The effects of rainfall, elephant and fire on woody height class distributions in South African savannas Georgette Lagendijk & Rob Slotow
Amarula Elephant Research Programme, University of KwaZulu-Natal
Introduction
Concern for the loss of trees within African savannas
Are size classes missing from the savanna?
Disruption of ‘natural’ tree size distribution, or population dynamics
Three main ecological drivers: rainfall, fire and herbivory Introduction
Fire-trap <3m Browsing trap, seedlings and saplings
Fire and herbivory intrinsic to savannas BUT
Active management Introduction
Are disruptions in size distributions recruitment or mortality related? Study Area
Kruger National Park Makalali Madikwe Mkuze Pilanesberg Pongola Phinda
Rainfall: 450 – 764 mm
Elephant: 0.13 – 0.68 km2
Fire: 2.5 – 71.7 years
Height classes
Seedling: ≤ 0.5 m Sapling: 0.5-1.5 m Small tree: 1.5-3.0 m Medium tree: 3.0-5.0 m Large tree: ≥ 5.0 m Results ( & discussion)
Positive Negative Rainfall seedlings large trees saplings
Elephant - seedlings medium trees large trees
Fire seedlings - (longer fire medium trees return interval) large trees Results Indicator species
Prolonged fire period (+): Combretum apiculatum, Grewia monticola
Rainfall (+): Acacia nilotica, Euclea natalensis
Elephant (-): Peltophorum africanum
No sign models for Pappea capensis or Ziziphus mucronata
Results Kruger National Park
Missing size classes: medium (3-5 m) large (≥ 5.0 m) trees Conclusion
Disruptions in size classes appear mortality related: elephant and fire
Affecting transition of individual trees through different size classes
Whether this is detrimental to population dynamics and thus the persistance of (specific) species, requires urgent attention
Thank you!
Management of Kruger National Park, Madikwe, Pilanesberg, Makalali, Phinda, Mkuze and Pongola, Bruce Page, Craig Packer, Dave Druce, Matt Repton, Lisette Moolman, Tenjiwe Ndlovu, Sven Bourquin, Debbie Donkin, Dehn von Ahlenveld, Audrey Delsink, Navashni Govender, Pieter Nel, Simon Naylor, Dr. Heinz Kohrs, Heike Zitzer , and UKZN students
Funding: Amarula Elephant Research Programme National Research Foundation University of KwaZulu-Natal