A contrast of the woody
communities and plant traits inside
and outside of three long term
exclosures in Kruger National Park
BJ Wigley; H.Fritz; WJ Bond
Laboratoire de Biométrie et Biologie Évolutive
UMR CNRS 5558
Browsers and woody plant interactions
in savannas
• Community composition & spp. distribution(e.g. Bond
and Loffell, 2003)
• Population structure and size class distributions
(Pellew, 1983; Augustine and McNaughton, 2004)
• Tree abundance affects savanna dynamics (tree
grass interactions, nutrient cycling, etc.)
• Selective feeding related to food quality (Owen-Smith &
Cooper 1987)
i.e. certain species are targeted
• Impact on recruitment and interactions with fire
also NB (Augustine and McNaughton, 1998, 2004; Staver et al. 2009)
Most studies species specific – elephants prime
suspects
• Marula, Sclerocarya birrea (Coetzee et al., 1979; Gadd, 2002 and
Helm & Witkowski, 2012)
• Knobthorn, Acacia nigrescens (Fornara & Du Toit, 2007; Moncrieff
et al., 2011)
• Mopane, Colophospermum mopane (Styles & Skinner, 2000; Smallie
& O’Connor, 2000)
• Baobab, Adansonia digitata (Edkins et al., 2008)
• These studies informative as they have
improved our understanding of their
autecology.
• Don’t provide a better understanding
of savanna dynamics at the
community level.
• Need for replicated experiments that
assess the effects of native browsers
on shrub dynamics in African savannas
• “Our understanding of the importance
of browser effects on woody plant
dynamics remains unclear” (Augustine and
McNaughton, 2004).
• Setting up of manipulative experiments
difficult and expensive
• Luckily in Kruger there are long-term
exclosures (often coincidental)
Study Objectives
•
Determine if there are differences in woody community compositions,
population structures and leaf traits between the woody communities
found growing inside and outside of three long-term exclosures in Kruger
National Park (KNP)
OUTSIDE
INSIDE
Questions addressed
1) Has the long-term exclusion (> 40 years) of
browsers led to differences in woody plant
community compositions at the three exclosures?
2) Do the population structures and abundances of
the woody populations differ inside and outside
of the exclosures?
3) How do plant leaf traits compare between
species only found inside vs. species found
outside?
Study sites
• Nhlangwini exclosure near Pretoriuskop  750
MAP, sandy soils derived from granite.
• Makhohlola exclosure near Crocodile Bridge 
600 MAP, clay soils derived from basalt.
• N'waxitshumbe exclosure on the northern
plains  400 MAP, clay soils derived from
basalt.
Study Sites
Map
Transects
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100 m x 4 m wide transects both inside and outside of exclosures at each site
Species identity, functional type (tree or shrub), height, crown diameter, life
history (seedling, sapling or adult)
Types of browser impact (leaf, twig, branches and bark) and fire impact (stem,
crown, coppicing and topkill) recorded for each woody plant encountered
Made use of a PDA with installed CyberTracker software.
Trait measurements
Trait
Abbreviation
Unit
Leaf nitrogen content
Leaf N
%
Leaf carbon content
Leaf C
%
Leaf phosphorous content
Leaf P
%
Leaf magnesium content
Leaf Ca
Mg kg-1
Leaf calcium content
Leaf Mg
Mg kg-1
Leaf sodium content
Leaf Na
Mg kg-1
Leaf potassium content
Leaf K
%
Specific leaf area
SLA
cm2 g-1
Average leaf area
ALA
cm2
Leaf dry matter content
LDMC
mg g
Leaf tensile strength
TS
N mm-1
Bite size index
BSI
NA
Bark moisture content
Bark moist
%
Stem specific density
Stem density
g cm-3
Total phenolics
TP
%
Condensed tannins
CT
%
Neutral detergent fibre
NDF
%
Acid detergent fibre
ADF
%
Acid detergent lignin
ADL
%
Results - Community compositions
12 spp
13 spp
8 spp
16 spp
10 spp
8 spp
Tree densities
Size class distributions - Nhlangwini
Size class distributions - Makhohlola
Size class distributions - N'waxitshumbe
Leaf traits
Leaf nutrients
Chemical defence
Fibre
Community compositions
• At Nhlangwini higher diversity outside, inside
dominated by Terminalia sericea in small size classes
• At Makhohlola, higher diversity inside, much higher
number of small Acacia nigrescens on the inside
• At N’waxitshumbe equal diversity but different
compositions, Dalbergia melanoxylon common inside
but not found outside, Mopane - more common and
taller inside, none <1m for both treatments
• The results suggest that herbivory has had an impact
on community compositions, population structures
and overall woody plant densities.
Leaf traits
• Leaf N, total phenolic content and lignin
content were the only three traits that
showed consistent patterns between
treatments.
• This strongly suggests that herbivores
preferentially select species with higher leaf N
concentrations, and species with lower total
phenolic and lignin content in leaves
Conclusions
• At the higher rainfall sites, ca. 40 yrs of browser
removal did not result in establishment of
woodland
• Fire has managed to keep the dominant species
trapped in small size classes
• Supports the idea that cohorts of trees recruit
simultaneously , however need a break from both
herbivores and fire
• Maybe we should be worried about the loss of
large trees in the park (not sure when they will be
replaced)
• At the semi-arid site browsers effect on
composition seemed to be most pronounced
• Also seem to be some species that do better
with browsers (e.g. Dic cin and Alb har) more
common outside at all three sites
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Corli Coetsee
Lucas Enrico
Rensin, Vheli, Jacob
SANParks
CNRS
Mellon Foundation
Acknowledgements