Life on Land

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Life on Land

• Chapter 2

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Natural History The study of how organisms
within a particular area are influenced by
factors such as climate, soils, predators,
competitors and evolutionary history.
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Knowledge of the natural history of organisms is
necessary to preserve and restore natural
ecosystems.
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• Janzen studied natural history of tropical dry
  forests in Costa Rica to aid restoration efforts.
• Guanacaste tree (E. cyclocarpum) has no current
  dependable dispersers, thus trees produce massive
  numbers of fruits.
• Last native dispersers went extinct 10,000 years
  ago.
• Cattle and horses (exotics) now act as dispersers.

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Dispersers of Guanacaste Seeds
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Outline

• Temperature, Atmospheric Circulation, and
  Precipitation
• Climate Diagrams
• Soil Horizons
• Terrestrial Biomes

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Terrestrial Biomes

• Biomes are distinguished primarily by their
  predominant plants and are associated with
  particular climates.
• Geographic and seasonal variations in temperature
  and precipitation are fundamental components.

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Temperature, Atmospheric Circulation, and
Precipitation

• Spherical shape and tilt of earths axis cause
  uneven heating of earths surface.
• Drives air circulation patterns and consequently
  precipitation patterns.
• Warm, moist air rises.
• Cools, condenses, and falls as rain.
• Cooler, dry air falls back to surface.
• Rainforests found near equator.
• Major deserts found near 30o N / S.

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Northern Summer Solstice June 21 Northern
Winter Solstice Dec 21 Spring and Autumnal
Equinoxes March 21 and Sept 22 or 23
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Northern Summer Solstice June 21, the sun is
directly overhead at the 23.5o north latitude
(Tropic of Cancer) Northern Winter Solstice
Dec 21 the sun is directly overhead at the 23.5o
south latitude (Tropic of Capricorn) Spring and
Autumnal Equinoxes March 21 and Sept 22 or 23
the sun is directly overhead at the equator, the
northern and southern hemispheres receive equal
amounts of sunlight.
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At high latitudes in both the southern and
northern latitudes, seasonal changes in solar
radiation Winter low average temperatures and
short day lengths Summers high average
temperatures and long day lengths
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Solar-Driven Air Circulation
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Temperature, Atmospheric Circulation, and
Precipitation

• Coriolis effect causes apparent deflection of
  winds clockwise in the N hemisphere and
  counterclockwise in the S hemisphere.

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Climate Diagrams

• Summarize climatic information using a
  standardized structure.
• Temperature plotted on left vertical axis.
• Precipitation plotted on right vertical axis.
• 10o C equivalent to 20 mm precipitation.
• Relative position of lines reflect water
  availability.
• Adequate moisture for plant growth when
  precipitation above temperature.

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Climate Diagrams
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Soil Foundation of Terrestrial Biomes

• Soil is a complex mixture of living and
  non-living material.
• Classification based on vertical layering (soil
  horizons).
• Profile ( the arrangement of the soil horizons)
  provides a snapshot of soil structure in a
  constant state of flux.

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Soil Horizons

• O horizon Organic Layer freshly fallen organic
  material - most superficial layer.
• A horizon Mixture of minerals, clay, silt and
  sand.
• B horizon Clay, humus, and other materials
  leached from A horizon - often contains plant
  roots.
• C horizon Weathered parent material.

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Soil Profile
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Tropical Rainforests

• Most occur within 10o latitude of equator.
• Little temperature variation between months.
• Annual rainfall of 2,000 - 4,000 mm relatively
  evenly distributed.
• Quickly leaches soil nutrients.
• Mycorrhizae help gather nutrients.
• Organisms add vertical dimension.
• Harbor staple foods and medicines for worlds
  human populations - increasingly exploited.

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Tropical Rainforests
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Tropical Dry Forest

• Usually located between 10o - 25o latitude.
• Climate more seasonal than tropical rainforest.
• Soils generally richer in nutrients, but
  vulnerable to erosion.
• Shares many animal and plant species with
  tropical rainforests.
• Heavily settled by humans with extensive clearing
  for agriculture.

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Tropical Dry Forest
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Tropical Savanna

• Most occur north and south of tropical dry
  forests within 10o - 20o of the equator.
• Climate alternates between wet / dry seasons.
• Drought associated with dry season leads to
  lightning-caused wildfires.
• Soils have low water permeability.
• Saturated soils keeps trees out.
• Landscape is more two-dimensional with increasing
  pressure to produce livestock.

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Tropical Savanna
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Desert

• Major bands at 30o N and 30o S latitude.
• Occupy about 20 of earths land surface.
• Water loss usually exceeds precipitation.
• Soil usually extremely low in organic matter.
• Plant cover ranges from sparse to absent.
• Animal abundance low, but biodiversity may be
  high.
• Strong behavioral adaptations.
• Human intrusion increasing.

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Desert
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Mediterranean Woodland and Shrubland

• Occur in all continents except Antarctica.
• Climate cool and moist in fall, winter, and
  spring, but can be hot and dry in summer.
• Fragile soils with moderate fertility.
• Trees and shrubs typically evergreen.
• Fire-resistant plants due to fire regime.
• Long history of human intrusion.
• Cleared for agriculture.

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Mediterranean Woodland and Shrubland
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Temperate Grassland

• Extremely widespread distribution.
• Annual rainfall 300 - 1,000 mm.
• Experience periodic droughts.
• Soils tend extremely nutrient rich and deep.
• Thoroughly dominated by herbaceous vegetation.
• Large roaming ungulates.
• Bison vs. cattle

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Temperate Grassland
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Temperate Forest (Old Growth)

• Majority lie between 40o and 50o latitude.
• Rainfall averages 650 - 3,000 mm.
• Fertile soils
• Long growing seasons dominated by deciduous
  plants.
• Short growing seasons dominated by conifers.
• Biomass production can be very high.
• Many major human population centers.

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Temperate Forest (Old Growth)
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Boreal Forest (Taiga)

• Confined to Northern Hemisphere.
• Covers 11 of earths land area.
• Thin, acidic soils low in fertility.
• Generally dominated by evergreen conifers.
• Relatively high animal density.
• Historically, low levels of human intrusion.

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Boreal Forest (Taiga)
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Tundra

• Covers most of lands north of Arctic Circle.
• Climate typically cool and dry with short
  summers.
• 200 - 600 mm precipitation.
• Low decomposition rates.
• Supports substantial numbers of native mammals.
• Human intrusion historically low, but increasing
  as resources become scarce.

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Tundra
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Mountains Islands in the Sky

• Built by geological processes and thus
  concentrated in belts of geological activity.
• Climate changes with elevation and latitude.
• Soils are generally well-drained and thin.
• Flora and fauna change with elevation.
• Historically used as a source of raw materials
  for human settlements.

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Mountains Islands in the Sky
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Review

• Introduction
• Temperature, Atmospheric Circulation, and
  Precipitation
• Climate Diagrams
• Soil Horizons
• Terrestrial Biomes

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