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THE BIOSPHERE. Objectives Define and explain the important terms Understand the main influences leading to plant and animal distributions Describe and explain the main characteristics of the major global biomes Explain some of the factors leading to change in these regions. Introduction.

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THE BIOSPHERE

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The biosphere l.jpg

THE BIOSPHERE

  • Objectives

    • Define and explain the important terms

    • Understand the main influences leading to plant and animal distributions

    • Describe and explain the main characteristics of the major global biomes

    • Explain some of the factors leading to change in these regions


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Introduction

  • The biosphere is the biologically inhabited portion of the Earth in which ecosystems operate

  • Studies of the biosphere are linked with geology, ecology, soils, atmospheric processes and climate, oceans

  • Humans influence the biosphere through a range of deliberate and inadvertent practices

  • Biomes are major global scale zones with characteristic life forms of plants and animals


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Figure 8.1


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Functions and processes within the biosphere: characteristics

  • The biosphere is characterized by its dynamism

  • Boundaries within the biosphere result from a range of factors

    • Often along environmental gradients

    • Often not a sudden change but transitional areas (ecotones)

  • Each region of the biosphere has distinctive energy flows, biomass, trophic levels, nutrient cycling


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Functions and processes within the biosphere: controlling factors

  • Temperature regime

    • Actual temperature and seasonal pattern is critical for life

    • Growing season creates a base-line of food for others

    • Adaptability to temperature ranges

  • Moisture availability

    • Local rainfall regime – esp. length of dry season

    • Potential evapotranspiration and accessibility to river/groundwater

  • Zonal factors

    • Regional macroclimate (equatorial, monsoonal etc) correlate to biomes

    • Creates favourable/unfavourable conditions for life

  • Azonal factors

    • Disrupt otherwise climatically-controlled pattern

    • Geomorphology affects drainage and aspect.

    • Geology


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Functions and processes controlling the biosphere: The major biogeographic realms

  • Biogeographical realms are divided into zones/biomes

  • Classification of realms

    • Holarctic (from Laurasia) – Palaearictic (Eurasia) and Nearctic (N America Greenland)

    • Palaeotropic (from Gondwanaland) – southern continents; Afrotropical, Indian, Indomalaysian , Neotropical, Australia, Antarctic realms

    • Usually ignores the oceanic realms

    • Classification helps in taxonomy

  • Past climatic and tectonic changes are vital to today’s patterns


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Figure 8.2


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TROPICAL BIOMES


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Figure 8.3


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Equatorial and tropical forests

  • Climate

    • mean annual temp ~25o with little seasonal variation

    • 2000mm rainfall/yr – dry season no longer than 5 months

    • Further from equator = increased seasonality

  • Soils

    • high rates of biogeochemical activity

    • Infertile soils, lack of recently weathered rock – oxisols

    • Fertility is dependent on continual leaf litter

    • Soil type changes with variability in seasonality

  • High net primary productivity

    • 40% global terrestrial productivity

    • Degree of seasonality has a large impact on primary productivit


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…cont

  • Rainforest vegetation

    • Broad leaved evergreens dominate in a closed canopy

    • Competition for light causes stratification of canopies and epiphytes and lianas (adaptive)

    • Distinctive tree types within each stratum

    • Adaptations for light, surplus water removal , phanerophytes

    • Characteristics between realms remain similar but actual species vary - e.g. dipterocarps (Indian) vs legumes (S American)

  • Rainforest animals

    • Animal species often restrict their range to a single stratum

    • Animal adaptations (prehensile tails, fruit eating birds)

    • Lack of under-storey vegetation allows space for large ground dwelling animals – wind pigs, jaguars, large rodents


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Figure 8.4

Source: From Schultz, 1995, after Leith, 1964


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Figure 8.5

Source: Photo courtesy of Sandra Patino


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Figure 8.6

Source:Jerry Young/Dorling Kindersley


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Figure 8.7

Source:Dorling Kindersley


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…cont

  • Regeneration

    • When natural clearings appear due to fire, wind or water species compete for the new niche (especially light)

    • Soil erosion and nutrient loss at a minimal

    • Mimicked by humans in shifting cultivation

  • Complexity

    • Associations of vegetation rather than domination by single species

    • High species diversity probably due to complex structure, length of time since major climatic disturbance

    • Local specific azonal factors cause high diversity – e.g. slope, local geology, drainage

    • Historical shifts between savanna and forest


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Savanna

  • Climate

    • Temperature is similar to rainforest but a longer dry season

    • Dr season = >250mm/month for > 5 months

  • Gradient from the equator

    • Savanna woodland → tree savanna → shrub savanna → savanna grassland

  • Soil = one of the major controls

    • Most found on continental shields – ancient infertile soil

  • Ecosystem change

    • Easily influenced by human activities and major climatic readjustment e.g. Quaternary


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Figure 8.10

Source: After Whittaker, 1975


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…cont

  • Vegetation

    • More open canopy than forests: few trees except near water table

    • Mosaic – diversity of structure due to differences in water and soil nutrients availability

    • ‘Fire season’ – allows fruiting and nutrient supply

    • Xeromorphic adaptations and Rhizomes

    • Grassland stands dominated by few species

  • Animals

    • Large numbers of herbivores (esp. Central and East Africa)

    • Large animal predators occupy wooded areas of shelter, preying on herbivores

    • Adaptations – nocturnalism to reduce water loss and migration to track seasonally available food


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Deserts

  • Climate = dominant control (hot and dry all yr)

    • Insufficient moisture for complete ground cover

    • Large diurnal temp fluctuations

    • Some areas = regular but insufficient rain to counteract evaporation

    • Some areas = no sporadic rainfall for years

  • Soils

    • Poorly developed but increased nutrients around roots

  • Basic ecology

    • Vegetation = varied but low in height and very open stands

    • Clustering dependent on water, local geology, geomorphology

    • Biomass is mainly underground – geophytes or therophytes

    • Low biodiversity

    • Net primary productivity is strongly related to rainfall


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Figure 8.12

Source:Photo courtesy of John Coleman


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…cont

  • Adaptations

    • Plant and animal adaptations to control evaporation and maximise water conservation (xeromorphic)

  • Plants adaptations

    • Control transpiration (nocturnal stomatal opening)

    • Woodiness prevents wilting

    • Lengthy dormant season

    • Annual plants – dependent on rainfall season

  • Animal adaptations

    • Physiological - surface area/body mass ratio, sweat control etc

    • Behavioural – nocturnal, dormancy, cryptozoic


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TEMPERATE BIOMES


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Figure 8.13


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Mediterranean/Chaparral Biome

  • Transition between desert and true temperate biomes

  • Climate

    • Warm all yr round with low rainfall, summer drought

  • Soil

    • Regardless of parent material the upper soil becomes very dry in summer – evaporites can develop

  • Vegetation

    • Tendency for xerophytic scrubland with strongly developed adaptations against natural fires

    • Thick, smooth bark, deep roots

    • Crytophytes – bulbs, rhizomes

    • Distinctive post-fire regeneration cycle exists

    • Animals adapt to avoid drought and fire stresses e.g. burrowing


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…cont

  • Mediterranean - once sclerophyllous mixed woodland - now dominated by maquis due to human impact

    • Scrubland, canopy may reach 3m (gorse, broom, olive etc)

    • Garrigue vegetation where less water (evergreen, more sparse)

  • Chaparral (N. America) - sclerophyllous

    • Thick bark, fore resistant (Eriodictyon tomentosum)

    • Deer, elk and grizzly bear

    • ‘soft chaparral’ near coast

  • S African Mediterranean has distinctive flora

    • Where temperate forest remains it is simpler than in the N Hemisphere

    • Southern Cape Province – coniferous Podocarpus understorey

  • Australia – mallee scrublands

    • Eucalyptus species with acacia understorey, marsupial grazers


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Figure 8.14


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Temperate grasslands

  • Continental interior of the Holarctic and eastern region of the Netropical

  • Climate – annual precn <500mm, long dry season

    • Continental convection rainfall in summer, snowfall in winter

  • Geomorphological and glacial heritage

    • Gently undulating areas with rich soils – agriculture e.g. US Prairies

  • Vegetation

    • Dominated by grasslands, usually perennial and xerophyllous

    • Adaptations to maximise effectiveness of precn and minimise fire damage

      • E.g. shallow, turf forming dense roots

  • Animals - originally large herds of herbivores

    • Lack of cover had caused development of speed, bulk or burrowing habits for protection

    • Reduced or extinct due to humans e.g. passenger pigeons of N America

  • Verv extensive human impacts


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Figure 8.16

Source: After Walter 1990


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Temperature deciduous forest

  • Only in N Hemisphere

  • Climate

    • Moist but temperate all yr, a few months above 10oC

  • Soils

    • Brown earth molisols – rich soil fauna and nutrients

    • Under conifers soils become leached – podzols – heathland results

  • Ecology

    • Mainly deciduous trees, some epiphytes

    • Four layers (canopy, shrub layer, field layer, ground layer) – dependent on species comprising the canopy

    • Very marked seasonality of vegetation - creates succession of dominants

    • Flowering trees and plants – assists wind pollination

    • Animals may hibernate and burrow to avoid winter effects

  • MASSIVE HUMAN IMPACTS– reduced coverage and species


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Figure 8.17

Source:Photo courtesy of Joseph Holden


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Southern hemisphere, evergreen temperate forest

  • Variant of temperate deciduous forest biome

    • S Hemisphere equivalent – later development of deciduous habitat in N Hemisphere after continental split

  • Ecology

    • Usually 2 tree canopies and a shrub layer

    • Climbers and epiphytes

    • Less frequently a ground flora

    • Southern Beech and podocarp family are important

    • Rich bird life exp New Zealand

      • e.g. meat eating parrots


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THE COLD BIOMES


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Figure 8.18


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Taiga

  • Lack of any extensive Taiga in the S Hemisphere

  • Climate

    • Cool all year and little rainfall (mostly continental interiors)

    • Extending poleward from < 5 months > 10oC to 1 month

    • Very limited growing season

  • Soil

    • Usually a podzol

    • Slow nutrient cycles, large accumulated litter layer, strong layering

    • Peat bogs develop where glacial effects impede soil drainage


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Taiga ecology

  • Wide ecotone between temperate and boreal forest mosaics

    • depends on local conditions e,g, soil type

  • Warmer and wetter taiga

    • unbroken forest stands

  • True central taiga

    • more discontinuous, greater dominance of ground layer – lichens

  • Dominant Species

    • Eurasian forests dominated by Norway spruce and Scots pine

    • American forest dominated by lodgepole pine and alpine fur

  • Adaptations - maximise growing season and utilise poor soils

    • increased stored sugar concentration in winter

    • fan shaped roots

  • Animals

    • Adapted to conditions e.g. migration, fur


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    Figure 8.19

    Source: Photo courtesy of Ed Reschke/Peter Arnold Inc/Still Pictures


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    Tundra

    • Most challenging environments for plants and animals

    • Climate

      • Equator limit = 10oC for the warmest month

      • Winter may plunge to -50oC

      • Strong, dry, cold winds prevalent, snow accumulates

      • Lowland areas characterised by continuous permafrost

      • Warmer in coastal regions

    • Soils (cryosols)

      • Litter layer of partly decomposed, highly acidic plant matter

      • Gleyed horizon overlies permanently frozen layer

    • Geomorphology– very strong immediate influence

      • Glacial erosion and current fluvial activity caused shallow soils

      • Underlying sands and gravels left in valley floors – causes veg mosaic


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    Figure 8.20


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    Figure 8.21


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    …cont

    • Vegetation

      • Limited floristically because Quaternary destroyed the biome

      • 3 fold structure –low shrub, tussocky grasses, mosses/ lichens

      • Becomes more simple the more extreme the conditions

      • Slow growth

      • Most are perrenial

      • Adapted to reproduction in very short growing season e.g. bulbs

      • Grasses and sedges dominate and dwarf trees e.g. Betula nana

      • Health dominates on coarser substrate – Erica families

    • Animals

      • Migrating animals – causes interesting population dynamics

      • Low productivity requires large areas to support migrating herds e,g, reindeer

      • Hibernation, burrowing an insulating fur/feathers

    • Convergent evolution – very similar habit and structure across all realms


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    Mountain biomes

    • Topography plays a local role in altering regional biome patterns

    • Mountains form barriers to dispersal of life forms

    • Mountains often have unique biome characteristics and gradients

      • Aspect - impacts on local scale biodiversity

      • Local land use patterns change in mountain areas

    • Case study – Andes mountain biome

      • Lower slope = tierra templada

        • tropical pre-mountain forest

      • Middle slopes – upper tierra templada/lower tierra fria

        • temperate rain or cloud forest

      • Upper slopes = Tierra fria and tierra helada

        • above treeline species are xerophytic with giant forms of plants due to reduced oxygen and increased UV radiation


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    Figure 8.22

    Source: After Breckle, 2002


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    Figure 8.23

    Source: Photo courtesy of Julia Edwards


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    Changing biomes

    • Despite specific characteristics (functional or structural) – all biomes are very dynamic in nature

    • Natural changes have always occurred however human intervention is now increasingly important

      • anthropogenic climate change

      • intensified resource utilisation

      • Introductions of alien species – altering local balances

    • Approaches to resource utilisation are changing – as reflected in the popularity of venues such as the Eden project

    • Ho resilient is the biosphere in response to human and natural agents of change?

      • History suggests a large capacity to accommodate vast climatic changes

      • However gaps exist in our knowledge

      • Need management


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    Figure 8.24

    Source: After Whittaker, 1975


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    Summary

    • Themes for drawing geographical comparisons between biomes

      • Climate, soil, wildlife types, adaptations

      • Local human factors also alter biomes

    • Ecotones

    • Tropical biomes - forests, savanna, desert

    • Temperature biomes – forest, grasslands

    • Cold biomes – taiga, tundra


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