Post on 26-Apr-2018
transcript
THE EFFECTS OF SPORADIC FIRE ON WOODY
VEGETATION DENSITY, COVER AND STRUCTURE
AT TIISA KALAHARI RANCH – BURNING
CONTRASTS
Edwin Mudongo, Richard Fynn
Methods
• Location – Ghanzi
ranches (western
Botswana)
• Semi-arid climate
• Sampling (May 2012) : 2
fence-lines
– Recent burn (1yr)
– Old burn (6yrs)
– Paired transect sampling
– Recent burn = 16 pairs
– Old burn = 18 pairs
– 10m from fence
2
0 50 10025 Kilometers
Legend
Study Site Fence
! Town / Settlement
Pan
District Boundary
Other Roads
Fenced Ranches
Game Reserve
Wildlife Management Area
Main Road
±
!
!
!
Barnes Oasis Ranch
Tiisa Ranch GH10
GH 1
CKGR
GantsiGhanzi
Hanahai Hills
Okwa
Okwa
Grootlaagte
Results – Recent Burn
Variable Burnt Unburnt Effect size (95%CI) t statistic P - value
ln % Canopy cover 2.9 3.4 0.45 (-0.02 – 0.9 ) 2.06 0.058
ln height (m) 0.1 0.4 0.30 (0.2 – 0.5) 4.38 0.001
ln density (trees.ha-1) 8.0 8.2 0.18 (-0.25 – 0.6) 0.89 0.39
No. of species 5.5 5.81 0.31 (-0.76 – 1.4) 0.62 0.55
ln stems per plant 5.25 5.35 0.11 (-0.4 – 0.6) 0.45 0.66
ln no. >20 stemmed
plants
1.4 0.8 0.55 (-0.22 – 1.3) 1.53 0.15
Shannon-Wiener Index
(H')
1.96 1.94 0.68 (-0.36 – 1.7) 1.39 0.18
Jaccard Index 85%
Results - Old burn
Variable Burnt Unburnt Effect Size
(95%CI)
t statistic P - value
% Canopy cover 42.50 38.44 4.05 (-6.7 – 14.8) 0.79 0.439
Height (m) 0.87 1.10 0.22 (0.1 – 0.3) 3.82 0.001
ln density
(trees.ha-1)
7.9 7.7 0.15 (-0.2 – 0.5) 0.87 0.39
No. of species 4.11 4.00 0.11 (-0.6 – 0.87) 0.31 0.762
Stems per plant 150 141 8.9 (-48 – 68.9) 0.33 0.75
No. >20 stemmed
plants
5.7 5.4 0.28 (-1.3 – 1.9) 0.36 0.72
Shannon-Wiener
Index (H')
1.79 1.73 0.65 (-0.91 – 2.21) 0.89 0.39
Jaccard Index 67%
6
Results - Species
7
% Canopy cover Height (m) Density (tree. ha -1)
Species Burnt Unburnt P-value Burnt Unburnt P-value Burnt Unburnt P-value
T. camphoratus 0.69 3.18 0.047 0.11 0.80 0.007 11.1 83.3 0.005
A. erioloba 2.44 2.51 0.969 0.13 0.79 0.112 150.0 172.2 0.910
A. hebeclada 7.31 3.30 0.180 0.60 0.21 0.045 100.0 44.4 0.037
A. mellifera 4.68 4.55 0.954 0.59 0.63 0.815 450.0 455.6 0.973
A. nebrownii 1.25 2.54 0.486 0.25 0.15 0.488 155.6 222.2 0.704
B. albitrunca 0.00 0.00 0.331 0.00 0.02 0.331 0.0 11.1 0.331
C. alexandrii 3.94 4.41 0.707 0.15 0.27 0.830 1627.8 1388.9 0.533
C. hereroense 1.47 0.54 0.279 0.50 0.22 0.201 61.1 61.1 1.000
Commiphora spp 0.00 0.01 0.331 0.00 0.02 0.331 0.0 5.6 0.331
E. rigida 0.00 0.03 0.331 0.00 0.02 0.331 0.0 27.8 0.331
G. flava 17.64 17.20 0.864 1.15 1.24 0.254 472.2 505.6 0.754
G. heterophylla 0.01 0.00 0.331 0.06 0.00 0.331 5.6 0.0 0.331
G. retinervis 0.01 0.00 0.338 0.01 0.00 0.533 5.6 5.6 1.000
R. brevispinosum 0.03 0.00 0.191 0.07 0.00 0.214 27.8 0.0 0.172
Results – multiple stems (recent burn)
Species Burnt Unburnt Effect size
(95%CI)
t statistic P-value
G. flava 1.94 1 0.94 (-0.24 - 2.11) 1.70 0.11
A. hebeclada 0.31 0.06 0.25 (-0.16 - 0.66) 1.29 0.22
C. alexandrii 1.44 0.81 0.63 (-2.12 - 3.37) 0.49 0.63
C. hereroense 0.12 0.25 0.13 (-0.26 - 0.51) 0.70 0.50
R. brevispinosum 0.73 0 0.73 (-0.56 - 2.03) 1.21 0.25
A. mellifera 0.5 0 0.5 (0.11 - 0.89) 2.74 0.02
8
Conclusions
• Cover, density and height of T.
camphoratus reduced by fire
• For most spps only height reduced
• Follow-up fires may help maintain shorter
state woodland for browsers
• Result supported by other studies –
generally only structure reduced by fire
10