Lecture 15 The Biosphere and Biomes of the Earth

Biosphere

• part of the Earth system that includes all living things, including plants, animals, and other organisms

  • zone of life on Earth, integrating all living beings and their relationships

  • a part self-regulating system with input from the sun, cosmic radiation and heat from the interior of the Earth

Vladimir Vernadsky 1926

• argued that the makeup of the atmosphere was strongly influenced by life

• global sum of all ecosystems

• living organisms could reshape the planet just as strongly as any physical force

Basic Drivers of Climate

• sunlight intensity

  • affects, temperature, winds, precipitation, ocean circulation

• tropics are the origins of global atmospheric circulation

Biome

• an intercontinental formation of similar climate and vegetation, organises large-scale ecological variation

  • characteristic animal and plant adaptations

• at its most basic, temperature vs precipitation graph

Why What is Where

• not only determined by climate

• soils: e.g. nutrients, texture

• species: e.g. physiology, ecology

• history and chance: e.g. fire, volcano, humans

• classify the biosphere to identify key properties so:

  • we can identify and analyse causes of change

  • we can predict change

Global Distribution of Biomes

• latitude, continentality, etc.

• more diversity in tropics

Tropical Forest

• consistently high temperature during the year

• mean annual temp in coldest months >18C

• difference of <5C from coldest to warmest month

• diurnal climate, large shifts from day to night

• common where every month has precipitation of >100mm, with only short dry period

• tall growing forests with closed canopies

Savannah

• transition from a humid to semi-humid climates

• longer dry periods, longer still at higher latitudes

• vary in terms of vegetation

• 400-1500mm per annum

• 18-25C mean annual temp

• cover ~20% of the Earth’s landmass

Desert

• ~20% of Earth’s land surface

• generally less than 250mm per year

• generally between 15-30 degrees N and S

• very slow soil development, e.g. lithosols or syrosemes

• microbial crust formation

• 20-25C mean annual temp

• massive day-to-night temperature variation

Grasslands

• grasses 20% of species but 90% of biomass

• continental, colder and drier than similar coastal latitudes

Temperate Deciduous Forest

• less rainfall than tropics, but less atmospheric demand

• 500-2500 mm per year

• 10-15C mean annual temp

Boreal Forest

• lower temps, strong seasonality

• 500-1500mm/year

• 5-15C during vegetation season

• areas of permafrost, impacting carbon storage, root access, water availability

• shifting active layer

Tundra and Polar Desert

• 50-2000mm/year

• only just above 0C during growing period

• impacts of physical processes, e.g. freeze-thaw

  • patterned soils, polygon soils

• lichens and grasses

Antarctica

• size: 11,900,000km2 contiguous continent

• lowest recorded temperature: -89.2C

• average height: 2,500m

• highest recorded wind speed: 527 km/h

• approx 80% of the world’s freshwater is frozen in Antarctica