubs, epiphytes, epiphylls, vines, lianas (woody), ferns, tree ferns
    • Layering of plants prominent: ground layer, shrubs, sub-canopy, continuous canopy, & “emergents” (up to 60 m tall)
  • Some plant adaptations:
    • Buttresses to help prop up often shallow-rooted trees (why?)
    • Oval, waxy leaves with drip-tips (why?)
    • Nutrient scavenging & extremely tight nutrient cycling
tropical seasonal forest savanna
Tropical seasonal forest/savanna
  • Tropical seasonal forest occurs at higher latitudes than rainforest (10-20º N, S)
  • Rainfall less than rainforests (240-400 cm), highly seasonal
    • 3-6 month dry season, often with no rainfall
  • Dry forests have almost as diverse plant and animal communities as rainforests
    • Trees typically drought-deciduous (facultative)
    • Ant-acacia mutualism is characteristic of dry forests of Central America
    • Biome highly threatened by human activities, because of its potential for agriculture, grazing

Acknowledgements: Some illustrations for this lecture from R.E. Ricklefs. 2001. The Economy of Nature, 5th Edition. W.H. Freeman and Company, New York.