Winter Burning of Grass

Fuels in the ACT

Adam Leavesley, Jennie Mallela, Neil

Cooper and Dylan Kendall

Introduction

La Nina from 2010-2012

Lots of rain brought lots of grass

Phalaris – 9t/ha

Canberra’s surrounded by grass

Parliament House 800km of grassy interface

Fuel management zones

Inner Asset Protection Zone (IAPZ)

Outer Asset Protection Zone (OAPZ)

Strategic Fire Advantage Zone (SFAZ)

Urban-rural interface

IAPZ (Mowed)

OAPZ (Under grazing)

SFAZ Under grazing

Fuel management standards

IAPZ = height <200mm when curing >70%

OAPZ = GFH <35 when curing >70%

SFAZ = GFH <50 when curing >70%

GFH = Grass fuel hazard

GFH = % cover x height (m)

High Fuel Loads...

... and fuel continuity across the landscape

An average of 60 burning days/year

Similar budget to previous years

What if we burn in winter?

Fraser

Mulanggari

Fraser – urban-rural interface

Fraser Primary School

Slashed grass Fire ground

Fraser – burn map

Fraser

Mulanggari

Franklin Early Childhood School

Mulanggari Grasslands

Gungahlin Town Centre

Fraser – urban-rural interface

Phalaris canariensis (exotic pasture species)

Grows in spring (cool season)

4 paddocks

Fuel load measured 23 July 2012

Burnt 22 August 2012

Measured February

Mulanggari Grasslands

Themeda triandra (native)

Grows in summer (warm season)

3 paddocks

Fuel load measured 24 July 2012

Burnt 3 September 2012

Measured February

Study design

Before-After-Control-Impact

Paddocks divided into burnt and unburnt

areas

All areas measured before

Paddocks burnt (impact), and unburnt areas

left (control)

All paddocks measured after

Method

5 x 1m2 plots per replicate (10 plots /paddock)

MEASUREMENTS

Fuel load (t/ha)

Fuel moisture content (% dry weight)

Grass height

Grass cover (%)

Grass Fuel Hazard = Height (m) x Cover (%)

Method

Cut the grass one paddock at a time (10 plots)

Collect grass curing, cover and height

Weigh grass at CSIRO

Dry at 105°C for 24 hours (Matthews, 2010)

Weigh again

Analysis

Distribution

Kolgomorov-Smirnov test

Differences

ANOVA (normal)

Wilcoxon signed ranks (non-normal)

Correlation

Pearsons (normal)

Spearmans (non-normal)

Distribution

Fuel load (Z = 0.9, p = 0.4)

Fuel moisture content (Z = 0.9, p = 0.3)

Curing (Z = 1.4, p = 0.04)

Grass height (Z = 1.2, p = 0.1)

Grass fuel hazard (Z = 1.2, p = 0.1)

All normally distributed except for Curing

Before – Fuel load

0

2

4

6

8

10

12

14

16

18

B U B U B U B U

Bravo Charlie Delta Echo

Oven

-dri

ed

Weig

ht

(t.h

a-1

)

0

2

4

6

8

10

12

14

16

18

B U B U B U

Alpha Bravo CharlieO

ve

n D

rie

d W

eig

ht

(t.h

a-1

)

Pasture grass (Phalaris) Native grass (Themeda)

Before – Fuel moisture content

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U B U

Bravo Charlie Delta Echo

Fu

el M

ois

ture

Co

nte

nt

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U

Alpha Bravo CharlieF

ue

l M

ois

ture

Co

nte

nt

Pasture grass (Phalaris) Native grass (Themeda)

Before – Curing

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U B U

Bravo Charlie Delta Echo

Cu

rin

g

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U

Alpha Bravo CharlieC

uri

ng

Pasture grass (Phalaris) Native grass (Themeda)

Before – Height

0

100

200

300

400

500

600

700

B U B U B U B U

Bravo Charlie Delta Echo

He

igh

t (m

m)

0

100

200

300

400

500

600

700

B U B U B U

Alpha Bravo CharlieH

eig

ht

(mm

)

Pasture grass (Phalaris) Native grass (Themeda)

Before – Grass fuel hazard

0

10

20

30

40

50

60

70

80

90

100

B U B U B U B U

Bravo Charlie Delta Echo

Gra

ss F

uel H

azard

Pasture grass (Phalaris) Native grass (Themeda)

0

10

20

30

40

50

60

70

80

90

100

B U B U B U

Alpha Bravo CharlieG

rass

Fu

el H

azar

d

Before - summary

The experimental units of the same species

were not different

There were differences between species

Phalaris at Fraser Themeda at Mulanggari

Impact - Fraser

Burnt 22 August 2012

Impact - Mulangarri

Burnt 3 September 2012

After - Fraser

Residue and regrowth 37 days after the burn

After - Mulanggari

Regrowth 30 days after the burn

Alpha sector control

After – fuel load

0

2

4

6

8

10

12

14

16

18

B U B U B U B U

Bravo Charlie Delta Echo

Ove

n-d

rie

d W

eig

ht

(t.h

a-1

)

0

2

4

6

8

10

12

14

16

18

B U B U B U

Alpha Bravo CharlieO

ve

n D

rie

d W

eig

ht

(t.h

a-1

) (P < 0.001)

Pasture grass (Phalaris) Native grass (Themeda)

After – fuel moisture content

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U B U

Bravo Charlie Delta Echo

Fu

el M

ois

ture

Co

nte

nt

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U

Alpha Bravo CharlieF

ue

l M

os

itu

re C

on

ten

t

Pasture grass (Phalaris) Native grass (Themeda)

After – grass curing

(P < 0.001)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U

Alpha Bravo CharlieC

uri

ng

Treatment required when curing >70%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

B U B U B U B U

Bravo Charlie Delta Echo

Cu

rin

g

Treatment required when curing >70%

Pasture grass (Phalaris) Native grass (Themeda)

After – grass height

(P < 0.001) 0

100

200

300

400

500

600

700

B U B U B U B U

Bravo Charlie Delta Echo

He

igh

t (m

m)

IAPZ fuel standard = 200mm

0

100

200

300

400

500

600

700

B U B U B U

Alpha Bravo Charlie

He

igh

t (m

m)

Pasture grass (Phalaris) Native grass (Themeda)

After – grass fuel hazard

(P < 0.001) 0

10

20

30

40

50

60

70

80

90

100

B U B U B U B U

Bravo Charlie Delta Echo

Gra

ss

Fu

el H

aza

rd

0

10

20

30

40

50

60

70

80

90

100

B U B U B U

Alpha Bravo Charlie

Gra

ss F

uel H

azard

Grass Fuel Hazard

Standards

OAPZ ≤ 35

Pasture grass (Phalaris) Native grass (Themeda)

Summary

It works...

Late-winter/early spring burning:

1) Met the fuel management standards for OAPZ and

SFAZ

2) Met the IAPZ standards in native grass

3) Marginally failed the IAPZ standards in Phalaris

Correlations

Question:

How do the observations compare to the

measurements?

Correlations

Fraser - Phalaris

(r = 0.7, N = 80, p <0.001)

Mulanggari - Themeda

(r = 0.9, N = 60, p <0.001)

Fuel load and GFH

Correlations

Fraser - Phalaris

(r = 0.7, N = 80, p <0.001)

Mulanggari - Themeda

(r = 0.9, N = 60, p <0.001)

Fuel load and GFH

Correlations

Fraser - Phalaris

(Rs = -0.6, N = 80, p <0.001)

Mulanggari - Themeda

(Rs = 0.3, N = 80, p = 0.007)

Correlations

Fraser - Phalaris

(r = 0.7, N = 80, p <0.001)

Fuel load and GFH

Correlations

Mulanggari - Themeda

(r = 0.9, N = 60, p <0.001)

Fuel load and GFH

Summary

1) Themeda fuel loads can be as high as Phalaris even

though they don’t look it.

2) The FMC of Themeda is not necessarily well

represented by curing.

Acknowledgements

Thanks to:

CSIRO Bushfire Dynamics for use of the kiln and helpful

discussions.

My colleagues in the fire crews for all the cutting and

burning.