1. 1.) Is there a big tree effect in the Kruger National Park
savanna?
2.) What is the effect of burn intensity on the big tree
effect, or how does it affect the woody plant
communities around big trees?
3.) How accurate is Light Detecting and Ranging
(LIDAR) for collecting tree demographic data?
Results
Mathew Pattillo, Ryan Suttle, Alejandro de la Torre, Aaron Weerasinghe
Introduction
Methods
Keeping it Cool Cool: Effect of Fire Intensity and Big Trees on
Understory Woody Plant Communities in Kruger National Park
Discussion
Acknowledgements
References
Background
The co-existence of large trees with other woody plants and grasses is
crucial to the maintenance of the savanna biome (Archer 1988). Big trees,
such as Marula trees (Sclerocarya birrea) act as nutrient hotspots,
facilitating understory growth (Belsky et at. 1989). This phenomenon is
known as the “big tree effect.”
Large tree populations have been declining in Kruger National Park,
partially due to increasing elephant populations. The resulting increased
bark-stripping leaves trees vulnerable to fire damage, particularly xylem
and cambium damage (Midgley et al. 2010).
Firestorm Experiments
Over a period of five years, SANParks conducted firestorm experiments in
the Skukuza land type of Kruger National Park to address the issue of
homogeneity of fire regimes. Prior to these experiments, controlled burns
were done according to the 30-30-30 rule: burning on days over 30%
humidity, under 30ºC, and under wind speeds of 30 km/h. As part of the
firestorm experiment, areas were burned at high or low intensities, and then
burned again two years later. The Hot Hot (HH) plots were burned twice at
high intensity and the Cool Cool (CC) plots were burned twice at low
intensity, with time of year determining intensity. The data suggest that HH
plots experienced a 35% decrease in big tree populations compared to a 3%
decrease in the CC plots (L. Kruger pers. comm.).
Belsky, A. J., R. G. Amundson, J. M. Duxbury, S. J. Riha, A. R. Ali, and S. M.
Mwonga. 1989. The Effects of Trees on Their Physical, Chemical and Biological
Environments in a Semi-Arid Savanna in Kenya. Journal of Applied Ecology 26 (3):
1005-1024.
Ludwig, F., H. de Kroon, H. H. T. Prins, and F. Berendse. 2001. Effects of nutrients and
shade on tree-grass interactions in an East African savanna. Journal of Vegetation
Science 12: 579-588.
Devine, A.P., I. Stott, R. A. McDonald, and I. M . D. Maclean. 2015. Woody cover in
wet and dry African savannas after six decades of experimental fires. Journal of
Ecology: 1-6.
Koch, B., U. Heyder, and H. Welnacker. 2006. Detection of Individual Tree Crowns in
Airborne Lidar Data. Photogrammetric Engineering & Remote Sensing 72 (4): 357-
363.
Midgley, J. J., M. J. Lawes, and S. Chamaill é-Jammes. 2010. Savanna woody plant
dynamics: the role of fire and herbivory separately and synergistically. Australian
Journal of Botany 58: 1-11.
Moncrieff, G. R., L. M. Kruger, and J. J. Midgley. 2008. Stem mortality of Acacia
nigrescens induced by the synergistic effects of elephants and fire in Kruger National
Park, South Africa. Journal of Tropical Ecology 24 (16): 655-662
Statistica. 2011. Version 10.0. Statsoft, Inc., Tulsa, Oklahoma, USA.
Is there a big tree effect in the Kruger National Park
savanna?
We assessed the biomass and species richness of the
understory woody plant communities of Marula trees to
understand how the big tree effect manifests.
• Collected stem diameters from each individual plant
within five meters of the base of Marula trees
• Control plots free from influence of big trees taken
from at least 25 meters away
What is the effect of burn intensity on the big tree
effect?
We collected data from both the HH plots and the CC
plots in the same manner to understand the effect of
burn intensity on the big tree effect.
• Bark stripping, borer damage, and fire damage data
were collected to create tree mortality narratives
How useful and accurate is Light Detecting and
Ranging (LIDAR) for collecting tree demographic
data?
• Any tree over 10 meters we found not tagged by
LIDAR was tagged manually to evaluate the
effectiveness of LIDAR at identifying trees.
We would like to thank our resource mentors Laurence Kruger and
Immanuel Zwane for their contributions to our study. We would also like to
thank Julia Boyer for her contributions to our data, our game guard Phillip
Mhlava for his assistance, and Kruger National Park for allowing us to
conduct our research.
Conclusions
• The big tree effect is prominent in this system and increasing burn
intensity dampens the effect.
• Biomass and biodiversity was higher both under living trees and in the
CC site.
• Only one CC tree showed visible signs of fire damage vs. 12 HH trees
• Tree mortality narrative for most trees, both CC and HH, was
toppling after massive borer damage
• We suggest CC trees suffered less fire damage and therefore less xylem
and cambium damage
• The difference in biomass between fire intensities may be due to the
persistence of the big trees in CC sites. Trees in the CC site suffered
less damage from fire and could continue fostering understory
growth.
• Fire managers should consider burning at lower intensities to preserve
big trees, thus preserving woody plant communities.
• LIDAR is acceptably accurate and will produce a realistic
distribution of living to dead trees
The greatest difference in biomass was found between
total CC trees and total HH trees (t=2.285, df=35,
p=0.0284). Greater biomass was found in living CC
tree plots than in their respective control plots
(t= -1.673, df=22, p=0.108).
Diversity of woody plant communities was highest in
plots collected around living CC trees, and was lowest
in living HH tree controls. Total HH tree plots and
total HH control plots had the largest difference in
biodiversity (t=2.970, df=36, p=.005).
Green area indicates CC plots
Yellow area indicates HH plots
Questions