effect of fire and herbivory on tree size transitions in acacia drepanol
TRANSCRIPT
Effects of Fire and Herbivory on Tree Size Transitions in
Acacia drepanolobiumEric M LaMalfa Preliminary data
11/6/2014
Top-down controls on tree cover• Disturbance: Fire AND/OR Herbivory
Are tree size transitions controlled by herbivory x fire?
Tree cover in savannas
Fire effects: •Topkill •Influences plant-plant intxns
- reduced competition for resources
Grazing effects:•Reduces herbaceous biomass•Influences plant-plant intxns
-Reduced competition for1) unpalatable herbaceous plants2) woody plants
Browsing effects•Reduced woody biomass•Reduced seedling establishment•Influences plant-plant intxns
- Reduced competition for herbaceous plants
Direct fire x herbivory intxns• Herbivore preference for burned areas
Increased crude protein content Decreased lignin
Direct fire x herbivory intxns• Grazing reduces fine fuel load/fire continuity
Increased tree survival
• Browsing reduces heavy fuel and fire tempsIncreased tree survival
Indirect fire x herbivory intxnsFire kills tree-obligate ants
Reduced tree fitness
Increased browse pressure
Decreased ant-defense
Laikipia plateau, Kenya • 1800m • Semi-arid 550-600 mm
Cattle Wildife
Mega-herbivores
Acacia drepanolobium• 95% of tree cover • Nitrogen fixing bacteria
nodules• Highly quality (browse and
herbaceous) • Coppices (re-sprouts after fire
and browse damage)
Trees ProvideNest & FoodCrematogaster sjostedt C. mimosaeC. nigricepsTetraponera penzigi
Domatia
Extra Floral Nectary
Ants ProvidePlant Defense
• High defense against herbivores and insects
• High nectar use• High resistance to fire
• Ants track tree resources during sapling colonization• Trees > 1m (grass height) are rarely observed without ants
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?
Experimental Design – Herbivory
• Kenya Long Term Exclosure Experiment (KLEE) • Fences exclude herbivores (since 1995) • Randomized complete block design
W & WC
0 & C
MW & MWC
0= no herbivores
W= wildlife
C= cattle
M= mega-herbivores
MWC
MWC
MWC
MW
MW
MW
W
W
W
C
C
C
0
0
0
WC
WC
WC
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
Post-Fire Trees <1m1
met
er
• 4304 tagged trees • ant sp., tree size, herbivory• % top-kill
Control (no burn)
1 3 5
5 m
30 m
Post fireN = 36 plots27 to 190 trees/ plot1659 trees <1m height
height Main stem length Basal stem length Branch stem length Total stem length Green stem length Main stem diameter Domatia diameterGreen stem diameter Domatia countBasal stem count Green stem count Nectary count (5cm)Ant species
Data
5cm
1m
PRELIMINARY RESULTSHow do fire and herbivory affect small tree (<1m) size transitions?
Un-burned Burned
N = 666 N = 993
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
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
Ant mutualism rewards (nectar)
t = -10.0173, df = 1598.088, p-value < 2.2e-16
12 31
t = -7.5473, df = 1654.985, p-value = 7.295e-14
0.61 1.24
t = -9.2696, df = 1645.348, p-value < 2.2e-16
1.73 3.33
t = -13.8396, df = 1618.421, p-value < 2.2e-16
0.74 1.33
Preliminary resultsHow do fire and herbivory affect ant colonization of small trees?
Extra Floral Nectary
Un-burned Burned
Green Stem Length
Un-burned Burned
Green Stem Diameter
Nectary Count
Un-burned Burned
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.
Do large top-killed trees produce better nectar rewards?
1 m
eter
Next Steps
Next Steps
Does fire temperature affect tree response?
Low heat > High heatDoes herbivory affect tree response?
Low browse > High browse
ant damage neighbor_tree_1 neighbor_tree_2 neighbor_tree_3 neighbor_tree_4 neighbor_tree_5 neighbor_tree_6 neighbor_ant
Neighbor Data
2m
Next Steps
Does neighbor tree colony affect post fire ant colonization?
Thanks
S.J. and Jessie E. Quinney Foundation
Kari Veblen PhD - AdvisorMellisa Harvey LaMalfa – MutualismVeblen Lab – Rebecca, Kyle, Maike
Correlation matrix
ms_
leng
th
tot_
leng
th
gree
n_le
ngth
mai
n_di
am
dom
atia_
diam
gree
n_di
amdo
mati
a_co
unt
basa
l_co
unt
gree
n_co
unt
nect
ary_
coun
tda
mag
e
height 0.78 0.54 0.13 0.72 0.50 0.07 0.59 -0.14 0.10 0.14 -0.03ms_length 0.56 0.14 0.72 0.55 0.11 0.59 -0.15 0.11 0.16 -0.07tot_length 0.48 0.62 0.54 0.37 0.74 0.36 0.50 0.34 0.08green_length 0.22 0.30 0.50 0.35 0.34 0.80 0.47 0.13main_diam 0.56 0.21 0.67 -0.07 0.25 0.24 0.08domatia_diam 0.36 0.57 0.14 0.28 0.32 0.15green_diam 0.29 0.25 0.52 0.50 0.20domatia_count 0.08 0.33 0.33 0.03basal_count 0.37 0.18 0.19green_count 0.44 0.15nectary_count 0.08