Terrestrial biomes of the world Lecture Topics:

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 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)

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 (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

31. Some trees of tropical savannas

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