exam 2 Flashcards
(104 cards)
1
Q
savanna geographic distribution
A
- ecosystems which lie between forests and deserts of tropical regions
2
Q
Savanna vegetation (broad)
A
- vegetation is a mix of trees and grass (co-dominant)
- continuous grass layer
- discontinuous tree/shrub layer
3
Q
savanna major areas- AFRICA
A
- miombo woodland; trees
- bushveld; thorny
4
Q
savanna major areas-BRAZIL
A
- campos: few trees
-llanos; few trees
-caatinga; thorn shrubs
5
Q
savanna major areas-S. AMERICA
A
- cerrado; densely wooded
6
Q
savanna major areas-AUSTRALIA
A
- mulga; acacias and eucalypts
-brigalow; acacias and eucalypts
7
Q
savanna climate (broad)
A
- strictly seasonal; usually summer rain
8
Q
savanna temperature
A
- mean mostly temperature is >18 C
- max temps are at end of wet season
- much variation (4-30 C)
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)
10
Q
savanna climate and physiognomy
A
diverse climate= diverse physiognomy
- high rainfall = more tree cover
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
12
Q
savanna parkland
A
tall mesophytic grassland (grasses 40-80 cm high) with scattered deciduous trees (<8 m high)
13
Q
savanna grassland
A
tall tropical grasslands without trees or shrubs
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)
15
Q
thicket and shrub savanna
A
communities of trees and shrubs with out stratification
16
Q
origins of savannas - climate ?
A
climate alone cannot explain as closed canopies and open savanna occur under the same climatic conditions
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
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
19
Q
characteristic life forms
A
(1) trees; phanerophytes
(2) grasses; hemicryptophytes
(3) woody succulents/ caudiciforms; chamaephytes, cryptophytes
(4) succulents
(5) forms/annuals ; therophytes
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
21
Q
adaptation of grasses in savannas
A
(1) rhizomatous
(2) adventitious roots
(3) scleromorphic leaves
(4) many C4 species
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
23
Q
C4 mechanism in grasses
A
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)
25
why do savanna trees have flat tops?
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
26
savanna phenology
- 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
27
Succession- savanna fires areas of occurrence
Grassland savannas
-continuous grass cover
- fuel load of > 1 t h -1
28
Succession- savanna fires area where fires do not occur
- semi-deserts
- thorn savannas (bushveld)
- seasons of above average rainfall
29
savanna fires - causes
(1) lighting
(2) humans; to maintain and improve pastures, clear land and increase fertility, keep wild animals away, eradicate vermin (snakes)
30
savanna fires - characteristics
-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
31
Vegetation type and fire characteristics; Grasslands
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
32
Vegetation type and fire characteristics; African savannas
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
33
savanna fuel characteristics and types of fires
- 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
34
savanna fires; consequences --reduction of above group phytomass
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
35
savanna fires; consequences --effects on soil
(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
36
savanna fires; consequences --trees, effects and responses
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)
37
savanna fires; consequences -- grasses, effects and responses
- 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
38
Grass/Tree interactions: the "Gulliver Effect"
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
39
Factors promoting Gulliver suppression --> Grasslands
- frequent fires
- browsing animals (elephants, porcupines, etc)
40
Factors promoting Gulliver release --> Woodlands
- fire suppression
- reduction in fuel load --> grazing, drought (increase in fire intervals)
41
savanna fires; consequences -- community structure
fire produces a large scale patchwork/mosaic of areas at different stages of succession --> fire climax formation
42
Savanna productivity
intermediate between tropical forests and deserts. variable, affected by rainfall (amount, season) and burning
43
savanna nutrient cycling
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
dung beetle
important in rapid decomposition of dead organic materials. dung beetles research on if they use the stars as a gps
45
termites
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
Plant herbivore interactions; adaptations which reduce herbivory STRUCTURAL DEFENSE
grasses - location of meristem , silica cells , and hairs
trees - thorns, affects bite size `
47
Plant herbivore interactions; adaptations which reduce herbivory CHEMICAL DEFENSE
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
Plant herbivore interactions; adaptations which reduce herbivory RESOURCE PARTITIONING
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
Plant herbivore interactions; adaptations which reduce herbivory SEASONAL MIGRATIONS
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
threats to savannas
(1) global climate change
(2) bush encroachment
(3) desertification
51
global climate change
"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
bush encroachment
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
desertification
- 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
causes of desertification-- irrigated croplands
- 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
causes of desertification-- rain fed croplands
- 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
causes of desertification-- grazing lands
-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
causes of desertification--overconsumption of fuelwood
-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
causes of desertification-- increased sedentary population
-increased population and livestock pressure on marginal lands
59
causes of desertification--climate change
- more rapid with desertification
- more variation in climate increases desertification potential
- hotter and drier conditions make desertification more likely
60
solutions to desertification
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
arid
excessively dry; insufficient rainfall
62
tropical forests productivity
productivity: rate of accumulation of energy or biomass
high for tropical rainforests because of: light, water, mesic temperatures, low seasonality
63
nutrient cycling
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
tropical forests nutrient cycling
(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
tropical forests; replenishment of soil nutrients from...
(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
mechanisms that enhance nutrient uptake
(1) mycorrhizae
(2) surface roots
(3) sclerophylly
67
tropical rain forests show fragility to ...
(1) clearing
(2) slash and burn
(3) logging
68
deserts- geographic distribution
20% of acid areas are covered by sand
- 2% in North America
- 45% in Central Asia
- 28% in Saharan
69
defining a desert
(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
types of desert
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
desert precipitation
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
desert temperature
-reflects geographic position 4 - 40 C
- at extremes, temperature can control plant growth
73
desert soils -- salinity
- ascending water: high calcium carbonate and higher pH to alkaline (basic or greater than 7)
- evaporation concentrates salts
74
desert soils -- desert pavement
-surface of angular, interlocking fragments of pebbles, gravel, or boulders in arid areas.
75
desert soils -- water
- 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
climate variability v heterogeneity
climate variability emphasizes temporal variability of water input
heterogeneity emphasizes spatial variability of water availability
77
species diversity
decreases with increasing environmental stress
tropical forest > savanna > desert
78
desert growth form diversity
-high
- reflects spatial and temporal (relating to time) heterogeneity (diversity) of the water supply
- reduces competition for a limiting resource
79
desert -- adaptations of plants to arid environments
- adaptations reflect the impact of water stress on carbon economy
- different strategies have different survival values versus growth potential
80
survival strategies -- drought escaping
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
survival strategies -- drought avoiding
(1) water spenders
- high water uptake
- high growth rates
(2) water savers
- reduced water loss
- high survival
82
survival strategies -- drought tolerating
(1) dehydration avoiding
(2) dehydration tolerating
loose water during drought
partial -----> total
protoplasmic dehydration
survival under extreme drought
83
drought escape : therophytes
- annuals complete their lifecycle in < 8 weeks
- rainfall triggers germination
- germination is rapid , 1 h
- life cycle is rapid
84
drought escape : therophytes -- show phenological/ phenotype plasticity
- 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
drought escape : therophytes -- seed banks
- soil
- surface
- variable densities
- lowest in washes
- distribution altered by foraging ants
- foraging decreases densities BUT provides germination sites (ants) and seeding competition
86
drought escape : therophytes -- safety mechanisms
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
amphicarpy
- 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
Mycorrhizae
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
Surface roots
Roots grow towards the surface to access sufficient oxygen and nutrients that may be lacking in the soil.
90
Sclerophyll
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
Slash and burn
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
Give the reasons crop yields decline rapidly when crops such as corn are planted in areas cleared of tropical forests.
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
Even if farmers in the tropics have enough free capital to purchase fertilizer, this is probably not a good solution. Why?
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
Ideas for good solutions? (Nutrient cycling Q)
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
Deciduous
Shedding its leaves annually
96
Phanerophytes
Buds on exposed branch tips:trees
97
Chamaephytes
Buds close to the ground, protected by snow
98
Hemicryptophytes
Buds at soil level, protected by dieback
99
Cryptophytes
Bulbs, rhizomes, corms, etc., protected by soil
100
Therophytes
Seeds
101
Rhizomatous (grass adaptation)
Horizontal form of plant stem that grows underground which can form roots and shoots that grow into a new plant
102
Adventitious roots
Plant roots that form from any non root tissue in response to stress conditions such as flooding, nutrient deprivation and wounding
103
Scleromorphic leaves
Firm and stiff leaves with thickened epidermis and cuticula but with mechanisms to promote water transport under beneficial conditions
104
productivity of savanna
mean 900. less than tropical rain forests but more than woodlands and grasslands.
