Modelling the impact of water management scenarios · PDF fileModelling the impact of water...

Modelling the impact of

water management scenarios

Jelle Hilbers, Frank van Langevelde, Herbert Prins, Rina Grant, Mike Peel, Michael Coughenour, Henjo de Knegt, Rob Slotow, Izak Smit, Greg Kiker,

Fred de Boer

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• Elephants are considered to be “ecosystem engineers”

• They influence vegetation structure and composition

• Cascading effects have been reported:

• Fritz et al. (2002): mesobrowsers are negatively affected

• Kohi et al. (2011): mesobrowsers are positively affected

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• High densities of elephant in KNP do concern park management

• Changing surface water provisioning is a suitable strategy

• Construction of water points (WPs) extensively studied

• Changes in spatial distribution and densities of elephants-> cascading effects on vegetation and other herbivore species

• In KNP almost half of the remaining functional WPs are under consideration to be closed

• But: still unclear what the effects of WP closure are

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We examined long-term effects of different scenarios of WP closure in KNP on the spatial distribution of elephants

calculated the cascading effects on the vegetation and other

browser and grazer species

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• Study area:

Kruger National Park

– 20,000 km2

– 6 perennial rivers

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• Scenario 1

All WPs re-open

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• Scenario 2:

“Current situation”

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• Scenario 3:

Future situation:

reduced number

of WP

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• Scenario 4:

All artificial

WP closed

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• We used the SAVANNA model (Mike Coughenour) – Spatially explicit, process-oriented

– Landscape-scale

– Grid-cell (25 km2) based

– Monthly time-steps

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Parameterisation: – 11 herbivore species

• Mesograzers: buffalo, roan, wildebeest, zebra

• Mixed feeders: elephant bulls, elephant herds, impala

• Mesobrowsers, browsing heights: four classes (0-100 cm, 101-200 cm, 201-300 cm and >300 cm) for: steenbok, bushbuck, kudu , giraffe

– Distribution based on:

Forage biomass, Distance-to-water, Shade, Accessibility, Slope

• Animal populations kept constant at 2010 estimates

• Parameter values: scientific literature, expert knowledge, GPS data of collared elephants

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• Water point management 1 (Re)Opening all WPs

3 Future situation=reduced

• Natural water availability (rainfall) – Very wet

– Intermediately dry

Scenarios

2 Current situation=intermediate

4 Closing all artificial WPs

– Intermediately wet

– Very dry

Rainfall scenarios

very wet

intermediately wet

intermediately dry

very dry.

WP scenarios:

1 opening all

2 intermediate=current

3 reduced =future

4 closing all

1 2 3 4

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• Elephant density – Present (2010) elephant numbers

– Present (2010) elephant numbers -50%

– Present (2010) elephant numbers +50%

Scenarios (further):

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• 80 consecutieve years: we used last 20 (60-80) years only

• 48 scenarios

• 5760 maps per animal species or plant group

• Average animal densities (#/grid cell) and plant biomass (g/m2) in buffers along the rivers: 0-5 km, 5-10 km, 10-20 km, 20-40 km, 40-60 km

Simulations

What did we find ?

• Under very wet and intermediately wet conditions

-> hardly any effects of WP closure

If you remember this, we are already happy

How to read output

Buffer zones strips

Current numbers

Scenarios

Species

<-Very wet

Intermediately wet ->

<- Intermediately dry

Very dry ->

Strong reaction of small

trees

closed

Grass & Tree effects

WP closure : predicted effects

– Woody biomass: most biomass found within 40 km of rivers; mostly at small distances (0-5 km) 0-1 m class reacts strongly to closure (> 10km)

– Grass biomass: generally unaffected

<-Very wet

Intermediately wet ->

Redistribution of game does not take place when it is very wet or slightly wet

<-Very wet

Intermediately wet ->

<- Intermediately dry

Very dry ->

Redistribution takes place

when it is very dry and when WPs are closed

Very dry:

Current numbers

Scenarios

Impala , roan, buffalo

Influence of elephant density

• Hardly any changes in spatial distributions and total grass and woody biomass as result of changes in elephant density

(+ 50% or – 50%)

• Even no effects during very dry conditions

<-Very wet

Intermediately wet ->

<- Intermediately dry

Very dry ->

Influence of elephant density:

• Hardly any changes in spatial distributions and total grass and woody biomass due to a change in elephant density

• Therefore also hardly any changes in distributions of other animals: cascading effects are basically absent

<-Very wet

Intermediately wet ->

<- Intermediately dry

Very dry ->

Influence of elephant density:

• Hardly any changes in spatial distributions and total grass and woody biomass due to a change in elephant density

• Therefore also hardly any changes in distributions of other animals: cascading effects are basically absent

• The reason is that total biomass consumption of “all these elephant” is actually very low !

So what are the effects of WP closure ?

• Only during drought episodes effects were found – Comparable to statements of Smit and Grant (2009) and Mwakiwa et al.

(2012)

– Under very wet and intermediately wet conditions , animals not water –limited -> effects of WP closure unimportant

• Plans of KNP management to permanently or temporarily close almost half of the functional WPs will hardly have any effects; only under very dry conditions an effect is predicted.

• Perhaps keep a water infrastructure in place to be “turned on” during a drought.

Species effects of WP closure

• “Other herbivore species” far more affected than elephant, but steenbok and giraffe (which are not affected)

• Studies on WP construction and closure however often focused on elephants (Owen-Smith et al. (2006), Chamaillé-Jammes et al.

(2007), Smit et al. (2007), Van Aarde et al. (2008), Loarie et al. (2009), Smit and Grant (2009))

• More research needed on the “non-elephant”

Thank you for your attention!