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Ecosystems and sustainability in a changing world > L2 > Flashcards

L2 Flashcards

1
Q

Biome definition

A

Areas of vegetation characterised by the same plant life forms

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2
Q

How are Biomes classified?

A

Classification of terrestrial ecosystems using their structure

Eg what grows there

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3
Q

Differences in vegetation in Biomes?

A
  • Trees vs shrubs vs grasses
  • Evergreen vs deciduous
  • Broadleaf (angiosperm) vs Needleleaf (coniferous)
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4
Q

4 Tree life forms

A

Coniferous or angiosperm

Evergreen vs deciduous

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5
Q

Evergreen

A

Carry a leaf canopy the whole year round

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6
Q

Deciduous

A

Leafless some parts of the year

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7
Q

2 Ways of Biome differentiation?

A

Temperature

Water availability (more tropics specific)

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8
Q

Higher northern latitude Biome features…?

A

More evergreen

More coniferous

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9
Q

Southern latitude Biome features…?

A

Southern trees often winter deciduous

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10
Q

What are the two responses trees can drop their leaves to?

A

Temperature

Water availability

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11
Q

Relationships of Biomes with global climate

A
  • Areas of the world with similar climate support vegetation with similar life forms
  • At higher latitudes the temperature at a same point at a mountain is at a lower elevation
  • Biomes change with altitude
  • Results in altitudinal tree bands at lower altitudes
  • Same temperature conditions but at different altitudes depending on latitude
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12
Q

Similar climate supports…?

A

Vegetation with similar life forms

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13
Q

Biomes change with…?

A

Altitude

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14
Q

Humboldt’s legacy - Eurocentric, climate- centered perspectives on biome distributions

A

Climate determines vegetation and thus determines biome distributions

Climate can be looked up and the biome can be calculated from known tables etc eg life zones

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15
Q

Two rules for biome distributions (life forms can be predicted off these two rules)

A

Environmental filters

Competition

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16
Q

Environmental filters (biomes)

A

Survival of cold or dry environmental extremes requires specialist adaptations

  • These can be a trade-off
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17
Q

Competition (Biomes)

A

Specialists are excluded from warmer and/or wetter environments by stronger competitors

  • Not having to tolerate extremities means these plants are less fit compared to competitors
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18
Q

Low temperatures exclude cold- sensitive plants

A

Eg tropical and sub-tropical plants

  • Chilling injuries <10-12C
  • Bananas and mangos are chilling sensitive
  • Freezing injury and death <0C
  • Avocado and palm
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19
Q

The three mechanisms of freezing resistance

A

Metabolic costs

Structural adaptations

Hypothesised trade-off between climate resistance and growth

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20
Q

Metabolic costs

A

Accumulate solutes which depress freezing point of tissues

Anti-freeze protein synthesis

Resource allocation competes with growth

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21
Q

Structural adaptations

A

Eg thick walled cells

Narrow xylem vessels to resist freezing injury

Lower rates of resource capture and growth (photosynthesis)

22
Q

Trade-off between freezing resistance and growth rate

A
  • In hot climates plants with adaptations to resist freezing grow slower
  • Trade-off apparent
23
Q

What two factors act as filters?

A

Freezing and drought

24
Q

Freezing and drought act as filters

A

-Opposing forces from warm to cold and wet to dry

  • Factors exclude species that don’t have adaptation to deal with them
  • Competitive exclusion, species that lack adaptations but are competitive outcompete specialists in warmer and wetter environments
  • Cold or dry adapted species are excluded from warmer, wetter climates by competition
25
Q

Competitive exclusion

A
  • Species that lack adaptations but are competitive outcompete specialists
  • Cold or dry species are excluded from warmer, wetter climates by competition
26
Q

Humboldt Review

A
  • Roles of climate and soils in determining biome distributions
  • Emphasis on forests as potential and most important vegetation
  • View of open landscapes as being degraded by fires and deforestation
  • Lead to ideas that open landscapes being degraded landscapes?
27
Q

The tropical savanna Biome

A
  • Tree-grass coexistence
  • Continuous ground layer of grasses and varying tree cover
  • Grasses are C4 as in hot environments
28
Q

Deforestation and fires in tropical forests:

A
  • Deforestation and fires in tropical forests can lead to savanna-like vegetation
  • Often referred to as ‘savannisation’
  • This looks like savanna according to its definition but is not
29
Q

Does savannisation result in actual savanna?

A

No it looks like savanna but is not

30
Q

Savannas are often portrayed as…?

A

Degraded ecosystems

31
Q

Savannas are often portrayed as degraded ecosystems

A
  • Widespread perception that savannas are unnatural, arising from deforestation and fires lit by people
  • PROBLEM - large areas of savanna are targeted for restoration programmes for degraded land
32
Q

Savanna grass communities in Madagascar are adapted to fire or grazing and are rich in endemic species

A
  • Many grass flora are adapted
  • Grazing- adapted species evolved in response to now-extinct megafauna
  • Grazing-adapted communities are today maintained by domestic cattle
  • We can work out fire adapted/ grazing adapted savannas based on characteristics of plants growing
33
Q

How can we work out fire adapted/ grazing adapted Savannas?

A

Based on the characteristics of plants growing there

34
Q

In ancient savanna what decides tree density/

A

Fire and herbivory

35
Q

What are the two processes that maintain the ancient savanna Biome

A

Fire and herbivory

36
Q

What is the escape height?

A

The tree must reach a set height to survive fires

37
Q

What is the escape height determined by?

A

Frequency of fires and rate of tree growth

38
Q

What is browse height?

A

Protection from herbivores

If animals can reach growing tips they can stop tree growth

39
Q

Diversity of savanna ecosystems?

A
  • Previous ecosystems characterised as forest can be defined as savannas based off the functional definition
  • Even savannas with high tree cover have dense ground cover and fire adapted trees
  • They all have a deep layer for continuous grasses and fire adapted trees
40
Q

How are savanna mosaics maintained?

A

By fire-promoting grasses and fire-tolerant trees

41
Q

How are forest mosaics maintained?

A
  • Forests maintained by shading which excludes shade intolerant grasses
  • Forests have no light for grass to establish so no fuel for fire
42
Q

Mosaics of grassy and forest vegetation

A
  • Not climatically determined
  • Sharp boundaries between savanna and forest
    • Savannas are maintained by fire-promoting grasses and fire-tolerant trees
  • Forests maintained by shading which excludes shade intolerant grasses
  • Forests have no light for grass to establish so no fuel for fire
    • Forests and savannas coexist in the same climate, with abrupt transitions
43
Q

Misclassification of Asian savannas

A
  • Long history of savanna use and management (old vegetation types)
  • When colonisers came and saw mosaics they presumed these were degraded ecosystems so planted trees
  • In reality this is misclassification and leads to miss management
  • Fire and grazing suppression in ‘dry forests’
  • Leads to elimination of fire tolerant vegetation and forest establishment
44
Q

Outcomes of misclassification of Asian savannas?

A
  • Fire and grazing suppression in ‘dry forests’
  • Leads to elimination of fire tolerant vegetation and forest establishment
45
Q

Rising CO2 promotes growth of…?

A

Savanna trees

Tree growth and root storage depends on atmospheric CO2

Trees escape fire at high CO2, therefore reach escape height quicker, therefore reaching higher tree density

46
Q

Climate change impacts in savannas

A

Rising CO2 promotes growth of savanna trees

  • Savanna trees are C3
  • Grasses in savannas are C4
  • Tree growth and root storage depends on atmospheric CO2,
  • Trees escape fire at high CO2, therefore reach escape height quicker, therefore reaching higher tree density
  • Rising CO2 benefits C3 trees more than C4 savanna grasses
  • Promotes growth of trees over grasses
47
Q

Climate change promotes… in savannas?

A

Growth of trees over grasses

48
Q

Consequences of climate change on Savanna:

A
  • Woody plant encroachment into savannas
  • Open savanna is covered in greater tree cover compared to less CO2
  • Woody plants deplete savanna groundwater and threaten soil carbon stocks
49
Q

Woody plant densities impact livelihoods

A
  • Less pasture for grazing domestic animals
  • Some charismatic animals require open landscapes
  • Firewood harvesting and charcoal production
  • Trees are often spiky and sharp, this is not good for cattle
  • Land cannot therefore be used for grazing
50
Q

Degradation arises through opposing processes in forests and savannas

A
  • Tropical forests are rich everywhere
  • Tree removal doesn’t suddenly result in rich ground flora
  • In an open savanna tree there is poor canopy diversity etc however ground flora is diverse
  • When savanna is encroached/ planted, diversity of ground layer is reduced and replaced with species poor trees etc
  • If tall trees grow or invade, this grassy layer is then competitively excluded to form a species poor canopy
51
Q

In an open savanna is there more or less canopy diversity than forest?

A

Less

52
Q

Conclusions:

A
  • Fires and herbivores have ancient roles in maintaining savannas
  • Tree encroachment or planting in savannas degrades ecosystem functions and services
  • Colonial misclassification of these ecosystems led to mismanagement

Ecosystems and sustainability in a changing world (21 decks)

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