Plant%20Ecology%20-%20Chapter%2018

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Plant Ecology - Chapter 18

• Biomes

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Terrestrial biomes

• Defined by the physiognomy of the predominant
  vegetation

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Boundaries?

• No sharp boundaries between biomes
• Intergrades

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Importance of climate

• Prevailing climate is most important factor in
  determining what kind of biome will develop
• Precipitation, temperature are most important

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Desert biomes

• lt10 inches (lt25.4 cm) of rain per year
• Cool
• Temperate
• Tropical

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Grassland biomes

• 10-30 inches (25.4-76.2 cm) of rain per year
• Tundra
• Temperate grassland
• Tropical savanna

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Forest biomes

• gt30 inches (gt76.2 cm) of rain per year
• Taiga or coniferous forest
• Temperate deciduous forest
• Tropical rain forest

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Climatograph
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Climatograph

• Temperature, precipitation not sole determiners
• Overlap among different biomes on plot suggests
  that other factors also are important
• Seasonality of precipitation
• Temperature fluctuations around mean
• Soil composition (based on geology)

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Deserts

• Lands where evaporation exceeds rainfall
• High evaporation rate
• 7-50X precipitation

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Deserts

• Occur in 2 distinct belts between 15-35 N S
  latitude
• Result primarily from worldwide circulation of
  air masses (dry over deserts)
• 25 of worlds land mass

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True deserts

• lt10 inches of rain per year
• Semi-deserts may have 2-3X that, but have high
  evaporation rates
• Low humidity results in very hot days, but cool
  or cold nights
• Life is keyed to rainfall events
• Infrequent, but usually heavy when they occur

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Desert life

• Plants are either drought evaders or drought
  resistors

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Evaders

• Plants survive dry periods as seeds, but
  germinate, grow, and reproduce after rainfall

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Resistors

• Plants develop deep roots to become independent
  of rainfall events (woody shrubs) or are
  succulents to store water in stems (cactus)

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Grasslands

• Tropical savannas - grasslands with scattered
  individuals trees
• Central S. Amer., Central S. Africa

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Savannas

• 3 distinct seasons
• Cool-dry, hot-dry, warm-wet
• Frequent fires suppress trees, maintain grasses
  and forbs
• Herbaceous, low-growing annuals perennials
  (dicots)
• Regrow from roots or seeds every year

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Temperate grasslands

• Similar to tropical savanna, but occur in cooler
  regions
• N. Amer. prairie (French for plains)
• Russian steppe
• Hungarian pusztas
• S. Amer. pampas
• African veldt

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Temperate grasslands

• At one time covered 42 of world land surface
• Much under cultivation today
• Excellent soils
• Rich topsoil layer

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Temperate grassland climate

• High rates of evaporation
• Periodic severe drought
• Rainfall 25-75 cm/year
• Too light to support forest, but too heavy to
  encourage desert

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Temperate grassland grasses

• Sod-forming
• Kentucky bluegrass
• Bunch grasses
• Big, little bluestem

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Temperate grasslands

• Most require periodic fires for maintenance,
  renewal, elimination of incoming/invading woody
  growth

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Tundra

• Northernmost limits for plant growth, and at high
  altitudes
• Plants generally low-growing
• Mat or shrubby

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Arctic tundra

• Encircles north pole
• Brief warm summers with nearly 24 hrs of sun/day
• Presence of permafrost
• Water-logged soils - low evaporation
• Shrubs, sedges grasses, mosses, lichens

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Alpine tundra

• At high elevations at all latitudes
• Variable daylength, many of the same
  restrictions, plant species

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Tropical forests

• Equatorial, mean temp. 25C, 12 hrs sunlight per
  day
• Rainfall highly variable-determines type of
  tropical forest present

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Types of tropical forests

• Thorn forests - furthest from equator, prolonged
  dry season

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Types of tropical forests

• Tropical deciduous forest
• More rainfall nearer equator, distinct wet, dry
  seasons
• Lose leaves during dry seasons

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Types of tropical forests

• Tropical rain forest
• gt250 cm of rain per year
• Perpetual midsummer conditions
• Uninterrupted plant growth

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Tropical rain forests

• Contain as many species of plants and animals as
  all other types of ecosystems combined
• 4 mi2 area - 750 species of trees, 1500 species
  of flowering plants

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Tropical rain forests

• Typically stratified into 5 layers
• Each layer has characteristic plants, animals
• May reach height of 80 m

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Tropical rain forest soil

• Very poor - little or no topsoil
• Easily weathered
• Subsoil with iron-based clay - laterite
• Major problems with slash-and-burn agriculture

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Tropical rain forests today

• Deforestation

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Deforestation

• Loss of forests at present rate will mean
  disappearance within next 15-25 years
• Major problems will result from climate change,
  loss of species of medicinal, economic importance

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Temperate deciduous forest

• Eastern N. Amer, N. Europe and east
• Moderate temps., moderate moisture levels
• 5-6-month growing season

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Temperate deciduous forest

• Dominated by broad-leaved deciduous trees
• Relatively nutrient-rich soil provides for good
  growth
• Typically have 4 layers present
• Ground, shrub, sapling, canopy
• Rich diversity of plant, animal life

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Taiga

• Boreal forest, coniferous forest
• Harsh winters with lots of snow

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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 freezing
• Needle shape, waxy cuticle conserve moisture

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Taiga soils

• Thin, acidic, develop slowly
• Pine needles break down slowly in cool climate

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Taiga animals

• Primarily seed, insect eaters, or those that feed
  on plants in or near water
• Squirrels, birds, elk, moose, deer, beaver,
  porcupine, grizzlies, wolves