Presentation on theme: "Terrestrial biomes of the world Lecture Topics:"— Presentation transcript:
1 Terrestrial biomes of the world Lecture Topics: Biome conceptBiome classification, distributionBiome climate patterns (Walters Diagrams)Biome survey/distinctive ecological characteristics
2 Introduction to biome concept Classification systemsHoldridge’s Life Zone systemWhittaker’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
5 Walter climate diagram: generic Ecosystem water-limited if temperature line (red) exceeds precipitation line (blue)White zone denotes frozen conditions, inhospitable for lifeEffective growing season (temperature above 0 ºC)
7 Temperate forest physical environment Found at temperate latitudes, typically 40-60º latitudeClimate highly seasonal:Cool winter & warm summer, plentiful precipitation all yearCold makes water unavailabledeciduous foliage (leaf drop), brilliant fall colors (depending on species)Spring flush of leavesabundant herbivores (caterpillars,etc.) and migratory birds that feed on themVernal herbs flower in spring, where forest floor warms up before trees leaf-out (e.g., sweet white violet)Different subtypes of biomeNorthern hardwoods—e.g., sugar maple, yellow birchSouthern hardwoods—oaks, sweet gum, tulip poplar, & evergreens (magnolias, live oak, and pines).Southern pinewoods on poor, sandy soils; fire important
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 rainSummer fogPlants dominated by giant needle-leaved trees (in U.S.: redwoods, western hemlock, douglas fir, western cedar)Ancient, formerly widespread forest typeWhy giant trees? Year-round growing season, abundant moisture, strong potential evapotranspiration all contribute
13 Physical environment of temperate grassland/desert biome Typically 25-50º N, S of equatorClimate characterized by high rate evaporation (often warm temperatures), & periodic severe (summer) droughtsRainfall cm annually, too little to support forestOften subject to fire—e.g., prairie , longleaf pine (essentially prairie with scattered pine trees)Steppes are cold deserts, dominated by shrubs & grasslandPlants—1º productivity proportional to rainfallGrasses 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)
21 Boreal (northern coniferous) biome Climate & settingFound typically from 50-70º N. Latitude (taiga), south in mts.Cold winter, cool-warm summer, 3-5 mo. growing seasonTaiga (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” biomeDiversity 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)
24 Tundra physical environment & plants Climate & settingToo 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 continentsPlants—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-fixerNorthern bogs characteristic of the wettest spots—dominated by carnivorous plants (animal source of N)
30 Tropical seasonal forest/savanna Tropical seasonal forest occurs at higher latitudes than rainforest (10-20º N, S)Rainfall less than rainforests ( cm), highly seasonal3-6 month dry season, often with no rainfallDry forests have almost as diverse plant and animal communities as rainforestsTrees typically drought-deciduous (facultative)Ant-acacia mutualism is characteristic of dry forests of Central AmericaBiome highly threatened by human activities, because of its potential for agriculture, grazing
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.
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