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