Transcript An attempt to differentiate climatic and human induced

An attempt to differentiate
climatic and human induced
changes on vegetation in
Botswana
A.C. Chipanshi [[email protected]]
S. Ringrose
W. Matheson
R. Chanda
Background/Introduction
• Impacts of humans/animals on veg is low
at low population densities
• Impacts of climate  climax veg
(confounded by episodic events)
• Natural and human forces are not mutually
exclusive
Objectives…
• Develop an up-to date map of veg cover
since first one was made in 1971
• Suggest possible changes to vegetation
using climate change scenarios
• Indicate adaptive and policy options to
resources managers
Study area details
• Botswana sits astride the Tropic of Capricorn and
hence it has an arid-like climate
• Low human population (~1.3 million) but has high
growth rate (3.5%); area of 582K km2
• Settlement is skewed in favour of the SE
• Domesticated animals are estimated at 3 times the
human pop (cattle & goats ~ 4.8 million)
Location map of the study area
Moisture Fields
Vegetation types, 30 years ago
• Early mapping based on photos and field
surveys (Weare and Yalala)
• Noticeable trend with moisture gradient
• No one species dominates the landscape
Map of vegetation types in the 1960s
Implications from the early
mapping
• Degradation due to human activities low
• Species diversity quite widespread
• Fires and droughts were the main agents
controlling vegetation dynamics
Current Mapping (1995)
• Thematic Mapper: bands 3,4,5 were used
• Mapping supplemented by field work for species
type and density assessment
• Current mapping reveals changes in species type
and density
Vegetation map in 1995
Summary of the satellite mapping
1995)
• Arid shrub savanna coincides with 1971 map
• Kalahari bush savanna degraded most on eastern
side but less so on west
• North of Kalahari, dense tree and bush savanna is
followed by sparse savanna (reverses 1971)
• Floodplain area is now a mixture of shrubs but this
was grassland in 1971
• Bushy species are more common in east than
elsewhere (Terminalia sericea)
Lessons from the map intercomparison
• In the less settled west, climate appears to
be the dorminant factor on vegetation
• In the east and northern fringes, there
appears to be an accelerated rate of
vegetation density and species change
(humans and climate)
Projections into the future
• Climate change experiments suggest
warming in Botswana (1 to 2o C above
present climatology) in next 50yrs
• Rainfall shows a decrease by 5 to 20% by
most models and composites
• What vegetation biomes can we expect?
Biome model outputs from GCMs
for the 2050s (After Hulme)
Biome class
'dry'
'wet'
'core’
Rain forest
-20
+15
-30
Seasonal forest
+10
+10
+5
Dry forest
0
+15
+10
Tree and shrub savanna
0
-15
-10
Thorn shrub savanna
+30
-40
+30
Grassland
-50
-30
-55
Desert
-5
-15
+10
Summary of changes likely to
impact vegetation
• In all scenarios, grassland degrades into dry
forest or tree and shrub savanna
• In dry and ‘core’ scenarios, forests decline
and thorn and shrub savanna expands
• Over all degradation of present biomes
What adaptive options do we
take under these conditions?
• Informed tree planting programmes
(ATHTP vs. ATPP)
• Community Based Natural Resources
Management strategies (e.g. communal
rangelands) are a good adaptive strategy
• Include indigenous knowledge
• Diversify rural economy
Policy Options
• Carry out inventories at regular intervals
• Reform land tenure to allow open access to
forestry resources in less degraded areas
(state land and commercial properties)
• Involve communities in managing forestry
resources
CONCLUSIONS
• Changes that have taken place in vegetation cover
in the past 30 yrs (trees to shrubs) are expected to
continue in the near future
• Both human and natural forces are contributing to
forestry degradation (difficult to separate)
• Current adaptive and policy arrangements are not
sufficient; community based approaches are the
options