IB 105 Lecture 12

communities proceeding through predictable changes through time
climax community
Outcome of succession, stable, long-lasting community
Primary Succession
Primary – begins with total lack of organisms, bare mineral surface, takes longer than secondary
Secondary Succession
Secondary – begins with destruction or disturbance of existing ecosystem
Occurs at extreme northern latitudes,
or high elevations (mountain tundra)
low precipitation (<35cm)
Permanently frozen soil layer = permafrost
Short plants dominate
Waterlogged soils common in summer
Very little water (<25 cm/year)
High evaporation
Large daily temperature fluctuations
Species not very dense
Species have adaptations to hot, dry environment
Desertification: change from fertile land to desert.
results from over grazing, intense agricultural use, erosion, water runoff, and over heating of soil.
Boreal Forest
Also called taiga, northern coniferous forest
Occurs in southern Canada, northern Europe, much of Russia
Short, cool summer; Long harsh winters
Spruce and fir, dominant vegetation
Humid due to precipitation and low evaporation, but winter dry because precipitation is snow
Temperate Deciduous Forest
Occur in eastern half of U.S., south central and eastern Canada, southern Africa, Europe, Asia

Moderate rainfall (75-100 cm), relatively evenly distributed
Warm summers and relatively mild winters
Trees dominant vegetation, type of tree varies geographically

Occur in temperate areas
Also called prairies or steppes
Medium precipitation (25-75 cm)
Hot summers, cold to mild winters
Grasses dominant vegetation
Need fire to prevent invasion of trees, release nutrients
Lots of grazing animals
Wastes fertilize prairies, grazing helps keep out trees
Most grassland has been converted to agriculture
Occurs in Africa, South America, Australia
High rainfall (50-150 cm), but unevenly distributed
Periods of high rainfall, followed by droughts
Temperature warm, relatively constant
Plants dominated by grasses and drought resistant trees
Dominant animals are grazers
Plant and animal reproduction timed around rainy season, when resources least limiting
Mediterranean Shrublands
Also known as Chaparral.
Receives 40-100 cm annual precipitation.
Wet, cool winters and hot, dry summers.
Typical of Mediterranean coast and coastal southern California.
Vegetation dominated by woody shrubs adapted to hot, dry summers.
Fire is a common feature.
Tropical Dry Forest
Annual precipitation ranges 50-200 cm.
Many exhibit monsoon climate.
Rainfall highly seasonal.
Drought resistant plants.
Occur along equator in Central and South America, Africa, Southeast Asia, Caribbean and Pacific Islands
Tropical Rainforest
Temperature warm and relatively constant
Very high rainfall (>200 cm/year)
Rapid growth, but nutrient poor soils
Multi-layered forests of emergent trees, canopy trees, understory trees, shade-tolerant plants, and epiphytes
Most diverse biome on earth