1. Effects of Fire and Herbivory
on Tree Size Transitions in
Acacia drepanolobium
Eric M LaMalfa
Preliminary data
11/6/2014

2. Tree cover in savannas
Top-down controls on tree cover
• Disturbance: Fire AND/OR Herbivory
Are tree size transitions controlled by herbivory x fire?

3. Fire effects:
•Topkill
•Influences plant-plant intxns
- reduced competition for resources

4. Grazing effects:
•Reduces herbaceous biomass
•Influences plant-plant intxns
- Reduced competition for
1) unpalatable herbaceous plants
2) woody plants

5. Browsing effects
•Reduced woody biomass
•Reduced seedling establishment
•Influences plant-plant intxns
- Reduced competition for herbaceous
plants

6. Direct fire x herbivory intxns
• Herbivore preference for burned areas
 Increased crude protein content
 Decreased lignin

7. Direct fire x herbivory intxns
• Grazing reduces fine fuel load/fire continuity
Increased tree survival
• Browsing reduces heavy fuel and fire temps
Increased tree survival

8. Indirect fire x herbivory intxns
Fire kills tree-obligate ants
Decreased ant-defense
Increased browse pressure
Reduced tree fitness

9. Laikipia plateau, Kenya
• 1800m
• Semi-arid 550-600 mm
Cattle
Wildife
Mega-herbivores

10. Acacia
drepanolobium
• 95% of tree cover
• Nitrogen fixing bacteria
nodules
• Highly quality (browse and
herbaceous)
• Coppices (re-sprouts after fire
and browse damage)

11. Trees Provide
Nest & Food
Crematogaster sjostedt
C. mimosae
C. nigriceps
Tetraponera penzigi
Extra Floral
Nectary
Domatia
Ants Provide
Plant Defense
• High defense against herbivores
and insects
• High nectar use
• High resistance to fire

12. • Ants track tree resources during sapling colonization
• Trees > 1m (grass height) are rarely observed without ants

13. Research Questions
1) How do fire and herbivory affect small tree (<1m)
size transitions?
2) How do fire and herbivory affect ant colonization
of small trees?

14. Experimental Design – Herbivory
• Kenya Long Term Exclosure Experiment (KLEE)
• Fences exclude herbivores (since 1995)
• Randomized complete block design
MW & MWC
W & WC
0 & C
C= cattle
W= wildlife
M= mega-herbivores
0= no herbivores
MWC
MWC
MW
MW
MWC
MW
W
W
W
C
C
C
0
0
0
WC
WC
WC

15. Experimental Design – Fire
• 18 burns, February 2013
• 12 treatments, 3 replicates
• 4304 tagged trees
• ant sp., tree size, herbivory
• % top-kill
Kimuyu D.M., Sensenig R.L., Riginos C., Veblen K.E., and T.P. Young (2014). “Native and domestic browsers and grazers reduce fuels,
fire temperatures, and acacia ant mortality in an African savanna.” Ecological Applications 24(4): 741–749

16. Post-Fire Trees <1m
1 meter
• 4304 tagged trees
• ant sp., tree size, herbivory
• % top-kill

17. Control (no burn)
1 3 5
5 m
30 m
Post fire
N = 36 plots
27 to 190 trees/ plot
1659 trees <1m height

18. height
Main stem length
Basal stem length
Branch stem length
Total stem length
Green stem length
Main stem diameter
Domatia diameter
Green stem diameter
Domatia count
Basal stem count
Green stem count
Nectary count (5cm)
Ant species
Data
5cm

19. PRELIMINARY RESULTS
How do fire and herbivory affect small
tree (<1m) size transitions?
1m
Un-burned Burned
N = 666 N = 993

20. 5cm
Tree size (<1m)
39 25 233 254
t = -1.6733,
df = 1292.361,
p-value = 0.09451
t = 16.1482,
df = 1013.013,
p-value < 2.2e-16
Tree Height Total Stem Length

21. Ant mutualism rewards (domatia)
t = 3.2196,
df = 1000.367,
p-value = 0.001325
9.95 7.63
t = -1.7532,
df = 1255.261,
p-value = 0.07981
9.9 10.5

22. Ant mutualism rewards (nectar)
0.61 1.24
t = -7.5473,
df = 1654.985,
p-value = 7.295e-14
12 31
t = -10.0173,
df = 1598.088,
p-value < 2.2e-16
0.74 1.33
t = -13.8396,
df = 1618.421,
p-value < 2.2e-16
1.73 3.33
t = -9.2696,
df = 1645.348,
p-value < 2.2e-16

23. Preliminary results
How do fire and herbivory affect ant
colonization of small trees?
Extra Floral Nectary

24. Green Stem Length
Un-burned Burned

25. Green Stem Diameter
Un-burned Burned

26. Nectary Count
Un-burned Burned

27. Conclusions
1. Mean tree size in the <1m size class is
no different 1.5 years following fire.
2. Ant mutualism traits associated with
nectar are higher in burned trees.
3. After fire, small trees occupied by C.
nigriceps (BBR) and C. mimosae (RRB)
& have higher nectar rewards.

28. Do large top-killed trees produce
better nectar rewards?
1 meter
Next Steps

29. Next Steps
Does fire temperature affect tree response?
Low heat > High heat
Does herbivory affect tree response?
Low browse > High browse

30. Next Steps
Does neighbor tree colony affect post fire
ant colonization?
Neighbor Data
ant
damage
neighbor_tree_1
neighbor_tree_2
neighbor_tree_3
neighbor_tree_4
neighbor_tree_5
neighbor_tree_6
neighbor_ant
2m

31. Thanks
S.J. and Jessie E.
Quinney
Foundation
Kari Veblen PhD - Advisor
Mellisa Harvey LaMalfa – Mutualism
Veblen Lab – Rebecca, Kyle, Maike

32. Correlation matrix
ms_length
tot_length
green_length
main_diam
domatia_diam
green_diam
domatia_count
basal_count
green_count
nectary_count
damage
height 0.78 0.54 0.13 0.72 0.50 0.07 0.59 -0.14 0.10 0.14 -0.03
ms_length 0.56 0.14 0.72 0.55 0.11 0.59 -0.15 0.11 0.16 -0.07
tot_length 0.48 0.62 0.54 0.37 0.74 0.36 0.50 0.34 0.08
green_length 0.22 0.30 0.50 0.35 0.34 0.80 0.47 0.13
main_diam 0.56 0.21 0.67 -0.07 0.25 0.24 0.08
domatia_diam 0.36 0.57 0.14 0.28 0.32 0.15
green_diam 0.29 0.25 0.52 0.50 0.20
domatia_count 0.08 0.33 0.33 0.03
basal_count 0.37 0.18 0.19
green_count 0.44 0.15
nectary_count 0.08