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Terrestrial biomes of the world Lecture Topics: n Biome concept n Biome classification, distribution n Biome climate patterns (Walters Diagrams) n Biome.

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Presentation on theme: "Terrestrial biomes of the world Lecture Topics: n Biome concept n Biome classification, distribution n Biome climate patterns (Walters Diagrams) n Biome."— Presentation transcript:

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

2 Introduction to biome concept n Classification systems u Holdridge’s Life Zone system u 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 Effective growing season (temperature above 0 ºC) Ecosystem water- limited if temperature line (red) exceeds precipitation line (blue) White zone denotes frozen conditions, inhospitable for life

6 Temperate seasonal forest biome

7 Temperate forest physical environment n Found at temperate latitudes, typically 40-60º latitude n Climate highly seasonal: u Cool winter & warm summer, plentiful precipitation all year u Cold makes water unavailable  deciduous foliage (leaf drop), brilliant fall colors (depending on species) u Spring flush of leaves  abundant herbivores (caterpillars,etc.) and migratory birds that feed on them n Vernal herbs flower in spring, where forest floor warms up before trees leaf-out (e.g., sweet white violet) n Different subtypes of biome u Northern hardwoods—e.g., sugar maple, yellow birch u Southern hardwoods—oaks, sweet gum, tulip poplar, & evergreens (magnolias, live oak, and pines). u 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 n Found at temperate latitudes, typically 40-60º (Northwestern U.S., S. Chile, E. Australia, New Zealand) n Climate moderately seasonal: u Mild winter (below freezing) versus warm to hot summer, u Abundant winter rain u Summer fog n Plants dominated by giant needle-leaved trees (in U.S.: redwoods, western hemlock, douglas fir, western cedar) u Ancient, formerly widespread forest type u 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 n Typically 25-50º N, S of equator n Climate characterized by high rate evaporation (often warm temperatures), & periodic severe (summer) droughts u Rainfall cm annually, too little to support forest u Often subject to fire—e.g., prairie, longleaf pine (essentially prairie with scattered pine trees) u Steppes are cold deserts, dominated by shrubs & grassland n Plants—1º productivity proportional to rainfall u Grasses dominate (because they’re competitive over trees where fire, grazing predominate) u 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 n Location (30-40º N, S of equator) u Mediterranean region, coastal California, Chile, southern S. Africa, south-western Australia n Climate “Mediterranean” (mild, wet winter; hot, dry summer = drought) n Plants u Fire adapted, dense evergreen shrubs u Often deeply rooted, to get at scarce (summer) water u Sclerophyllous (waxy, drought-resistant) leaves u 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 E vaporation exceeds precipitation (rainfall <30 cm) n 20-30º N & S Latitude (subtrop. high pressure zone) n Plants adapted to drought (= xerophytes) u Small leaves dissipate heat, large edge:area ratio u Water-storage mechanisms (e.g., many cacti) u Conserve H 2 O (e.g., CAM photosynthesis, waxy cuticle) u Protected against herbivores—spines, aromatic compounds n Diverse life-forms of desert plants: u Succulents (e.g., saguaro & barrel cactus) store water u Ephemerals (annuals) grow rapidly, seed after a rain u Phreatophytes (e.g., mesquite, palo verde) deeply rooted u Opportunistic perennials (ocotillo) flush leaves, flower after rain

20 Boreal forest

21 Boreal (northern coniferous) biome n Climate & setting u Found typically from 50-70º N. Latitude (taiga), south in mts. u Cold winter, cool-warm summer, 3-5 mo. growing season n 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 u Diversity of trees low (1-2 spp./site) u 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 n Climate & setting u Too cold, windy for trees; short growing season (50-60 days in arctic, up to 180 days in alpine zones at higher elevation) u Precipitation generally < 25 cm annually (cold air holds little moisture), “locked up” as snow (unavailable to plants) u Only in N. hemisphere, north. edge of all northern continents n Plants—grassland & mixed shrubland (some dwarf trees) u Often low to ground = warmest microclimate, out of wind (e.g., cushion plants) u Lichens often important ground (& rock) cover, important in creating soils by breaking down rocks; alders (Alnus) can be an important nitrogen-fixer u 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 n Near equator n Climate continuously favorable for intense biological activity (abundant rainfall, >400 cm, & high temperatures) u Biological interactions (ecologically, evolutionarily) impt. u Biological diversity staggering (latitudinal diversity gradient) n Diverse plant life forms: trees, shrubs, epiphytes, epiphylls, vines, lianas (woody), ferns, tree ferns u Layering of plants prominent: ground layer, shrubs, sub- canopy, continuous canopy, & “emergents” (up to 60 m tall) n Some plant adaptations: u Buttresses to help prop up often shallow-rooted trees (why?) u Oval, waxy leaves with drip-tips (why?) u Nutrient scavenging & extremely tight nutrient cycling

28 Some plants of tropical rainforest biome

29 Tropical seasonal forest biome

30 Tropical seasonal forest/savanna n Tropical seasonal forest occurs at higher latitudes than rainforest (10-20º N, S) n Rainfall less than rainforests ( cm), highly seasonal u 3-6 month dry season, often with no rainfall n Dry forests have almost as diverse plant and animal communities as rainforests u Trees typically drought-deciduous (facultative) u Ant-acacia mutualism is characteristic of dry forests of Central America u 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 The Economy of Nature, 5th Edition. W.H. Freeman and Company, New York.


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