How do marula trees respond to elephant browsing? Rob Taylor, Peter - - PowerPoint PPT Presentation

How do marula trees respond to elephant browsing?

Rob Taylor, Peter Scogings & Dave Ward

Elephants

• Important non-ruminants that consume woody plants in

African savannas

• Little is known of the plant-level responses to elephant

damage

• long-term sever browsing is reported to simulate the

production of nutritious material

• Positive feedback loop

Marula tree

• Prominent savanna tree
• Deciduous, dioecious, and

has high tannin conc. in its’ bark and compound leaves

• Favoured by elephants
• Elephant damage affects

tree growth and survival

How marula trees respond to elephant browsing is important for the sustainable management

• f both these iconic

species and the savanna habitats in which they

• ccur.

Aim

To investigate the relationships between the intensity of browsing attributed to elephants and;

• shoot length
• leaf size
• leaf chemistry
• nitrogen
• condensed tannin conc.

at different canopy positions on male and female marula trees

Methods

• 70 trees in Hluhluwe-

iMfolozi Park

• Control – Hilltop camp
• All remaining trees at

two nearby sites

• High density of both marula

trees and elephants

• Mature trees were sampled (mean height 7.5 m)
• Elephants mostly forage below 5 m
• % of the canopy below the browse line removed by

elephants was recorded

• Tree height
• Tree sex

From below and above the browse line and from damaged and undamaged branches

• Current season shoot growth
• Leaf size
• Tannin & nitrogen concentration

Browsing intensity (%)

20 40 60 80 100 120

N concentration (%)

2 3 4 5 1

Condensed tannin conc. (mg ml

• 1)

1 10 100 Male Female

• Female trees had higher

condensed tannins that male trees

• Condensed tannins

decreased with and increase in browsing intensity

• Above a browsing

intensity of ~60% the nitrogen conc. increased

Leaf size (leaflets leaf-1)

4 6 8 10 12 14 16

Unbroken Unbroken Broken branches, branches, branches, upper canopy low er canopy low er canopy Specific leaf area (cm2 g-1)

40 60 80 100 120 140 160 180 200 220

Shoot length (mm)

50 100 150 200 250 300

• Shoots on broken branches

were longer than on shoots on unbroken branches

• Leaflets were more abundant

per leaf on broken branches than

• n unbroken branches
• Specific leaf area was higher

below the browse line than above

• Specific leaf area was higher on

broken branches than on unbroken branches

Shoot length (mm)

20 40 60 80 100 120 140

Condensed tannin conc. (mg ml

• 1)

10 20 30 40

Specific leaf area (cm2 g-1)

40 60 80 100 120 140 160 180

Condensed tannin conc. (mg ml

• 1)
• 10

10 20 30 40

• Scatter plots of the

relationship between condensed tannins and either shoot length or specific leaf area revealed triangular distributions.

Conclusions

• Female trees had condensed

tannin conc. yet there was no difference in the elephant browsing intensity between sexes

• The strongest chemical responses

to browsing occurred in the most severely browsed trees.

• The strongest growth responses
• ccurred on the damaged branches.
• Compensatory growth occurred

both among trees and within trees.

• Shoot growth may increase under

frequent browsing but long-term browsing may not be beneficial to the plant nor sustainable.

• Further monitoring of the effects of

long term browsing is needed.

• Further research is needed to

validate an approach to managing elephant densities such that reproductive marula trees are not severely browsed.