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world vegetation > exam 2 > Flashcards

exam 2 Flashcards

1
Q

savanna geographic distribution

A
  • ecosystems which lie between forests and deserts of tropical regions
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2
Q

Savanna vegetation (broad)

A
  • vegetation is a mix of trees and grass (co-dominant)
  • continuous grass layer
  • discontinuous tree/shrub layer
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3
Q

savanna major areas- AFRICA

A
  • miombo woodland; trees
  • bushveld; thorny
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4
Q

savanna major areas-BRAZIL

A
  • campos: few trees
    -llanos; few trees
    -caatinga; thorn shrubs
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5
Q

savanna major areas-S. AMERICA

A
  • cerrado; densely wooded
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6
Q

savanna major areas-AUSTRALIA

A
  • mulga; acacias and eucalypts
    -brigalow; acacias and eucalypts
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7
Q

savanna climate (broad)

A
  • strictly seasonal; usually summer rain
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8
Q

savanna temperature

A
  • mean mostly temperature is >18 C
  • max temps are at end of wet season
  • much variation (4-30 C)
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9
Q

savanna rainfall

A
  • <1500 per year, but >250 mm per year
  • dry season of several months
  • <25 mm per month in dry season (africa, asia, and australia)
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10
Q

savanna climate and physiognomy

A

diverse climate= diverse physiognomy
- high rainfall = more tree cover

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11
Q

savanna woodland

A

deciduous and semi-deciduous woodland of tall trees (>8 m high) and tall mesophytic grasses (>80 cm high); spacing of the trees more than the diameter of the canopy

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12
Q

savanna parkland

A

tall mesophytic grassland (grasses 40-80 cm high) with scattered deciduous trees (<8 m high)

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13
Q

savanna grassland

A

tall tropical grasslands without trees or shrubs

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14
Q

low tree and shrub savanna

A

communities of widely spaced low-growing perennial grasses (<80 cm high) with abundant annuals and studded with widely spaced, low-growing trees and shrubs (ofter < 2 m high)

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15
Q

thicket and shrub savanna

A

communities of trees and shrubs with out stratification

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16
Q

origins of savannas - climate ?

A

climate alone cannot explain as closed canopies and open savanna occur under the same climatic conditions

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17
Q

relict or refuge hypothesis

A
  • savanna vegetation is +- 25 million years old
  • relict of a more widespread dry vegetation type of the glacial Pleistocene
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18
Q

major factors determining savannas

A

(1) water ; “hydrological hypothesis” - seasonal rainfall, flooding, excessive drainage
(2) mineral nutrients ; “edaphic hypothesis” - grasses increase as soil fertility decreases
(3) fire ; “anthropogenic hypothesis” - reduced tree cover
(4) herbivory

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19
Q

characteristic life forms

A

(1) trees; phanerophytes
(2) grasses; hemicryptophytes
(3) woody succulents/ caudiciforms; chamaephytes, cryptophytes
(4) succulents
(5) forms/annuals ; therophytes

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20
Q

distribution of life forms of tropical forests v. savannas

A

tropical forests; high occurrence of phanerophytes with low numbers of other forms.NO therophytes

savannas; more distributed occurrence of life forms with a good amount of phanerophytes, chamaeohytes, hydrophytes, and thereophytes

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21
Q

adaptation of grasses in savannas

A

(1) rhizomatous
(2) adventitious roots
(3) scleromorphic leaves
(4) many C4 species

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22
Q

C4 adaptation of savanna grasses

A
  • C4 is of advantage in high temperatures and high light intensity
  • uses less water than C3
  • does not respond to increased CO2 in the atmosphere
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23
Q

C4 mechanism in grasses

A
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24
Q

adaptation of trees in savannas

A
  • large root: shoot ratio
  • enlarged subterranean roots
    -caudiciforms and bottle trees (fat or swollen trunks)
  • deciduousness
  • thick cuticles, sunken stomata (reduce water loss)
  • small leaves, sometimes sclerophyllous
  • thick bark
  • coppicing (cut at base and allowed to regrow for a sustainable supply of wood)
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25
Q

why do savanna trees have flat tops?

A

fire protection
- browse height v escape height

No need for savanna trees to grow super tall and horizontal growth is enough to gather sufficient light no

Horizontal growth protects central branches from grazing

Help trees to resist drying winds

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26
Q

savanna phenology

A
  • savanna plants are not synchronous
  • flowering
    • (late dry season) into rainy season
    • temperature and day length trigger response
  • leaf shedding
    • dry period (dependent on reserves)
    • may be facultative deciduous
      -annuals
    • wet season or dry season
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27
Q

Succession- savanna fires areas of occurrence

A

Grassland savannas
-continuous grass cover
- fuel load of > 1 t h -1

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28
Q

Succession- savanna fires area where fires do not occur

A
  • semi-deserts
  • thorn savannas (bushveld)
  • seasons of above average rainfall
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29
Q

savanna fires - causes

A

(1) lighting
(2) humans; to maintain and improve pastures, clear land and increase fertility, keep wild animals away, eradicate vermin (snakes)

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30
Q

savanna fires - characteristics

A

-dry season
-frequency; 1-30 years apart (rainfall, grazing)
- type; surface fires, tree layer affected by the intensity of the fire
- intensity; 100-5000 kWm-1 , dependent on fuel load (amount, type, water) and climatic conditions

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31
Q

Vegetation type and fire characteristics; Grasslands

A

Frequency; annual or longer, depending on grazing pressure and rainfall which determine fuel load

Season of fires; fires occur in the fry season when grasses are dormant

Intensity of fires; fire intensities range from <100 - >5000 kWm-1

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32
Q

Vegetation type and fire characteristics; African savannas

A

Frequency; range from annual to once every 30 years or more, depending on rainfall and grazing pressure

Season of fires; fires occur in dry seasons when grasses are dormant

Intensity of fires; as for grasslands

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33
Q

savanna fuel characteristics and types of fires

A
  • fuel characteristics; fine grass litter and live grass. trees not normally considered part of the fuel complex
  • types of fires; surface fires, tree layer affected by intensity of surface fire
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34
Q

savanna fires; consequences –reduction of above group phytomass

A

reduction of above group phytomass
- normal reduction levels; grass and grade litter 70-90%, tree litter 20-50%, twigs bark and woody parts 20%, standing dead trees 20%
- reduction in humus not significant
- soil flora, fauna and below ground organs survive
- fire temperature (and hence plant survival) differs with heigh above ground
- as fire fronts move relatively rapidly high temperatures are experienced for a few seconds only
- soil under fallen trees often hotter as they have more intense heating

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35
Q

savanna fires; consequences –effects on soil

A

(1) heat budget; increased abosportion of solar radiation accelerates drying and humus breakdown
(2) water budget; high evaporation equals lowers rainfall penetration
(3) susceptibility to erosion: unprotected, lowered permeability leads to sheet wash
(4) supply of mineral nutrients; high availability to plants of K, Ca, and Mg. N,S, P volatilize. removed by wind and water

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36
Q

savanna fires; consequences –trees, effects and responses

A

dependent on species, age and fire intensity
- most very small and very tall trees survive
-regenerate by coppicing from tree stump or suckering from roots
- early season fires often set to protect trees (see slide 12 on savanna 2)

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37
Q

savanna fires; consequences – grasses, effects and responses

A
  • most above ground phytomass removed
  • a growth flush follows fire even without rain
  • growth triggered by fire (heat shock, smoke– butinolide, active butenolide in smoke stimulates germination and seedling growth)
  • post-burn conditions favor growth (higher light, temperature and nutrients)
  • early season fires disadvantageous, disrupts relocation of nutrients to roots
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38
Q

Grass/Tree interactions: the “Gulliver Effect”

A

Savanna trees and grasses are connected through the effects of fire and herbivores
-“gullivers”: plants which dominate communities as adults but which struggle to emerge from the herbaceous layer as juveniles
The herbaceous layer (grasses) interferes with Gulliver recruitment by
(1) suppressing seedlings
(2) slowing the growth of established plants
(3) fuelling frequent fires which stunt/kill survivors

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39
Q

Factors promoting Gulliver suppression –> Grasslands

A
  • frequent fires
  • browsing animals (elephants, porcupines, etc)
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40
Q

Factors promoting Gulliver release –> Woodlands

A
  • fire suppression
  • reduction in fuel load –> grazing, drought (increase in fire intervals)
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41
Q

savanna fires; consequences – community structure

A

fire produces a large scale patchwork/mosaic of areas at different stages of succession –> fire climax formation

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42
Q

Savanna productivity

A

intermediate between tropical forests and deserts. variable, affected by rainfall (amount, season) and burning

43
Q

savanna nutrient cycling

A

soil nutrient supply is low, thus plants optimize use by:
(1) high roots: shoot ratios
(2) intensive root systems
(3) N2 fixing symbionts and mycorrhizae
(4) Nutrient translocation from old to young leaves

44
Q

dung beetle

A

important in rapid decomposition of dead organic materials. dung beetles research on if they use the stars as a gps

45
Q

termites

A

characteristic of all savannas
- above ground termitaria for some species –> termitaria savanna
- termites live exclusively on dead organic material, digest cellulose
- process +- 50% of material in savannas
- density increases with amount of organic material

46
Q

Plant herbivore interactions; adaptations which reduce herbivory STRUCTURAL DEFENSE

A

grasses - location of meristem , silica cells , and hairs
trees - thorns, affects bite size `

47
Q

Plant herbivore interactions; adaptations which reduce herbivory CHEMICAL DEFENSE

A

grasses- selected for/against based on content of ; fiber, protein, sodium

trees- palatability correlates with digestibility, protein versus tannin (deterrents as they reduce nutrient uptake and may have consequences in the midgut) content. secondary compounds such as saponins modify response, food choice innate and learned
- some species extremely toxic

48
Q

Plant herbivore interactions; adaptations which reduce herbivory RESOURCE PARTITIONING

A

geographic separation

habitat separation

niche separation
i. sympatric browsers
- differing browsing heights
- differing tolerance to plant chemicals
- differing requirements in terms of quality of food
ii. sympatric grazers
- grazers do not separate on the basis of different plant chemicals, thus much of niche portioning is related to size and digestion
- fine grazers versus coarse grazers is dependent on mouthpart size
-digestion efficiency greater in bovids (foregut fermentation) than equids (hindgut fermentation)

49
Q

Plant herbivore interactions; adaptations which reduce herbivory SEASONAL MIGRATIONS

A

Serengeti- Masai Mara
- biomass and protein content decline throughout the growth season
- as food supples decrease start moving into the long grass areas
- buffalo and zebra first, wildebeest next
- migration order determined by size and selectivity

50
Q

threats to savannas

A

(1) global climate change
(2) bush encroachment
(3) desertification

51
Q

global climate change

A

“CO2 fertilization effect”
- recent studies show that many of the world’s savannas, including famed southern African landscapes, are experiencing significant change as rising levels of carbon dioxide in the atmosphere favor the growth of trees over grasslands
- “savannas are the result of a battle for living space between grasses and trees that neither side has won”

52
Q

bush encroachment

A

Woody plant encroachment is a natural phenomenon characterised by the increase in density of woody plants, bushes and shrubs, at the expense of the herbaceous layer, grasses and forbs

local drivers
- addition of grazers and removal of browsers
- reduction of mega faunal densities
- fire management
- fencing of areas, provisioning of water (sedentary game)

global drivers
- increased rainfall volume
-increased rainfall intensity
- elevated CO2 levels (improved WUE)

in bush encroachment, often trees give way to shrub

53
Q

desertification

A
  • the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture
  • irreversible decrease in productivity (change in vegetation) of arid lands
54
Q

causes of desertification– irrigated croplands

A
  • irrigated croplands, whose soils are often degraded by the accumulation of salts
  • evapotranspiration results in salt accumulation in surface soils
  • in the US, salt accumulation has lowered crop yields across more than 50,000 square km, an area that is about a quarter of the country’s irrigated land
55
Q

causes of desertification– rain fed croplands

A
  • rain fed croplands, which experience unreliable rainfall and wind driven soil erosion
  • crops grown are annuals
  • previously grasslands (mix of annuals and perennials) with 250-500 mm annual rainfall
  • rainfall varies year to year
  • crop failure common in drought years
  • wind erosion and abandonment of land (1% per year)
56
Q

causes of desertification– grazing lands

A

-grazing lands, which are harmed by overgrazing, soil compaction, and erosion
- trampling destroys plants including plant roots that bind soil
- soil erosion when it rains
- reduce plant communities and alter the species composition

57
Q

causes of desertification–overconsumption of fuelwood

A

-overconsumption of fuelwood in dry woodlands
- in Africa and Asia wood is the principle fuel for heating and cooking
- often converted into charcoal as charcoal produces less smoke
- inefficient, up to 75% of the energy potential is lost

58
Q

causes of desertification– increased sedentary population

A

-increased population and livestock pressure on marginal lands

59
Q

causes of desertification–climate change

A
  • more rapid with desertification
  • more variation in climate increases desertification potential
  • hotter and drier conditions make desertification more likely
60
Q

solutions to desertification

A

large scale:
- economic and technical measurements to reduce global warming
- social and economic measures that support nomadic cultures

local scale:
- salt traps
- covers crops and crop rotation
- rotational grazing
- terracing, wind breaks, dune stabilization

61
Q

arid

A

excessively dry; insufficient rainfall

62
Q

tropical forests productivity

A

productivity: rate of accumulation of energy or biomass

high for tropical rainforests because of: light, water, mesic temperatures, low seasonality

63
Q

nutrient cycling

A

the basics
- nutrients cycle between abiotic and biotic compartments
- compartments may act as reservoirs
- rate of nutrient cycling (not reservoir size) most important in determining plant productivity
- “efficient cycles have low outputs”

64
Q

tropical forests nutrient cycling

A

(1) soils; poor, low nutrient status
(2) most nutrients in plants and recently dead organic matter

1 and 2 –> plants are recapturing dissolved minerals as they are released during decomposition (rapid with agents termites, bacteria, and fungi)

65
Q

tropical forests; replenishment of soil nutrients from…

A

(1) weathering of parent rock
(2) atmosphere

VERY LOW AMOUNTS AND SLOW

ex. ancient african fish dust nourishes Amazon
- dust blown from the sahara to the amazon contains essential nutrients
- phosphorus in the dust is derived from the bones and sea;es of fish and other organisms that lived in Megalake Chad, thousands of years ago
- fish phosphorous more soluble than that from rocks

66
Q

mechanisms that enhance nutrient uptake

A

(1) mycorrhizae
(2) surface roots
(3) sclerophylly

67
Q

tropical rain forests show fragility to …

A

(1) clearing
(2) slash and burn
(3) logging

68
Q

deserts- geographic distribution

A

20% of acid areas are covered by sand
- 2% in North America
- 45% in Central Asia
- 28% in Saharan

69
Q

defining a desert

A

(1) climate aridity
(2) moisture-dependent site conditions
- plants grow ,<5 months per year
- water stress occurs even during the rainy season
- vegetation patchy and xerophytic (plant that has adaptations to survive in an environment with little liquid water)
- drainage into sinks, rivers often dry

70
Q

types of desert

A

Sub-tropical – 30 N & S Sahara

Cool coastal– cold currents Namibia (Benguela)
Atacama (Humboldt)
Baja (California)

Rainshadow Mojave
Great Basin
Patagonia
Great Australian

Continental interior Australian
Gobi

71
Q

desert precipitation

A

low
semi arid: 150 to 250-500 mm y
arid: 60 - 100 to 150 - 250 mm y
extremely arid: 60 - 100 mm y

variable throughout the year

pattern of variation unpredictable

72
Q

desert temperature

A

-reflects geographic position 4 - 40 C
- at extremes, temperature can control plant growth

73
Q

desert soils – salinity

A
  • ascending water: high calcium carbonate and higher pH to alkaline (basic or greater than 7)
  • evaporation concentrates salts
74
Q

desert soils – desert pavement

A

-surface of angular, interlocking fragments of pebbles, gravel, or boulders in arid areas.

75
Q

desert soils – water

A
  • soil is the major water reservoir
  • soil water is spatially heterogenous
  • soil water content is affected by ..
    precipitation: runoff
    redistribution
    retention
    plant spacing
    animal activity
76
Q

climate variability v heterogeneity

A

climate variability emphasizes temporal variability of water input

heterogeneity emphasizes spatial variability of water availability

77
Q

species diversity

A

decreases with increasing environmental stress

tropical forest > savanna > desert

78
Q

desert growth form diversity

A

-high
- reflects spatial and temporal (relating to time) heterogeneity (diversity) of the water supply
- reduces competition for a limiting resource

79
Q

desert – adaptations of plants to arid environments

A
  • adaptations reflect the impact of water stress on carbon economy
  • different strategies have different survival values versus growth potential
80
Q

survival strategies – drought escaping

A

ephemerals (a plant that grows, flowers, and dies in a few days)
therophytes (annual plants that complete their life cycle in a short period when conditions are favourable and survive harsh conditions as seeds)
annuals
opportunistic

81
Q

survival strategies – drought avoiding

A

(1) water spenders
- high water uptake
- high growth rates
(2) water savers
- reduced water loss
- high survival

82
Q

survival strategies – drought tolerating

A

(1) dehydration avoiding
(2) dehydration tolerating

loose water during drought
partial —–> total
protoplasmic dehydration

survival under extreme drought

83
Q

drought escape : therophytes

A
  • annuals complete their lifecycle in < 8 weeks
  • rainfall triggers germination
  • germination is rapid , 1 h
  • life cycle is rapid
84
Q

drought escape : therophytes – show phenological/ phenotype plasticity

A
  • greater seed set in wet years
  • facultative selfing if pollinator not present
  • germination over a broad range of temperatures in some species
  • temperature specific niche separation
85
Q

drought escape : therophytes – seed banks

A
  • soil
  • surface
  • variable densities
  • lowest in washes
  • distribution altered by foraging ants
  • foraging decreases densities BUT provides germination sites (ants) and seeding competition
86
Q

drought escape : therophytes – safety mechanisms

A

HETEROBLASTY
- two types of seeds that differ in their level of dormancy

+- 6 seeds
1 immediate germination
1 after 1 year
others after several years

germination spread in time

87
Q

amphicarpy

A
  • two distinctly different fruits

1st survival: subterranean
- larger
-not dispersed
- more drought tolerant
- moisture penetrates along root channels

2nd dispersal: aerial
- smaller
-wind dispersal
-do not develop in dry years

88
Q

Mycorrhizae

A

A symbiotic association between plant roots and fungi. Their major role is to enhance nutrient and water uptake by the host plant by exploiting a larger volume of soil than roots alone can do.

89
Q

Surface roots

A

Roots grow towards the surface to access sufficient oxygen and nutrients that may be lacking in the soil.

90
Q

Sclerophyll

A

Type of vegetation characterized by hard, leathery, evergreen foliage that is specially adapted to prevent moisture loss. Adapted to long periods of dryness and heat.

91
Q

Slash and burn

A

Slash and burn agriculture is a widely used method of growing food in which wild or forested land is clear cut and any remaining vegetation burned. The resulting layer of ash provides the newly cleared land with a nutrient rich layer to help fertilize crops.

92
Q

Give the reasons crop yields decline rapidly when crops such as corn are planted in areas cleared of tropical forests.

A

Soils in tropical forests are poor with low nutrient status to begin with and plants depend on nutrient cycling (recently dead organic matter- recapture dissolved minerals that are released during decomposition) in order to obtain the nutrients needed for survival. Replenishment of soil nutrients can come from the weathering of parent rock and the atmosphere but this is a very slow process with little payoff. Tropical rainforests are easily damaged by clearing due to nutrient lacking/infertile soil that needs inputs from diverse plants in order for nutrient cycling to take place. Removal of trees and layers that usually characterize tropical forests also disrupt the ecosystem, weather patterns, light availability, etc.

93
Q

Even if farmers in the tropics have enough free capital to purchase fertilizer, this is probably not a good solution. Why?

A

Fertilizers in the long run can actually be harmful to the environment due to water pollution and soil degradation. They do provide nutrients in the short term but setting up an actual nutrient cycle is more sustainable. They also still do not solve the problem of inadequate shade and protection from erosion.

94
Q

Ideas for good solutions? (Nutrient cycling Q)

A

Planting other plants alongside the crop that are characteristic of tropical forests, such as trees, can aid the growth of the intended crop. It can provide shade for excessive sunlight or rain and increase input for nutrient cycling. Crop rotation is also important in conserving soil fertility and nutrient availability, which is seen in the rotation of the rice, corn, and beans.

95
Q

Deciduous

A

Shedding its leaves annually

96
Q

Phanerophytes

A

Buds on exposed branch tips:trees

97
Q

Chamaephytes

A

Buds close to the ground, protected by snow

98
Q

Hemicryptophytes

A

Buds at soil level, protected by dieback

99
Q

Cryptophytes

A

Bulbs, rhizomes, corms, etc., protected by soil

100
Q

Therophytes

A

Seeds

101
Q

Rhizomatous (grass adaptation)

A

Horizontal form of plant stem that grows underground which can form roots and shoots that grow into a new plant

102
Q

Adventitious roots

A

Plant roots that form from any non root tissue in response to stress conditions such as flooding, nutrient deprivation and wounding

103
Q

Scleromorphic leaves

A

Firm and stiff leaves with thickened epidermis and cuticula but with mechanisms to promote water transport under beneficial conditions

104
Q

productivity of savanna

A

mean 900. less than tropical rain forests but more than woodlands and grasslands.

world vegetation (4 decks)

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