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