Transcript Document

Rangelands in the New Millenium:
geographical reflections on the VIIth
International Rangeland Conference,
Durban, 26 July – 1 August 2003.
Kate Rowntree
Catchment Research Group
Department of Geography
Rhodes University
Rangelands are those natural
and semi-natural ecosystems
in which husbandry of large
herbivores is the principle
economic activity
Geographic importance of
rangelands in Africa
• 70 % of the land area is occupied by
rangelands
• Importance of livestock to livelihoods
• Includes conservation areas
• Concerns for land degradation
Rangelands in Africa
Fire and grasslands
Cattle densities
Key characteristics
• Located in drier parts of the continent
• Productivity closely linked to spatial and
temporal variability of moisture
availability
• Unpredictable systems
• Drinking water as a limiting factor –
significance of watering points
Models of rangeland
management
Sue Vetter & others
• Equilibrium model
• Non-equilibrium model
EQUILIBRIUM CARRYING CAPACITY MODEL
Long term
rainfall
Climax
vegetation
Sub-climax
vegetation
Degradation
Livestock
numbers at
carrying capacity
Livestock
numbers above
carrying capacity
700
Annual Rainfall at Aberdeen
Annual rainfall (m m )
600
500
400
300
mean
200
20% percentile
100
0
1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980
Equilibrium model:
conventional paradigm
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•
•
•
Based on a fixed carrying capacity
Rotational grazing
Supplementary feeding during droughts
Purchase of cattle to make good stock losses
during a drought
EQUILIBRIUM CARRYING CAPACITY MODEL
Communal rangeland
Long term
rainfall
Sub-climax
vegetation
Degradation
Livestock
numbers above
carrying capacity
NON-EQUILIBRIUM MODEL (Ellis and Swift 1988;
Behkne & Scoones 1993)
Variable
rainfall
Variable
vegetation
biomass
Variability in time and space
wet spells
drought
Stock numbers increase
Mortality reduces numbers
Fluctuating
livestock
numbers
700
Annual Rainfall at Aberdeen
Annual rainfall (m m )
600
500
400
300
200
mean
median
20% percentile
100
0
1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980
Non-equilibrium model
• Vegetation condition related to rainfall
rather than grazing pressure
• Stocking rates variable: coupled to
vegetation & therefore to rainfall
• High mortality during droughts
• Importance of recovery period after drought
• Mobility exploits local spatial variability in
rainfall
Response to drought
• Equilibrium model:
– supplementary feed and restocking
– no lag in recovery of stock numbers after
drought
• Non-equilibrium model
– high stock mortality
– recovery of stock numbers tracks recovery of
vegetation
Key Resources
Andrew Illius & Tim O’Connor
• Those resources that support livestock
during the dry season
• Livestock numbers coupled to key resources
• Wet season grazing pressure dependent on
dry season key resources
• Supplementary feed increases pressures on
non-key resources
Pattern & scale in landscape
heterogeneity
Dryseason
grazing
3
e.g upland
zone; flood
plain
2
1
Mobility and drought
• Seasonal drought: Movement between
landscape units to utilise key resources
• Local drought: spatial variability of
rainfall, movement within available
territory, stock numbers maintained.
• Regional drought: too widespread to be
mitigated by movement, mortality of stock.
• Ability to cope with drought depends on
available territory.
Fragmentation
Tom Hobbs
Causes: fences
Changes to ownership
Land use change (to cultivation)
Dryseason
grazing
3
e.g upland
zone; flood
plain
2
1
Complexity in rangeland
ecosystems
• Cascade effects in the landscape (Tim Hoffman)
– Removal of woody skeletons
• Loss of protection for seedlings
• Loss of insect nesting sights
– Loss of pollinators
• Importance of life cycles (Peter Carrick)
– Browsing flowers reduces regenerative capacity
– Unpalatable species may have palatable flowers
– Livestock can spread seeds
• Ability of a plant community to regenerate is a
key consideration
Who are the grazers?
Mark Dangerfield
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•
•
•
termite biomass - 70-110 kh/ha
ungulate biomass 10- 80 kg/ha
turnover by termites120 kg/ha
nests become foci of nutrients. In Okavango
can eventually form islands due to
vegetation growth on nutrient rich soils.
• importance of concentrating resources in
small areas - landscape heterogeneity.
Range management in dynamic
systems
• Many development strategies have been based on
the equilibrium model
• The non-equilibrium model may be a better basis
for rangeland management in drier areas
• Key components of a N-E development strategy:
– Mobility (reduce fragmentation)
– Slow recovery of stock numbers after drought
– Strategy to maintain livelihoods following stock
mortality
– How do you maintain a stable livelihood in a dynamic
system?
• Who uses rangelands and for what?
– Ranchers, conservation areas, water catchments
• What is the contribution of rangelands to
livelihoods?
• What are the impact of global changes on
rangelands?
• Lack of understanding of the temporalspatial variability in these complex,
dynamic systems.
• Lack of concensus as to best way to manage
these systems.
Rangeland management – emerging themes
Topographic gradients
Landscape
ecology
livestock
Rainfall variability
Economics &
livelihoods
Human
adaptation
Culture
Governance