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Plant Ecology - Chapter 18
Biomes
Terrestrial biomes
Defined by the physiognomy of the
predominant vegetation
Boundaries?
No sharp boundaries between biomes
Intergrades
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 year
Cool
Temperate
Tropical
Grassland biomes
10-30 inches (25.4-76.2 cm) of rain per
year
Tundra
Temperate grassland
Tropical savanna
Forest biomes
>30 inches (>76.2 cm) of rain per year
Taiga or coniferous forest
Temperate deciduous forest
Tropical rain forest
Climatograph
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)
Deserts
Lands where evaporation exceeds
rainfall
High evaporation rate
7-50X precipitation
Deserts
Occur in 2 distinct belts between 1535° N & S latitude
Result primarily from worldwide
circulation of air masses (dry over
deserts)
~25% of world’s land mass
True deserts
<10 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
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 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
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
Temperate grasslands
At one time covered 42% of world land
surface
Much under cultivation today
Excellent soils
Rich topsoil layer
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
Temperate grassland grasses
Sod-forming
Kentucky bluegrass
Bunch grasses
Big, 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 altitudes
Plants generally low-growing
Mat or shrubby
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
Alpine tundra
At high elevations at all latitudes
Variable daylength, many of the same
restrictions, plant species
Tropical forests
Equatorial, mean
temp. ~25°C, 12
hrs sunlight per day
Rainfall highly
variable-determines
type of tropical
forest present
Types of tropical forests
Thorn forests - furthest from equator,
prolonged dry season
Types of tropical forests
Tropical deciduous
forest
More rainfall nearer
equator, distinct wet,
dry seasons
Lose leaves during
dry seasons
Types of tropical forests
Tropical rain forest
>250 cm of rain per
year
Perpetual
midsummer
conditions
Uninterrupted plant
growth
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
Tropical rain forests
Typically stratified into 5 layers
Each layer has characteristic plants,
animals
May reach height of 80 m
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
Tropical rain forests today
Deforestation
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
Temperate deciduous forest
Eastern N. Amer, N. Europe and east
Moderate temps., moderate moisture
levels
5-6-month growing season
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
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
freezing
Needle shape, waxy cuticle conserve moisture
Taiga soils
Thin, acidic, develop slowly
Pine needles break down slowly in cool
climate
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