Plant Ecology - Chapter 18 Biomes. Terrestrial biomes Defined by the physiognomy of the predominant...
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Transcript of Plant Ecology - Chapter 18 Biomes. Terrestrial biomes Defined by the physiognomy of the predominant...
Plant Ecology - Chapter 18
Biomes
Terrestrial biomes
Defined by the physiognomy of the predominant vegetation
Boundaries?
No sharp boundaries between biomesIntergrades
Importance of climate
Prevailing climate is most important factor in determining what kind of biome will develop
Precipitation, temperature are most important
Desert biomes
<10 inches (<25.4 cm) of rain per yearCoolTemperateTropical
Grassland biomes
10-30 inches (25.4-76.2 cm) of rain per yearTundraTemperate grasslandTropical savanna
Forest biomes
>30 inches (>76.2 cm) of rain per yearTaiga or coniferous forestTemperate deciduous forestTropical rain forest
Climatograph
Climatograph
Temperature, precipitation not sole determinersOverlap among different biomes on plot suggests that other factors also are important
Seasonality of precipitationTemperature fluctuations around meanSoil composition (based on geology)
Deserts
Lands where evaporation exceeds rainfallHigh evaporation rate
7-50X precipitation
Deserts
Occur in 2 distinct belts between 15-35° N & S latitudeResult primarily from worldwide circulation of air masses (dry over deserts)~25% of world’s land mass
True deserts
<10 inches of rain per yearSemi-deserts may have 2-3X that, but have high evaporation rates
Low humidity results in very hot days, but cool or cold nightsLife is keyed to rainfall events
Infrequent, but usually heavy when they occur
Desert life
Plants are either drought evaders or drought resistors
Evaders
Plants survive dry periods as seeds, but germinate, grow, and reproduce after rainfall
Resistors
Plants develop deep roots to become independent of rainfall events (woody shrubs) or are succulents to store water in stems (cactus)
Grasslands
Tropical savannas - grasslands with scattered individuals trees
Central S. Amer., Central & S. Africa
Savannas
3 distinct seasonsCool-dry, hot-dry, warm-wetFrequent fires suppress trees, maintain grasses and forbs
Herbaceous, low-growing annuals & perennials (dicots)Regrow from roots or seeds every year
Temperate grasslands
Similar to tropical savanna, but occur in cooler regions
N. Amer. prairie (French for plains)Russian steppeHungarian pusztasS. Amer. pampasAfrican veldt
Temperate grasslands
At one time covered 42% of world land surfaceMuch under cultivation todayExcellent soils
Rich topsoil layer
Temperate grassland climate
High rates of evaporationPeriodic severe droughtRainfall ~25-75 cm/yearToo light to support forest, but too heavy to encourage desert
Temperate grassland grasses
Sod-formingKentucky bluegrass
Bunch grassesBig, little bluestem
Temperate grasslands
Most require periodic fires for maintenance, renewal, elimination of incoming/invading woody growth
Tundra
Northernmost limits for plant growth, and at high altitudesPlants generally low-growing
Mat or shrubby
Arctic tundra
Encircles north pole
Brief warm summers with nearly 24 hrs of sun/dayPresence of permafrostWater-logged soils - low evaporationShrubs, sedges grasses, mosses, lichens
Alpine tundra
At high elevations at all latitudesVariable daylength, many of the same restrictions, plant species
Tropical forests
Equatorial, mean temp. ~25°C, 12 hrs sunlight per dayRainfall highly variable-determines type of tropical forest present
Types of tropical forests
Thorn forests - furthest from equator, prolonged dry season
Tropical deciduous forestMore rainfall nearer equator, distinct wet, dry seasonsLose leaves during dry seasons
Types of tropical forests
Tropical rain forest>250 cm of rain per yearPerpetual midsummer conditionsUninterrupted plant growth
Types of tropical forests
Tropical rain forests
Contain as many species of plants and animals as all other types of ecosystems combined4 mi2 area - 750 species of trees, 1500 species of flowering plants
Tropical rain forests
Typically stratified into 5 layers
Each layer has characteristic plants, animalsMay reach height of 80 m
Tropical rain forest soil
Very poor - little or no topsoilEasily weatheredSubsoil with iron-based clay - lateriteMajor problems with slash-and-burn agriculture
Tropical rain forests today
Deforestation
Deforestation
Loss of forests at present rate will mean disappearance within next 15-25 yearsMajor problems will result from climate change, loss of species of medicinal, economic importance
Temperate deciduous forest
Eastern N. Amer, N. Europe and eastModerate temps., moderate moisture levels
5-6-month growing season
Temperate deciduous forest
Dominated by broad-leaved deciduous treesRelatively nutrient-rich soil provides for good growthTypically have 4 layers present
Ground, shrub, sapling, canopyRich diversity of plant, animal life
Taiga
Boreal forest, coniferous forest
Harsh winters with lots of snow
Taiga
Dominated by conifers - spruce, pine, fir, hemlock
Best suited for short growing season because they are not deciduous
Can carry out photosynthesis whenever temps. rise above freezingNeedle shape, waxy cuticle conserve moisture
Thin, acidic, develop slowlyPine needles break down slowly in cool climate
Taiga soils
Taiga animals
Primarily seed, insect eaters, or those that feed on plants in or near waterSquirrels, birds, elk, moose, deer, beaver, porcupine, grizzlies, wolves