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

Recent Burn

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Old burn

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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%

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Results - Species

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% 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

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Recent burn

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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

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Thank you

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