1. Abraham Dabengwa, Lindsey Gillson and William Bond
Untangling herbivore fire patterns in human-affected landscapes from a sedimentary fossil record: a case study from KwaZulu-Natal, South Africa
Abraham Dabengwa, Lindsey Gillson and William Bond
XIX INQUA Congress 26 July - 2 August, 2015, Nagoya

2. Aim
To disentangle the effects of fire and herbivore activity from climate on local vegetation change using palaeoecological proxies
Questions:
How did local vegetation isotopic signal respond to known climate events?
What was the role of local ecological disturbance by fire and herbivores in vegetation change? Can these processes be disentangled?

3. Climate and vegetation
Importance of climate in shaping vegetation

4. Climate and vegetation
Topography soils elevation etch

5. Climate and vegetation
LOCAL SCALE
CLIMATE VARIABILITY AFFECTS VEGETATION
SCALE DEPENDENT EFFECTS

6. Ecological disturbance and vegetation
DGVM FIRE OFF
Fire as a “global herbivore”
DGVM FIRE ON
Limits climatic potential of vegetation
(Bond & Keeley 2005)

7. Ecological disturbance and vegetation
Catastrophic change…fire deforestation disease,

8. Ecological disturbance and vegetation
Multiple temporal and spatial scales
Overgrazing fence line contrast

9. Ecological disturbance and vegetation
DOMESTICATED HERBIVORES
MEGA & MESO HERBIVORES
Water dependent
Large social groups

10. Ecological disturbance and vegetation
People and technology
Agricultural revolution
Control of resources
(Bond & Keeley 2005)

11. Attributing local vegetation change
Vegetation change(s) can be due to many causes:
Climate key driver of major changes but some vegetation types are maintained by disturbance
Disturbance drivers can often interact adding layers of complexity (coupling and decoupling)
All the above can affect the resilience of the system
Complexity

12. Study sites Elevation B 950-1200 AD A C B A Rainfall C B A C
AD 400 Iron Age in SA
Phragmites australis, Vachelia sieberiana A C

13. THE PIOSPHERE CONCEPT HERBIVORES FIRE Explain piosphere
Usefulness in understanding megaherbivores
Common problem in reserves and communal areas

14. Riparian local C3
Fire
Herbivores/
Humans
C4 Grassland (Landscape)
C3 Riparian
Core
Major disturbance = drought and deforestation
Herbivores respond to enviro signals
C C3
Disturbance increases permeability of local vegetation signal to C4 landscape signal
Time

15. Vegetation change

16. Vegetation change from δ13C signal in sediment
Landscape C4
Grassland/ Terrestrial signal
Can changes be explained by ecological disturbance? C3
Local

17. Vegetation change from δ13C signal in sediment
Landscape C4
MWP
LIA
Grassland/ Terrestrial signal
Can changes be explained by ecological disturbance? C3
Local

18. Vegetation change from δ13C signal in sediment
Landscape C4
MWP
Mapungubwe Kingdom collapses (Huffman 2009)
LIA
Grassland/ Terrestrial signal
Can changes be explained by ecological disturbance? C3
Local

19. Vegetation change from δ13C signal in sediment
Baobab tree δ13C rainfall proxy for NE South Africa (Woodborne et al. 2015)
Vegetation change from δ13C signal in sediment
Landscape C4
MWP
Mapungubwe Kingdom collapses (Huffman 2009)
LIA
Grassland/ Terrestrial signal
Can changes be explained by ecological disturbance? C3
Local

20. Disturbance

21. Fire

22. Role of fire

23. Herbivore presence
Increased access to basin in dry period = shallow water
More indicative of local conditions than herbivore abundance

24. Role of herbivores
Sporormiella increase associated with vegetation shift from C3 to C4 and conversely
Livestock require pasture/grass but are known to damage vegetation around water sources (piosphere effect)
Common problem in major parks providing water for large herbivores, distorts normal movement and environmental controls
L;ivestock don’t control vegetation

25. Fire and herbivore interaction
Facilitation between fire and herbivory? (↑herbivore access)
Fire activity precedes herbivore activity
Active manipulation of fire, possibly by Nguni herders/ farmers to increase access to riparian fringe?

26. Conclusion Climate is main driver of vegetation
Disturbance regimes interact with climate and each other, in turn coupling and decoupling (anthropogenic influence/ signal???)
Local C3 vegetation was resilient to disturbance (phytolith work will explore this angle)
Herbivore proxies most indicative of local moisture than herbivore abundance in tropics with negative water balances (shallow water→ increased access)
Riparian zones are key resource use areas for animals and humans
Numerical analyses required to test threshold effects and mechanisms (drivers vs responders)

27. Acknowledgments Supervisors: Lindsey and William
INQUA/LOC Travel grant
ACDI
NRF - African Origins Platform
NRF - South African Earth Observation Network
ACCESS
KwaZulu-Natal Wildlife Services (Ezemvelo)
Plant Conservation Unit

28. Thank you!

29. Citations
Bond WJ and Keeley JE (2005) Fire as a global ‘herbivore’: The ecology and evolution of flammable ecosystems. Trends in Ecology and Evolution.
Hall M (1981) Settlement patterns in the Iron Age of Zululand: an ecological interpretation. BAR international series, B.A.R., Available from:
Huffman TN (2009) A cultural proxy for drought: ritual burning in the Iron age of Southern Africa. Journal of Archaeological Science, Elsevier Ltd, 36(4), 991–1005, Available from: (accessed 16 March 2012).
Woodborne S, Hall G, Robertson I, et al. (2015) A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.). Plos One, 10(5), e , Available from: