Droughts Decouple African Savanna Grazers from Their Preferred Forage with Consequences for Grassland Productivity

Droughts decouple African savanna grazers from their preferred forage with consequences for grassland productivity

Donaldson J; Archibald S; Parr C; Mangena H; Mkhonto K Grazer – grazing lawn feedbacks

Sally Archibald

Mc Naughton 1979,1984,1985; Augustine et al. 2003; Archibald 2008; Waldram et al. 2008; Anderson et al. 2010; Cromsigt & Te Beest 2014 Tussock grass communities What happens in a drought? • Drought and grazing intensity interact to affect grass community structure in savanna rangeland systems (O’Connor 1995)

• Simulated grazing under drought conditions decreased productivity in tussock grasslands (Koerner & Collins 2014)

• Grazer use of local grass communities change (reserve forage; Macandza et al. 2004)

• Regional migratory responses occur, but vary between ungulate species (Augustine 2010) 1. How does herbivore use of different grass types change during and after a drought?

2. How do these changes affect grass productivity post-drought? Satara study system

Sally Archibald The drought years…

1200

1000

800

600 Rainfall (mm) 400

200

120 Rainfall season

100

40 Rainfall (mm)

0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 2015 2016 Measuring ANPP Dung transects Permanent exclosures Five grazing Mobile lawns exclosures

Five tussock

grass 50m

Five Burned- tussock grass 4m The drought years… Lawn grass Tussock grass Burned - tussock grass The drought years… Lawn grass Tussock grass 1 Burned - tussock grass 0.8

0.6

of grass bitten of grass 0.4

0.2

0 Proportion Dormant Growing Dormant Growing season season season season 2015 2016 2017 End 70 60 50 40 30 20 10

Dung counts per per month Dungcounts 0 Dormant Growing Dormant Growing season season season season 2015 2016 2017 End The drought years… Lawn grass Tussock grass 1 Burned - tussock grass 0.8

0.6

of grass bitten of grass 0.4

0.2

0 Proportion Dormant Growing Dormant Growing season season season season 2015 2016 2017 End 70 60 50 40 30 20 10

Dung counts per per month Dungcounts 0 Dormant Growing Dormant Growing season season season season 2015 2016 2017 End

Owen-Smith & Traill 2017 The drought years… Lawn grass Tussock grass 1 Burned - tussock grass 0.8

0.6

of grass bitten of grass 0.4

0.2

0 Proportion Dormant Growing Dormant Growing season season season season 2015 2016 2017 End 70 60 50 40 30 20 10

Dung counts per per month Dungcounts 0 Dormant Growing Dormant Growing season season season season 2015 2016 2017 End

Owen-Smith & Traill 2017 The drought years… Lawn grass Tussock grass 1 Burned - tussock grass 0.8

0.6

of grass bitten of grass 0.4

0.2

0 Proportion Dormant Growing Dormant Growing season season season season 2015 2016 2017 End 70 60 50 40 30 20 10

Dung counts per per month Dungcounts 0 Dormant Growing Dormant Growing season season season season 2015 2016 2017 End Rainfall returns

Lawn grass Tussock grass Burned - tussock grass Lawn grass Tussock grass Burned - tussock grass Lawn grass Tussock grass Burned - tussock grass Decoupling of grazers and lawns

2016 2017 Growing Growing Jan Feb Mar season season 2017 2017 2017

Wheeler et al. 1982 Lawn grass Tussock grass Burned - tussock grass Effect of fire

Community Total tussock Live tussock Dead tussock End of season End of season cover (cm2) cover (cm2) cover (cm2) standing grass standing forb biomass (g.m-2) biomass (g.m-2) Lawn 0 0 0 400 22

Tussock 2699 1589 1110 753 38

Burned 891 106 784 282 82 Summary

1. Tussock grass communities are not always heavily used by grazers during drought events when regional conditions allow for migration to better rainfall areas

2. Grazing lawn systems represent important habitat for grazers even when there is no nutritional benefit

3. Within the Kruger National Park, extreme drought events have the capacity to decouple grazer – grazing lawns feedbacks

4. Burned tussock grasslands were the least productive systems after the drought Thank you

Acknowledgements • • SANParks Robert Bryden • • Working on Fire Tercia Strydom • • Tondani Agnes Tibane Samantha Mabuza References

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