Fire regimes: Mediterranean Shrublands

special attn to Chaparral

7 October, 2009

http://www.californiachaparral.com

Mediterranean shrublands • Mediterranean Europe: Southwest France (maquis),

Italy (macchia), Spain (tomillares), Balkans (phrygana)• South African – fynbos• South Australia – brigalow scrub• Chile – matorral

Mediterranean Europe

• Southwest France (maquis)

• Italy (macchia)• Spain

(tomillares)• Balkans

(phrygana)

From: http://bajomartin.wordpress.com

South Africa – Fynbos

From: http://www.south-africa-tours-and-travel.com/mountain-zebra-national-park.html

South Australia – Kwongan

http://tmwilson.org/gallery/view/gallery/

ChaparralGeneral name for shrublands in western U.S.

Common to all Mediterranean Shrublands

• Mediterranean climate– hot, dry summers– cool, moist winters

• Shrub dominated vegetation

• Leathery (sclerophyllous) leaves with thick cuticles, thick bark: adaptations to drought

• Recurrent fire

Chaparral communities - Arizona

• Shrub-like oak and other shrub species

• Between ponderosa pine and desert grasslands in elevation

• Takes ~20 years for fuel to build up enough for fire (which occurs during droughts)

• Fire every ~50-100 years

Chaparral communities - California

• Many different shrub communities referred to as Chaparral:– “Chaparral”: woody,

drought-hardy shrubs. – “Soft chaparral” or “Sage

scrub”: sage, romatic semi-woody, and semi-deciduous drought-tolerant shrubs.

– “Hop-sage shrubland”: low-growing and arid.

California Chaparral• Mediterranean climate• Santa Ana winds• Convection storms & lightning• Topography: steep• Soils:

– Moderately fertile– Water repellent

• Vegetation:– High shrub biomass– Dense stands of contiguous fuels

• What is the historic fire regime? How can this be determined?

SoCA vs Baja CA (Mex)hypothesized historical & modern fire regime(Minnich 1983):

• Historical (pre-fire suppression): frequent, small fires produced fragmented landscape of different age classes, then large fires are not frequent.

• Modern: Fire suppression homogenizes landscape, then large, severe “un-natural” fires are more frequent.

Wildland fires

1972-1980

SoCA & N Baja CA

Keeley & Fotheringham

(2000):

“Corrected” map of fire occurrence

Wildland fires

1972-1980

SoCA & N Baja CA

Why SoCA and Baja CA Chaparral may have different

fire regimes?Group Who?

1 Difference in fire frequency Sydney, Scott Cressler, Sean

2 Comparability of fire climates Tyler, Jason, Bianca

3 Factors affecting fuel production Scott B., Alyssa, Sondra, Blake

4 Landscape features and Patterns of land use

Cody, Kiley, Brittany

5 Proposed Modern fire regime Daniel, Maggie, Darren, Lucas

6 Proposed Historical fire regime Evan, Kelly, Angela

Precipitation: CA vs. Mexican Chaparral regions

No. of fires and area burned by month:

California Chaparral

Relationship between population density and fire frequency: CA chaparral

Summary: Fire regimes in BajaCal and SoCal are likely different because…

• Greater human ignitions due to land use (= more frequent fires)

• Mexico lacks the strong Santa Ana winds; weaker on-shore NW breezes (= smaller fires)

• Slower fuel accumulation rates in Mexico due to lower rainfall and poor soils (= affects rate of spread (ROS) and burning patterns)

• Mexico lacks the steep & rugged topography (= affects fuel production, ROS)

But not because of fire suppression!

• How different are the modern and historical fire regimes?

• Implications of fire regime analysis for fire management?

Historic fire regime in CA Chaparral• Fire (mostly) dictated by weather

– Drought determines when fires burn provided there is ignition– Fire equally likely for all ages after 20 years (Moritz et al. 2004).

• Season:– Lightening-ignited fires in July and August– Most summer fires small but can burn for months

• Severity and Intensity– Stand-replacing crown fires – Variable intensity

• “Hold over fires” – in logs/humus - can ignite into large fires by the Santa Ana winds in

September (100 km/h, burn >30,000 ha in one day!)

• Average fire return interval: ~ 70 years (highly variable: coast vs. interior; lightening frequency; range: <5 to > 100 years)

Contemporary fire regime in CA Chaparral

• Frequency– increased over historical range due to the “human

subsidy”– average fire-return interval: 30-40 years

• Severity:– Same (Stand-replacing)

• Season– Same (summer – fall)

• Scale / Extent– Same (Landscape)

“ contemporary fire regime …mirrors the natural fire regime far more closely than is generally credited” Keeley & Fortheringham (2000)

Implications for Fire management

• Fire suppression efforts effective to reduce large catastrophic fires?

• Prescribed fire/fuel reduction efforts?

• What is the best approach for managing fire risk in the WUI in Chaparral regions?

From: Morrtz et al. (2004)

Implications for Fire management, cont.

• Large fires are largely the result of anthropogenic ignitions: potentially preventable!– restrictions on use of machinery in wildland

areas during severe fire weather– Power lines underground Santa Ana winds

corridor

Land use zoning and community planning

Fire ecology of CA chaparral• Evergreen shrubs with small, leathery (sclerophyllous) thick

leaves

• Many shrubs are known to resprout following fire (remember lignotubers) – Chamise (resprouter)– Shrub oaks (resprout)

• But, some don’t– Manzanita (some resprout, some don’t)– Variety of sub-dominant shrub species

• All species produce seeds; need fire scarification

• Leaves often contain highly flammable oils

Chamise, greasewood (Adenostoma fasciculatum, Rosaceae)

Oak shrub

Manzanita (Arctostaphylos sp.)

Post-fire response

% cover

Time since fire (years)

0 5 10 15 20 25Forbs

Grasses

Short shrubs

Tall shrubs

TTYP

• What is the dominant vegetation at 1, 5, 10, 25 years since fire? Why for each?

• What might happen if fire is excluded for long periods of time?

and, if fire is too frequent (< 5 year return interval)?

Fire exclusion

• If fire excluded, succession to taller and more diverse plant communities.

• But after 20 years old, fire risk is high for all chaparral communities.

• REMEMBER: driven more by extreme fire weather than by age and spatial patterns of fuels.

Succession to tall forests unlikely!

Increases in Fire Frequency

• Some shrub species can resprout (only older individuals die)

• Non-sprouters rely on seed production• Repeated fires and non-sprouters?• What replaces them?

– Fire resilient grasses (largely exotic, invasive species)

Driving large-scale vegetation-type conversion that is more prone to fire!