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Life on Land

Chapter 2

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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.

Predominant plants share similar growth characteristics although species may vary.

Soil types of a biome are often similar due to similar climate and plant type influences.

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Uneven Solar Heating of Earth

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Solar-Driven Air Circulation (convection)

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Temperature, Atmospheric Circulation, and Precipitation

• Spherical shape and tilt of earth’s axis cause uneven heating of earth’s 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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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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Vernal equinox Mar 22nd

Autumn equinox Sept 22nd

Summer solstice June 22nd

Winter solstice Dec 22nd

Seasons due to tilt of the Earth and its annual orbit around the Sun.

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Climate Diagrams

• Mean annual temperature.

• Mean annual precipitation.

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Soil : Foundation of Terrestrial Biomes

• Soil is a complex mixture of living and non-living material.

• Development of soil: Weathering (fracture and dissolution) of

parent rocks and other minerals portions. Organic matter deposition by roots and

litter (leaves, twigs, logs). Infiltration of water leaches material to

deeper layers (horizons) in the soil profile. Climate influences weathering processes.

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Soil Horizons

• O horizon: Organic Layer freshly fallen and decomposing organic material – the most obvious surface layer (humifications begins).

• A horizon: Mixture of minerals, clay, silt, sand, mixed with humus (older dark organic matter – what makes dirt brown).

• 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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Terrestrial Biomes

• Biomes are distinguished primarily by their predominant plants and are associated with particular climates. Tropical Rainforests Tropical Dry Forest Tropical Savanna Desert Mediterranean Woodland and Shrubland Temperate Grassland Temperate Forest (Deciduous & Evergreen) Boreal Forest (Tiaga) Tundra

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Tropical Rainforest

• A broadleaf tropical forest growing in tropical regions where conditions are warm and wet year-round.

• Vertical structure.• Epiphytes

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Tropical Rainforests

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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.• Soils low organic and nutrient poor.

Rain quickly leaches soil nutrients. High decomposition and fast nutrient cycle. Mycorrhizae help gather nutrients.

• Harbor staple foods and medicines for world’s human populations - increasingly exploited.

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Tropical Dry Forest

• Mostly broadleaf forests in tropical regions with pronounced wet and dry seasons where trees drop their leaves during the dry season (“dry deciduous forest”).

• Tropical dry coniferous forests are rare.

http://www.cas.vanderbilt.edu/bioimages/ecoregions/nam-ecoregions-list.htm

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Tropical Dry Forest

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Tropical Dry Forest

• Usually located between 10o - 25o latitude.• Climate more seasonal than tropical

rainforest (wet versus dry)• Soils generally richer in nutrients than

rainforests, 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 Savanna

• Tropical grassland with a few scattered trees; characterized by pronounced wet and dry seasons, with periodic fires.

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Tropical Savanna

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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 in wet season inhibit trees.• Landscape is more two-dimensional with

increasing pressure to produce livestock.

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Desert

• Arid lands occupying 20% of global land area, where evapotranspiration exceeds precipitation for most of the year.

http://helios.bto.ed.ac.uk/bto/desertecology/creosot3.jpg

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Desert

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Desert• Major bands at 30o N and 30o S latitude.• Water loss usually exceeds precipitation.• Soil usually extremely low in organic matter

(lithosols) and often with mineral deposits of calcium carbonate (caliches).

• Plant cover ranges from sparse to absent.• Animal abundance low, but biodiversity may

be high; many are nocturnal and burrowers.• Human intrusion increasing.• Rain shadow quiz.

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Mediterranean Woodland and

Shrubland

• Mild and moist winters and dry hot summers, between 30º and 40º latitude, vegetation is short with small, tough leaves, adapted to periodic fires, found in dry coastal regions (e.g. California chapparal).

http://pix.botany.org/set01/01-110h_700.jpg

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Mediterranean Woodland and Shrubland

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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.

30http://taggart.glg.msu.edu/bs110/PRAIRIE.JPG

Temperate Grassland

Midlatitude grasslands receiving 0.3 to 1.0 m rainfall per year, falling mostly during summers.

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Temperate Grassland

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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

33http://homepages.caverock.net.nz/~bj/beech/sustainable/Forest_floor2.jpg

Temperate Forests

Coniferous or deciduous forests of 40º to 50º latitude with precipitation of 0.65 to 3.0 m per year, with more precipitation in winter than at temperate grasslands.

http://nebraska.sierraclub.org/movalley/images/Hitchcock-Forest.jpg

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Temperate Forest (Old Growth)

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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.

36http://earthobservatory.nasa.gov/Study/BorealMigration/Images/boreal_forest_combined.jpg

Boreal Forest (Taiga)

Northern forest south of the arctic tundra, mostly containing conifers (spuce) and some aspen and birch.

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Boreal Forest (Taiga)

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Boreal Forest (Taiga)

• Confined to Northern Hemisphere. Covers 11% of earth’s land area.

• Thin, acidic soils low in fertility.• Generally dominated by evergreen conifers.• Relatively high animal density.• Historically, low levels of human intrusion.

39http://www.heritage.nf.ca/environment/images/tundra.jpg

Tundra

Northern most biome dominated by mosses, lichens, and dwarfed willows and birch, low to moderate precipitation and very short growing season.

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Tundra

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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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Mountains: Islands in the Sky

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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.• Rare or unique flora and fauna due to

geographic isolation.• Historically used as a source of raw

materials for human settlements.