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 abrahamdabengwa@gmail.com XIX INQUA Congress 26 July - 2 August, 2015, Nagoya

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?

Climate and vegetation Importance of climate in shaping vegetation

Climate and vegetation Topography soils elevation etch

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

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

Ecological disturbance and vegetation Catastrophic change…fire deforestation disease,

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

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

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

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

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

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

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

Vegetation change

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

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

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

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

Disturbance

Fire

Role of fire

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

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

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?

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)

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

Thank you!

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: http://books.google.co.za/books?id=hzNmAAAAMAAJ. 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: http://linkinghub.elsevier.com/retrieve/pii/S0305440308002896 (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), e0124202, Available from: http://dx.plos.org/10.1371/journal.pone.0124202.