Bridging the gap; what have we learned from ten years of palaeoecological research in Kruger and Greater Limpopo Park? Lindsey Gillson lindsey.gillson@uct.ac.za Anneli Ekblom anneli.ekblom@arkeologi.uu.se
Why Palaeoecology? Conserving ecosystems in flux requires a knowledge of long-term variability but few data sets cover more than a few decades / the last century, and until recently there has been very little palaeoecological work in the Kruger National Park. This information gap has been partly addressed by studies of fossil pollen, charcoal, stable isotopes, diatoms and dung fungal spores that allow the reconstruction of longterm vegetation change, fire history, climate change, nitrogen availability and herbivore abundance. Funded by the Trapnell Fund and Andrew W. Mellon Foundation Lindsey Gillson, Anneli Ekblom, Kristina Duffin and Elinor Breman all took part in the project - thanks to Bill Robertson and the AW Mellon Foundation. We have published eleven peer-reviewed data papers to date. Here we will focus only on the Kruger Park and PNL work of Ekblom, Gillson and Duffin.
Aim and Approach The aim was to study tree-grass dynamics over long timescales (hundreds thousands of years) in relation to key drivers (Fire, climate, herbivory, and nutrients). Focus on conservation applications, and hypotheses testing based on current theoretical frameworks Emphasis on past-present-future continuum, and links to neo-ecology (NOT traditional Quaternary Science!) We used a multi-proxy approach including fossil pollen, stable isotopes, charcoal abundance, dung fungal spores, and diatoms in a multitude of wetland locations throughout Kruger and Limpopo National Park (PNL) We interpreted our data in terms of: KNP s Strategic Adaptive Management Approach (Thresholds of Potential Concern) Resilience Theory, Scale and Hierarchy Theory
Palaeoecology, Strategic Adaptive Management and TPCs (Gillson and Duffin 2007) Plants produce different amounts of pollen with different dispersal abilities Therefore % pollen abundance is not the same as % abundance of plants We modelled the relationship between arboreal pollen abundance and woody plant cover using modern pollen data and vegetation surveys. This allowed us to convert our fossil pollen data to estimated of woody plant cover...
...Which we could then compare with KNP s Thresholds of Potential Concern: Woody cover should not drop by more than 80% of its highest ever value Difference in maximum estimates highlights importance of sitespecific TPCs Using highest ever is problematic as a benchmark for guiding management TPC based on deviation from the mean or and or co-efficient of variation might provide be more useful? May need different TPCs for preserving grasslands? Mafayeni Malahlapanga
Resilience Theory 1: Variability versus resilience in Riverine Vegetation at Mapimbi (Gillson and Ekblom 2009, Ekblom et al 2011) For most of the past 700 years, the Riverine Gallery Forest at Mapimbi has been sensitive to climate Transition from the medieval warm period ending in the 14th century A.D. to the cooler, drier conditions of the little ice age of ca. A.D.1400 1800. Riverine Gallery Forest benefitted in warmer, wetter periods Riverine forest contracted in Little Ice Age but bounced back quickly (c. hundred years)
Resilience Theory 1: Variability versus resilience in Riverine Vegetation at Mapimbi Significant, anthropogenic influence (maize cultivation and increased local fires) after A.D. 1800 Lowest tree cover was after not coincident with peak in cultivation: probably only small areas were cleared Decline in cultivation occurred in the end of the 20th century linked with changes in sociopolitical organisation An increase in woody cover in recent decades may be associated with the management of the area by Kruger National Park? And / or CO2? Riverine forest may be sensitive to climate change but also resilient in the sense of a relatively quick recovery (decades-centuries)
Resilience 2: Irreversible Transition of Grassland elements at Malahlapanga? (Gillson and Ekblom 2009) The pollen from grasses was bimodally distributed providing evidence of alternate stable states At Malahlapanga, we found evidence of a transition between alternate stables states Charcoal and tree pollen appeared at the same time in the palaeo-record
Resilience 2: Irreversible Transition of Grassland elements at Malahlapanga? We developed a conceptual model that explained a hysteretic (irreversible) transition between open grassland and wooded savanna: Temporary wetter conditions increased grass biomass allowing fire and trees into the system It switched from a herbivore and nutrient limited grassland to a fire and herbivore limited wooded savanna
Resilience, Scale and Hierarchy Theory Gillson 2004
Resilience 3: Resilience and limiting factors at Radio and Chixuludzi Pans Chixuludzi Pan: water-rich as it is connected with a river system Significant correlation between trees (arboreal pollen) and dung spore abundance (herbivory) Significant correlation between trees (arboreal pollen) Nitrogen availability
Resilience 3: Resilience and limiting factors at Radio and Chixuludzi Pans Radio Pan: Water scarce as it is isolated from rivers systems No correlation between Tree cover (Arboreal Pollen) and Fire (charcoal) No correlation between Tree cover and Herbivory (Coprophilous spores) No correlation between Tree cover (Arboreal Pollen) and nitrogen availability (δ 15 N)
2 scenarios in savannas where rainfall is low (c. 600 mm/year) Where local hydrology is constraining water availability determines max abundance of woody cover Other factors (fire, herbivory, nutrients have little or no effect and the grassland is stable Where local hydrology is NOT constraining water availability Other factors (fire, herbivory, nutrients, human activities) influence tree abundance and the vegetation is variable Shows importance of local context (Levick 2008)
Hierarchy and scale (Gillson 2004) (After Gillson 2004) Rainfall is a higher order constraint spatially and temporally. At the local scale, local hydrology, determines ecosystem response to other local variables such as fire, nutrient availability, and herbivory:
Open Questions APPLICATIONS Can TPCs be modified to include local factors? Is the Historical Range of Variability useful as a basis for TPCs? Can Palaeorecord help to identify Early Warning Systems - patterns of variability (e.g. coefficient of variation) that occur before a threshold transition (Wang et al 2012?) and can these be incorporated into TPCs? TPCs for grassy ecosystems may be needed if trends in scrub encroachment increase, fuelled by CO 2 enrichment and increasing temperature (Higgins and Scheiter 2012) What are the implications of the improved rainfall record? (Woodborne et al)
Open Questions THEORY Which is resilient? A variable system like Riparian vegetation, which is sensitive to climatic change but recovers quickly A very stable system like a waterscarce grassland, that changes little because it is constrained by local hydrology. Can hierarchy theory adapt? Scale matters, but scale alone cannot predict dominant processes because of a) local context (Levick et al ) b) overlapping modalities (Barichievy 2012) Alternatives: Does network theory provide a better framework? Can Dobson et al s work include a temporal dimension?
Publications 1. Breman, E., L. Gillson, and K. Willis. (2012). How fire and climate shaped grass-dominated vegetation and forest mosaics in northern South Africa during past millennia. The Holocene 22:1427-1439. 2. Ekblom, A., Gillson, L., Risberg, J., Holmgren, K. & Chidoub, Z. (2012) Rainfall variability and vegetation dynamics of the lower Limpopo Valley, Southern Africa, 500 AD to present. Palaeogeography, Palaeoclimatology, Palaeoecology 363-364, 69-78. 3. Ekblom, A., L. Gillson, and M. Notelid. (2011) A Historical Ecology of the Limpopo and Kruger National Parks and Lower Limpopo Valley Journal of Archaeology and Ancient History 1:1-29. 4. Ekblom, A. and Gillson, L (2010) Fire History and Fire Ecology of northern Kruger (KNP) and Limpopo National Park (PNL), Southern Africa. The Holocene 20: 1063 1077 5. Ekblom, A. and Gillson, L (2010) Hierarchy and Scale: Testing the Role of Water, Grazing and Nitrogen in the Savanna Landscape of Limpopo National Park (Mozambique). Landscape Ecology 25:1529 1546 6. Ekblom, A. & L. Gillson (2010) Dung fungi as indicators of past herbivore abundance, Kruger and Limpopo National Park. Palaeogeography, Palaeoclimatology, Palaeoecology, 296, 14-27. 7. Gillson, L., and A. Ekblom. (2009) Resilience and Thresholds in Savannas: Nitrogen and Fire as Drivers and Responders of Vegetation Transition. Ecosystems 12:1189-1203. 8. Gillson, L. and Ekblom, A. (2009) Untangling anthropogenic and climatic influence on riverine forest in the Kruger National Park, South Africa. Vegetation History and Archaeobotany 18:171-185 9. Duffin, K. I., L. Gillson, and K. J. Willis (2008) Testing the sensitivity of charcoal as an indicator of fire events in savanna environments: quantitative predictions of fire proximity, area and intensity. The Holocene 18: 279-291 10. Duffin, K and Bunting, J. (2008) Relative pollen productivity and fall speed estimates for southern African savanna taxa Vegetation History and Archaeobotany 17:507 525 11. Gillson, L. and Duffin, K. (2007) Thresholds of potential concern as benchmarks in the management of African savannas. Philosophical Transactions of The Royal Society of London B.362: 309-319
Trapnell Fund, Higgins-Trapnell Family Foundation, Scientific Services, SANParks Thank you Mellon Foundation