Download The development of vegetation

The development of
vegetation
F.6 Geography
The classification of plants
1. Life form of plants
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Trees (perennial 常年)
Shurbs
Lianas (藤本)
Herbs (草本)
Vegetation structure
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Forest
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Woodland
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Lichens
Factors influencing Development
1. Plant habitats (生存環境)
It is affected by landforms and soil
2. Soil Water availability
Xerophytes ( 旱生植物)
 Hygrophytes (濕生植物)
 Mesophytes (中生植物)
Minor classification
 Tropophytes ( 旱濕並生植物)
 Deciduous plants (落葉植物)
 Evergreen plants (常綠植物)
 Sclerophyllous plants (硬葉植物)
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3. Temperature
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Affect rate of photosynthesis, flowering,
fruiting ,seed germination
Too hot will increase evaporation of plants
Too cold will damage cell tissue
Frontier : it means the plants can live within
this boundary
Imply : Every plants have their limit of
distribution
4. Time
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Ecological succession (生態演替)
Plant and animal will succeed one another
until the environment is stable for growth
Climax vegetation (頂極植物)
- It means the plants reached the stable
community
Sublimax plants (次頂極植物)
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It mean a stable situation by non-climatic
controls
Reasons for succession
~ Plants compete for suitable environment to
survive
~ As environment always change , it favours
different plants at different time
Process of succession
1. Pioneers ( 先鋒植物) first
~ usually annual herbs and weeds
2. Grass and shurbs move in (10 – 20 yrs)
3. Pine seedlings (幼苗), form a shaded cover, changing
climate
4. Pine forest mature (50yrs) ,board leave deciduous
tree come (oak and hickory forest)
5. It form a mature forest finally , the climax forest is
formed. (become stable and unchanging )
Common features found in climax stage
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Mature soil
Height of plants increase and strata form
Biomass and productivity increase
Number of species increase
New microclimate form within forest
Different species replace other until a climax stage
form
Final community is stable than the first one
In TRF, plant succession occur rapidly (50yrs)
In tundra ,slow
Other influence on succession
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Forest fires
Severe storms
Insects
Disease
Human activities
If a forest is disturb by these factors , a
subclimax vegetation is formed
Human impacts on vegetation
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Clearing forest disturb climax vegetation
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The invasion of a plant disease by other
countries cause extinction of particular plants
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Farming, mining, addition of fertilizer may
change soil structure or affect plants growth
Case study (China)
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Increasing population ,greater demand for
cultivated land all increase pressure of cutting
forest
This happened seriously in North China Plain
Also, during war time , many people migrate
to South China ,therefore, increase pressure for
farmland there
Today, only 12% remained as forest in China
Global and local plant environment
relationship
TRF
~ Amazon Basin in South America
~ Congo Basin in Africa
~ The Malay Archipelago in South East Asia
~ Central America , west coast of Africa, India,
Sri Lanka, Australia
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Characteristics of vegetation
Lack of seasonal variation ,plants lost leave in
different times
 Vegetation layer
~ usually have five layer
Leaves
~ uniform , dark green, glossy (光滑), leathery,
oval and broad-leave
~ leathery due to thick cuticle (reduce
transpiration)
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Drip-tips (滴水葉尖)
~ Allow plants to shed excess water
Butress root (板根)
~ support the great weight
Cauliflory (莖花)
~ the trunks or smaller trees bear flowers and
fruit directly (example : cacao tree)
Types of vegetation
Tree species
 About 6000 species in Congo
 Mainly hardwoods, mahogany(紅木),
ebony(烏木), wild rubber tree
Climbing plants
Plants have twining habit
Example: lianas
Epiphytes (附生植物)
~ ferns ,orchids, mosses and lichens
~ mainly live underground ,so called
undergrowth
~ cause no harm to host
Parasites (寄生植物)
~ extract water and nutrients from host
Stranglers
~ originally growth like epiphytes , then put out
long pendant roots to get nutrients from soil
~ when they growth up ,their root thicken and
increase in number , kill the host finally
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Tree ferns
~ a kind of herb, growth mainly on shaded sites
and often six metres high
Undergrowth
~ can live in lower light environment
Saprophytes (腐生植物)
~ no chlorophyll (葉綠素)
~ using symbiotic (共生根) fungi in roots
~ can live on dead organic matter
Vegetation of tropical shores
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Mainly mangroves near tropical shores
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Have prop-roots(支柱根), sharply arched or
growing straight up from the mud
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The radicle (胚根) stuck in the mud to form a
firm root
Plant succession and human impacts
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High nutrients stored in plants , but little in soil
and litter
Shifting cultivation increase pressure to clear
land for planting
Secondary forest may appear ,xerophytic plants
may appear , lower dominant trees, more
undergrowth and less clear strata than the
primary type
Need long time to restore (250 yrs)
Tropical Desert vegetation
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Sahara Desert
Arabian Desert
Atacama Desert
Namib Desert
Kalahari Desert
West-Central Australian Desert
Characteristics of the vegetation
Morphological characteristics
~ development of extensive root system which
may be vertical or horizontal
~ deeply penetrating roots (e.g acacias, mesquite)
~ horizontal root are common in sandy or
shallow soil overlying harder substrates, it may
extend for 5-20 metres,just below surface
~ low shoot to root ratio 莖根比例( 1:3.5 to 1:6)
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Reduce the transpiration surface, plants have
small leaves or even no leaves, shed foliage,
roll leaves,etc.
Some leaves reduced to spines
Anatomical 組織characteristics
~ heavy cuticularisation (角質化過程) and
cutinisation (角質化) produces a watertight,
varnish-like covering to reduce water loss
~ lignification (木質化)
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Low, round shapes , like those of cushion
plants and small cacti, can reduce structural
damage from even strong wind
Many hairs
Stomata are arranged in recesses(凹處) or
grooves (細槽) to help in retaining water
Few organic matter as will eaten by termites or
blown by wind
Low biomass , so lack of competition
Each stand is very far away
Types of vegetation
~ Ephemeral annuals (短生植物)
~ 50-60% of desert plants
~ 6 – 8 weeks
~ remain as seed in the dry seasons
~ desert plantains and desert fescue
~ small size and shallow roots
~ winter annuals appear in temp 15-18C
~ summer annuals appear after the first heavy
rain of summer at 26 – 33C
Succulent perennials (多年生植物)
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Enlarge parenchyma (薄壁組織)
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Their stems or leaves allow the accumulation
and storage of water during rainy seasons ,e.g
saguaro cacti
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The stomata are closed at day and open at
night
Non-succulent perennials
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Plants that are adapted to arid climate
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Herbs, grasses, shurbs, trees
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The seeding produces the first leaves ,then above-ground
growth stops for several months while the root system
penetrates deep into the ground
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Can found in wadis, oases or near perennial river
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Examples include tamarisks, acacias grasses and palms
Plants succession
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Cultivation cause soil erosion in desert
Cutting and grazing cause dominance of plants
The selection of some species for medical
purposes cause extinction of certain plants
The expansion of a desert that a desert
ecosystem over regions that are not naturally
deserts
Climax vegetation in desert only happen for a
short time because the soil are too mobile
Tundra Vegetation
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Characteristics of the vegetation
Adaptation to the low temperature
Adaptation to the short growing seasons
Adaptation to strong wind
Adaptations to permafrost
Adaptation to physiological drought
Decay slowly in tundra
Food Storage
Types of vegetation
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Few hundred found
Small, stunted, xerophytic characteristic
Trees- spruce, larch, pine
Mosses and lichens
Grass and sedges (most common )
- Heathers, reindeer moss, cotton grass
Flowering plants – poppies
Local plant-environment
relationships
Altitude zone vegetation characteristics
~ temperature drops
~ precipitation usually increase
~ relative humidity increase due to the cooling of
air
~ light intensity and day time warming increase
~ outgoing radiation also increase , greater
diurnal range in temperature
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Clouds form at great height because dew point is
easily reached
Orographic effect cause different rainfall on different
sides
Permanents snowcaps may exist on high mountains
Winds also increase ,leading to windy exposed upper
slopes
South facing slopes , drier. North-facing slopes, under
the shape for a long time
Great changes in the environment over short distances
(steep environmental gradient )
The relationship of biomes to
Ecoclines
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Environment gradient (環境梯度)or ecocline
(生態變異)is a gradient along which the
communities and environment change
Gradients analysis (梯度分析)looks at the
changing condition across an ecosystem
boundary
An ecotone (群落過度帶)is a transition zone
or overlap between two ecosystems
The main biomes
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Tropical rain forest
Savanna or tropical grassland
Desert
Temperate forest
Coniferous forest
Tundra