An attempt to differentiate An attempt to differentiate climatic and human induced climatic and human induced changes on vegetation in changes on vegetation in BotswanaBotswana

A.C. Chipanshi [Chipanshia@em.agr.ca]

S. Ringrose

W. Matheson

R. Chanda

Background/IntroductionBackground/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…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 detailsStudy 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 areaLocation map of the study area

Moisture FieldsMoisture Fields

Vegetation types, 30 years agoVegetation 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 Implications from the early mappingmapping• Degradation due to human activities low

• Species diversity quite widespread

• Fires and droughts were the main agents controlling vegetation dynamics

Current Mapping (1995)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 Summary of the satellite mapping 1995)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 inter-Lessons from the map inter-comparisoncomparison• 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 futureProjections 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 Summary of changes likely to impact vegetationimpact 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 What adaptive options do we take under these conditions?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 OptionsPolicy 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

CONCLUSIONSCONCLUSIONS• 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