P1251941330VwCeB

1
Chapter 26 Biomes Different regions of the
earth are known by the dominant vegetation
occupying each region. The dominant vegetation
is maintained by the combined effect of biotic
and abiotic factors. Each such region is called
a biome. Similar biomes have similar
characteristics whether they are located in North
America, South America, Asia, Europe, Africa or
Australia.
2
(No Transcript)
3

• Tundra
• Occupies 20 of the globe above the Arctic Circle
  (Arctic Tundra) and also timberline in mountains
  below the Arctic Circle (Alpine Tundra).
• Very cold, drying winds, freezing temperatures
  throughout most of the year, a short growing
  season (2-3 months) with long periods of
  sunlight, precipitation is less than 10" (25 cm)
  per year.
• - Soil is shallow (5 - 7.5 cm deep),
  nutrient-poor largely organic that is waterlogged
  during growing season. A permafrost layer, 10-20
  cm up to 1 meter deep, prevents water draining.
  No recycling of nutrients due to the cold and
  anaerobic conditions of the soil.

4

• Tundra (continued)
• - Vegetation Grasses, sedges, mosses, lichens,
  and dwarf evergreen species. Plants are usually
  perennials and often reproduce by bulbs,
  rhizomes, tubers or root systems that remain
  below ground.
• - The tundra ecosystem is exceptionally fragile
  and is easily disrupted. It does not restore
  itself quickly when damaged.

5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8

• Taiga (Northern Coniferous or Boreal Forests)
• - Covers the globe just below the Arctic Tundra.
• - Long and cold winters (-50oC or -58oF in mid
  winter) with very short days. Summer temps 20o
  -30oC (68oF - 86oF) with very long days (18 h
  photoperiod).
• - Permafrost occurs in over 65 of the taiga.
  Fires are frequent. Fires melt the permafrost
  and stimulate plant growth for a few seasons.
  Soils are acidic and nutrient-poor.
• - Precipitation mostly in the summer 25 - 100 cm
  (10 30).
• - Vegetation Is dominated by conifer forests
  which include spruce, fir, and pines. To adapt
  to the taiga, conifers have thick-walled
  epidermis, sunken stomata and a thick cuticle.
  Deciduous trees such as birch, poplar willow and
  alder occur in some wetter areas. To adapt to
  poor taiga soils, the alder roots carry
  nitrogen-fixing actinomycetes.

9
(No Transcript)
10
(No Transcript)
11
3. Temperate Deciduous Forests - Cover large
areas in the Northern Hemisphere. In North
America, they occur from the Great Lakes to the
Gulf of Mexico and extend from the Mississippi
River to the eastern seaboard. These forests
also exist in Western Europe and Asia. -
Temperature varies greatly. It falls below 4oC
(39oF) in midwinter and rises above 20oC (68oF)
in summer. Annual precipitation of 50 - 165 cm
(20 65) occurs mostly during the summer. -
Deciduous trees are broad-leaved species e.g.
maples, oaks and hickories. Conifers exist in
areas where soil conditions are favorable. Wild
flowers bloom in the spring before the canopy
excludes the light to the forest floor.
12
Fig. 26.4a
13
Fig. 26.4b
14

• 4. Grassland
• - Located in the heart of the continent. On
  their margins they are surrounded by forest and
  desert biomes.
• Annual precipitation varies greatly 25 cm (10)
  in some parts up to 100 cm (39) in others.
  Temperatures range from -45oC (-50oF) to 45oC
  (113oF).
• Vegetation is grasses (for grazing cattle) and
  cereal crops (corn and wheat). A lot of wild
  flowering plants.
• North American grasslands (prairies) grew on
  fertile soils supporting large herds of migratory
  grazing buffalo.
• - Areas with a Mediterranean climate receives
  most precipitation in the winter, thus grasses do
  not grow as tall as those of Midwestern prairies.
  

15
(No Transcript)
16
Fig. 26.5a
17
Fig. 26.6
18
(No Transcript)
19

• 5. Deserts
• Worlds major deserts are located at 30o N and
  30o S latitude.
• - In the Southwest (Sonoran desert).
• - Very little annual precipitation lt 12.5 cm
  annually or in some parts the soil is too porous
  to retain water.
• - Due to low humidity fluctuation in day/night
  temperatures is very high (15oC 35oC on a hot
  summer day). Very high light intensity and no or
  very little water vapor to filter the sun's rays.
  Plant adaptations
• (i) Crassulacean acid metabolism (CAM) as means
  of photosynthesis. In CAM plants, organic acids
  are formed in their chloroplasts at night. In
  day, carbon dioxide (CO2) is released from the
  organic acids and used by plants to
  photosynthesize. This occurs because stomata are
  closed during the day to reduce transpiration and
  thus no CO2 enters the plants through stomata.
• (ii) Leaves reduced to spines (stems perform
  photosynthesis) or covered with thick cuticle
  e.g. Cacti.
• (iii) Cacti have widespread shallow roots.
• (iv) Special internal structures in stems to
  store water.

20
Fig. 26.7
21

• 6. Mountain and Coastal Forest
• Extends from the Pacific Northwest to the Rocky
  mountains, the Sierra Nevada and California coast
  ranges south.
• Such forests are originally deciduous forests
  that extended west but due to climate change
  (reduced rainfall in summer) the mountain forests
  were formed.
• Very large coniferous trees replaced most of the
  deciduous trees, however, some maples, birches
  and oaks still exist at the bottom of the
  mountains.
• Annual precipitation in some parts exceeds 250
  cm (100) which explains the big size Douglas
  firs. The large redwood trees of California
  depend on fog to reduce transpiration and
  maintain their size. Mountain forests show a
  clear altitudal zonation of species.

22

• Mountain and Coastal Forest (continued)
• Due to the dry summers and frequent forest fires
  some trees are adapted to fires. Example
• (i) The thick bark of Douglas fir can be burnt
  but does not transmit much heat to the internal
  tissues.
• (ii) The giant redwoods of the Sierra Nevada
  can survive after their bark is burnt in a fire.
• (iii) The cones of some pines do not open to
  disperse their seeds until they are exposed to
  fire. (iv) The seeds of some species of pine
  germinate at a higher rate after they have been
  exposed to fire.

23
Fig. 26.8
24

• 7. Tropical Rain Forest
• - Around the equator. Such forests occupy about
  5 of the earth and half the forests.
• Annual rainfall 200 - 400 cm (79 157). There
  is no dry season. Temperatures 25oC - 35oC (77oF
  95oF) humidity is gt 80.
• The number of flora exceeds all the other biomes
  combined. The vegetation is dominated by
  broadleaf evergreen trees (160 ft high) with
  shallow root systems.
• Dense multilayered canopy. Epiphytes such as
  orchids their roots don't touch the ground so
  they grow on rainwater (containing a few
  minerals) accumulating in their leaf bases.
• Poor soils. Nutrients either uptaken by plants
  or leached by heavy rainfall.

25
Fig. 26.9