Ecohydrologic mechanisms of
Mopane in the Kruger National Park
Jesse B Nippert & Anthony M Swemmer
photo: AK Knapp
Predicting the FUTURE…
Savanna types and distributions are susceptible to climate change
because temperature and rainfall are key drivers of this ecosystem.
Changes may impact latitudinal ranges of varying savanna types
Climate and soil processes are not deterministic for savanna
distribution: interplay of local site drivers and evolutionary history is key.
National Parks provide a refugia for
species, but with global change the
distribution of species / ecosystem
types within parks is likely to
change.
Environmental gradient in KNP
provides a novel platform to assess
tradeoffs between water use, flux
and drought tolerance among
species and savanna types.
Biology of Colophospermum mopane
Mopane savanna typically has lower alpha and beta diversity than Acacia /
Combretum savanna
Mopane savanna covers ~ 500,000 km2 across southern Africa, with tree
density ranging between 2-5,000 individuals/ha
Irregularly drought deciduous species
Commonly found on heavy soils across wide gradients of nutrient
availability
Classified as drought tolerant, and yet water limitation is the most common
limiting resource for growth.
Roots concentrated in surface soils, but high lateral branching and
taproots common.
We know lots about belowground form / biology, but we know comparatively little
about ecological differences in water consumption, transport, and flux vary in
relation to coexisting dominant species (e.g., Acacia nigrescens, Combretum
apiculatum)
Historical dynamics
Paleo-ecological evidence suggests that Mopane savanna size
is dynamic over time (past 700 years).
Mopane pollen abundance is highest during dry-cool climate
periods, lowest during wet-warm. The forecast dry-warm
climate represents a no-analog environmental condition.
Gillson and Ekblom 2010 Landscape Ecol. Anecdotal
evidence over the
20th century
suggests Mopane
is getting denser,
suggesting direct
or indirect
correlations with
modern climate
changes
A dynamic modern ecotone
Photo: Alan Knapp
Questions (Q1) Does the physiology/morphology of Mopane provide an
ecohydrological advantage compared to other savanna tree
species, either by quickly utilizing available soil moisture or by
being the most drought tolerant species?
(Q2) How do source-water dynamics vary between Mopane
and the other common KNP savannah species?
(Q3) Can we use spatial environmental gradients in Southern
Africa to predict savanna productivity, water flux, and cover,
both now and in the future?
Sample collection
Source-water samples:
2009 – Ecotone south of Olyphants River
2011 – Malopeni
Leaf carbon isotopes
2011 – Phalaborwa Gate to Mopani Camp
Leaf gas exchange – stem morphology
2011 – Malopeni, near Phalaborwa Gate.
Basalt PM
A / C ecotone Mopane
18
O (
‰)
-9
-8
-7
-6
-5
-4
-3
-2
-1
mopane
other tree spp.
Granite PM
Ecosystem-type sampled
A / C ecotone Mopane
18
O (
‰)
-9
-8
-7
-6
-5
-4
-3
-2
-1
mopane
other tree spp.
Basalt PM
During the dry season (winter), Mopane is using water
from deeper in the soil profile than coexisting trees (Euclea divinorum / natalensis, Combretum imberbe / heroense / apiculatum,
Maurea parvifolia, Phylenoptera violocea, Acacia tortillis / nilatica)
Source water differences among
mature Mopane shrubs,
seedlings and grasses. -1‰
-2‰ δ18O
adult -5.6 to -2.9‰
seedling -6.5 to -3.5‰
grass -3.5 to -1.1‰
When wet, Mopane has a higher capacity for water flux
compared to other coexisting species
Jan. 2011 – Phalaborwa
Acacia
exuv
ialis
Acacia
nigr
esce
ns
Cissu
s co
rnifo
lia
Colop
hosp
erm
um m
opan
e
Com
bret
um a
picu
latu
m
Com
bret
um h
erer
oens
e
Com
ifera
afri
cana
Com
rbet
um m
osam
bice
ns
Dalbe
rgia m
elan
oxylon
Dichr
osta
chys
ciner
ea
Euclea
divino
rum
Flueg
gea
viro
sa
Gre
wia b
i-color
Lonc
hoca
rpus
cap
asss
a
Pelto
phor
um a
frica
num
Rhigo
zum
zam
besiac
um
Scler
ocar
ya b
irrea
Term
inalia p
runo
ides
Term
inalia ser
icea
Le
af sa
mp
les -
1
3C
(‰
)
-32
-31
-30
-29
-28
-27
-26
March 2011 – Phalaborwa
Scaling water-source use and flux on the landscape using
allometeric predictions of root mass and rooting depth
~lateral roots to 16m from stem
~tap roots to 3m depth
Mopane
0
5
10
15
20
25
30
35
40
45
0 100 200 300 400
Total basal area of all stems (cm2)
To
tal ro
ot
mass (
kg
)
Conclusions (…so far)
Appears Mopane uses multiple ecohydrologic strategies compared to
co-occurring woody species
Quick consumption and flux of water when surface soils are wet
Utilize deep-soil water with high stomatal regulation when soils are dry to
avoid water stress
A warmer and drier future climate is likely to alter woody species
distributions in KNP, with the potential for Mopane spread further
south.
knobthorn Mopane
Proposed Next Steps
Greater source-water sampling
More detailed analysis of structural traits among species
Physiological and morphological
Assessment of plant responses to varying site factors
Acknowledgements
NSF-LTER Nature Conservancy Division of Biology
K-State Eco-Phys Lab
Teall Culbertson, Jeff Hartman, Gracie Orozco,
Troy Ocheltree, Zak Ratajczak
Alan Knapp Gene Kelly
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