Man environment
relationships in TRF
F.6 geography
The impact of the
environment on man
The Amazon Basin
Slash and burn or shifting cultivation is
most common
The soil will rapidly depleted after one to
two crops, the cultivators are forced to
leave the clearing site and move to a
new one
The process
Selecting the site
Clearing the forest
Burning off the dead vegetation
Planting crops
Weeding and harvesting the crop
migration
Selecting the site
Clearing is easy in primary forest cause
little undergrowth
The secondary forest also dries out
more easily
A steep hillside is usually choose
because there is updraught to spread
the fire
Clearing the forest
Take place at dry seasons
It is done by simple hand tools
Such method may protect the virgin
forest
The tallest trees cut down first , it will
drag down shorter tree on the path
Burning off the dead
vegetation
The ashes will enrich the soil
Heavy clay soil dried out ,developing
large cracks in which ash accumulates
People use only small digging sticks
and hands hoe (鋤頭）for ploughing
The debris after burning off helps to
reduce runoff and reduce erosion
Planting crops
Multi-storey agriculture are easily found
Yams are the ground crops
Millet are lower storey
Manioc beans or maize the third storey
Bananas, breadfruit ,other tree
crops ,the upper storey
Advantages of mixed
cropping
Reduce the amount of space to cleared
Lengthen the seasons of growth
Enables maximum return for the
minimum effort
Provides more complete cover,shading
the ground and prevent the growth of
weeds
Different crops allow the best use to be
made of soil, sunshine and rainfall
Provides insurance against the failure of
any one type of crops
Ensure a more constant supply
Seeds are sown by mouth (spitting) or
by using a primitive seed drill ( 種子鑽
子) (a hollow stick which enables seed
to be dropped into the holes without
having bend over )
The main crops are maize, pulses,
green vegetables, yams and manioc
(cassava)
Crop rotation helps to prevent soil
exhaustion and erosion
Weeding and harvesting
The swidden receives little attention
during the growing period
Root crops can be left in the ground and
dug up as required – one root crop
providing enough food for a family for
several days
Vegetables are hand-picked. When
ready, cereals are dried, threshed (打穀）
and husked （去穀類外皮 )
Migration
Tropical soil depleted easily (1 to 3 yrs)
Weed and undergrowth will invade
easily at that time when the nutrient loss
Farming will leave the clearing and look
for a fresh site
This allows the forest to reclaim the
clearing and rebuild soil fertility. This is
called bush fallowing
Natural hazard also cause migration :
disease like malaria and sleeping
sickness, disasters such as insect
plagues and droughts and animal
invasion
The land can be reused after a 8-20
year of bush fallowing when soil fertility
has been restored
The village and way of life
Location : usually near the stream ,for
food, transport, domestic use
Plan : 20 to 300 people ,in a single
street or circular group
Typically village house : village house
(long house)are elevated because avoid
wet climate, termites, tigers and
panthers (黑豹）cannot invade the
house
Way of life
Use primitive tools
Fishing , hunting ,farming , weeding ,
harvesting, gathering
Plantation : cacao, cotton and rubber
Difficulties in timber production
The wet and hot climate prevent people
development of the TRF
Species are mixed, no pure stand ,making
cutting difficult
Hardwoods have thick trunks and buttress
root and are difficult to fell
Transport difficult
Swampy ground
Insects ,disease
Lianas ,climbers make movement in forest
diffcult
The impact of man on environment
The ecological impact of shifting
cultivation :
- the direct burning of the organic matter
can speed up the oxidation of the
organic matter and humus in the top soil
- the primitive method can reduce
structural damage to the soil. No
chemical are used and thus no
environmental hazards result
In some area, weeding is done
manually and selectively to preserve
trees seeding and spalings , adding
forest regeneration
No draught animals are used ,so the
return in relation to input is very efficient
Shifting Cultivation add variety to their
food by hunting, fishing,gathering
The full vegetative cover can reduced
erosion ,while multiple cropping reduce
pest and disease hazard
Abandoning the clearings
Abandoning can cause soil erosion ,
structural damage and fertility decline
together with weed invasion and disease
Long fallow period is need if want to resume
fertility
Managed rotation of fields is better using the
corridor system (走廊式輪植法)
If shifting cultivation is subsistence purpose ,it
pose lesser harm to the environment
Deforestation
It generate many problems :
Displacement of the rainforest
Changes in the hydrology of the
Amazon Basin accelerate surface
runoff ,reducing infiltration , modify the
fluvial regime
Variation in run-off ,sediment load .
Sedimentation are prevailed
It will affect aquatic plans and animal
Deforestation may produce climate
changes such as change in soil
temperature, humidity, wind speed and
insolation
Biomass reduction – it leads to soil
erosion ,nutrient loss
Cattle ranching
The removal of TRF for cattle ranching
free nutrients from the biomass
producing a reduction in nutrients
The pasture deterioration can lower the
carrying capacity of land from 200 cattle
/km² to 50-80 cattle /km²
Overgrazing, trampling and soil
compaction also lead to accelerated
erosion or poor drainage
Effects on aquatic
resources
Reduce the supply of organic debris
which is an important food supply for
fish
It can alter run-off and erosion ,affecting
the productivity of the streams by
altering the water quality
Increasing population
Increase pressure upon food producing
land and reduce the period of essential
bush fallow
Old clearing are reused sometimes,
forest replaced by woodland or open
grassland
Introduction of European agricultural
technique
Geometrically arranged fields have
reduced the protective ground cover,
accelerating soil depletion through
leaching
The introduction of deep ploughing and
steel ploughs also increased erosion
because they allow plots to be
completely cleared ,exposing soil for
erosion
Cash cropping brought changes in the
life of the tribes (it brings personal gain
and the possession of the land )
Other effect :
- Mining leaves behind mining pits full of
water , it favour the development of
malaria
Land development solution
An economically productive and
ecologically stable system is need
One of the method is
compartmentalizing (分隔) the
landscape ,then apply separate
management strategies to each unit
Use of the varzea
Varzea is a place which have higher
potential land
Intensive agricultural and use of
aquatic resources can be practised here
But it should be controlled with a fixed
fishing season and limited on the fish
caught
The terra firma
To protect the terra firma(upland
savanna and forest ), there would be
low intensity,shifting cultivation and
plantations of selected tree and shrub
crops
Large scale forest clearance for farming
and ranching in these area would be
stopped
Agricultural alternatives
Agricultural/ silviculture ( 農耕做林學）
is a possible alternative
The inter-planting of annual food crop,
perennial food crops and slow-growing
timber species
This system is a compromise between
crop production and land protection
Population control
This can be used to prevent too much
pressure on the land
Educational programmes to encourage
some form of family planning are
necessary
Native participation
Cash cropping can allow specialization
and capital formation in these
underdeveloped areas
The tribes can use these profit to buy
fertilizers ,tools and transport. Thus,
improving the living standard