Fire regimes in the fynbos biome: Is there cause for concern? Brian van Wilgen CSIR Natural Resources and Centre for Invasion Biology

Fire regimes in the fynbos biome: Is there cause for concern?

Brian van WilgenCSIR Natural Resources andCentre for Invasion Biology

© CSIR 2006 www.csir.co.za

Topics covered

• What are fire regimes?

• What is the concern?

• What evidence is there to support the concern?

• What are the consequences of altered fire regimes?

• What should be done about this?

• Ideas for research


What is a fire regime?Concept first proposed by Gill (1975)

• Frequency – return period (1/yr)

• Season – summer, winter, spring, autumn; wet season, dry season

• Intensity –rate of energy release

• Type – surface, crown, ground

• Severity – measure of impact on ecosystems

• Size – the size distribution of individual fires

• Variability – in all of the above in successive fires


What is the fire regime in the fynbos biome?

• KNOWN• Fires every 10 – 15 years, in summer or early autumn, of

moderate intensity (5000 – 10 000 kW/m)

• Severity affected by invasion by alien plants which increase fuel loads

• NOT KNOWN• Fire size distributions altered by fragmentation, fire control

and prescribed burning

• Degree of variability that can be tolerated


Appropriate and inappropriate fire regimes

Altered fire regimes can be: Ecologically acceptable (still able to maintain

plant and animal populations) Ecologically unacceptable (species are lost)

Current “wisdom” - Fires in winter, fires that are too frequent (< every 8 years), or too infrequent (> every 35 -40 years) are inappropriate


Fire regimes as surrogate measures for biodiversity

• First proposed by van Wilgen, Richardson & Seydack (1994)

• The achievement of biodiversity goals too complex to monitor

• Diversity in fire regimes (within limits) should be easier to monitor, and could act as a surrogate measure for biodiversity


What are the major concerns around fire regimes?

• Fires may be becoming too frequent as a result of increased sources of ignition

• Habitat fragmentation and fire control means that historic (appropriate?) fire patterns do not establish

• Invasion by alien plants increases fire severity• Climate change may alter fire regimes in future, making

them inappropriate• Our inability to control fires impacts on benefit streams (eg

flower harvesting)• Fires cost us bags of money


Measuring fire regimes - Swartboskloof catchment example


1995

1985

1980

1990

1975

10 yrs

5 yrs 15 yrs

Calculating fire return periodsCalculating fire return periods


Cumulative probability of fire at SwartboskloofCumulative probability of fire at Swartboskloof

Pro

bib

ilit

y o

f fi

re

Time since last fire (yrs)

0

1

30

..5

16



What evidence is there to support the main concerns?

• Fire frequency assessed from fire records, remote sensing, or people’s memories or perceptions

• Each has problems

• Most reliable evidence is for fire severity associated with alien plant invasions

• Very little known about fire patterns, or the costs of fires


KAMMANASSIE

0

20

40

60

80

100

0 5 10 15 20 25 30 35

TIME SINCE LAST FIRE (years)

CU

MA

LA

TIV

E A

RE

A (

ha)

< 60% of area burnt at age < 7 years



Richardson andvan Wilgen 1984SA Forestry Journal

Cover down 1/3 Species down 50%

Holmes et al. 2002(Austral Ecology)

Some important guilds missing



Business day article


The main economic costs of fires

• Total losses: R750 million per year• Forestry and downstream industries: R250 • Livestock losses R150• Alien plant control in fynbos R100

• Costs of fire control: R70 million per year

• This kind of analysis does not consider the value or loss of biodiversity


Cost of houses lost in fires not known, butrelatively small


Unplanned fires in invaded areas may be costing a great deal

• Unplanned fires - additional follow-up.

• The 4.3 million ha fynbos burns once in 15 years

• Roughly 286 000 ha burns every year.

• 33% invaded to some degree

• CapeNature estimated additional costs at R1000 per ha.

• Assuming 100 000 invaded ha burns in unplanned fires every year, additional costs around R100 million annually.


What would constitute an unacceptable fire regime?

• Too much area that burns too frequently (or in the wrong season) too often.

• How much is too much?

• How often is too often?

• The key seems to be to define the amount of variability that can be tolerated – “thresholds of potential concern”


The origin of thresholds of potential concern• From savanna ecology –

shift from “balance of nature” to “flux of nature”; and stable-state to a heterogeneity paradigm

19401940 19501950 19601960 19701970 19801980 19901990

Rain

fall

Rain

fall




What evidence is there that we can influence or control fire regimes?

• Very few no attempts to quantify this – two from South Africa

CEDERBERG: Fire Records 1956-1986. “... effects of prescribed burning (introduced in 1973) on the extent and frequency of wildfires are not yet evident.”

KRUGER PARK: Fire Records 1941-1996. “the probability of a fire of any size occurring is principally a function of grass biomass.”


1957 – 1975 Fixed-cycle burning1980 – 1990 Flexible-cycle burning1990 – 2002 Lightning fires


Effects of management on the extent of fires in the Kruger

National Park

Effects of management on the extent of fires in the Kruger

National Park

1100

1100

Fixed Burning

Are

a bu

rned

(ha

x 1

000

)

Mean rainfall in preceding 2 years (mm)

100 300 500 700 900 1100

200

1000

400

600

800

0

All Fires

100 300 500 700 900 1100

200

1000

400

600

800

0

Flexible Burning

100 300 500 700 900

200

1000

400

600

800

0

Lightning

100 300 500 700 900

200

1000

400

600

800

0


The concept of adaptive management

• Set goals based on current understanding

• Monitor achievement of goals against thresholds of potential concern

• If thresholds exceeded, intervene, or re-set the threshold

• This is hard work, not a cop-out!

• We need long-term monitoring to inform us.


Max age

Median fire return period

Min age

0 10 20 30

0.5

1

Post-fire age (years)

Pro

port

ion b

urn

t

THRESHOLDS OF POTENTIAL CONCERN IN FYNBOS

THRESHOLDS OF POTENTIAL CONCERN IN FYNBOS


What are the consequences of altered fire regimes or an inability to control fires?

• Loss of species and ecosystem stability (biodiversity)

• Spread of alien plants (impact on water resources and catchment stability; or increased control costs)

• Loss of property, crops (forestry big, houses small)

• Tourism?


Do we have the capacity to practice good fire management?

Catchment management system (published in 1994 in International Journal of Wildland Fire)

National Fire Danger Rating System

Capacity (and willingness to risk) prescribed burning

Working on Fire – genuine attempt to gain control, but no mandate; staff turnover


Some questions for research• Ecological research – variability in fire regimes and their

impacts. Long-term monitoring sites and simulation models.

• Fire regime research – develop thresholds of potential concern, and implement effective monitoring

• Management – integrated control of invasive plants; effective models for intervention (suppression and prescribed burning)

• Economic research – cost of fires, and returns on investment from management (control and suppression vs other forms of management)

• Climate change?


Thank you

Documents

Fire regimes in the fynbos biome: Is there cause for concern? Brian van Wilgen CSIR Natural Resources and Centre for Invasion Biology