1. Terrestrial biomes of the world Lecture Topics:
Biome concept
Biome classification, distribution
Biome climate patterns (Walters Diagrams)
Biome survey/distinctive ecological characteristics

2. 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

3. Robert Whittaker’s classification of biomes, based on annual precipitation, temperature

4. Global distribution of biomes

5. 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)

6. Temperate seasonal forest biome

7. 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

8. Examples of temperate seasonal forest
Louisiana examples: Bottomland hardwoods, upland mixed-mesophytic (coniferous & deciduous) forest

9. Temperate rain forest

10. 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

11. Examples of temperate rainforest plants

12. Temperate grassland/desert

13. 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 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)

14. Examples of temperate grassland/desert vegetation
(also known as shrub-steppe)

15. Woodland/shrubland

16. 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

17. Examples of woodland/shrubland vegetation
Vegetation type also known as matorral (Chile)

18. Subtropical desert

19. 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

20. Boreal forest

21. 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)

22. Boreal forest vegetation

23. Tundra biome

24. 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)

25. Some plants of tundra biome

26. Tropical rainforest biome

27. 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

28. Some plants of tropical rainforest biome

29. Tropical seasonal forest biome

30. Tropical seasonal forest/savanna
Tropical seasonal forest occurs at higher latitudes than rainforest (10-20º N, S)
Rainfall less than rainforests ( 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

31. Some trees of tropical savannas

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