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Fire regimes: Mediterranean Shrublands special attn to Chaparral

This article explores the fire regimes in Mediterranean shrublands, with a special focus on Chaparral. It discusses the different types of Mediterranean shrublands around the world, their adaptations to drought, and the impact of fire on these ecosystems. The article also compares historical and modern fire regimes in California and Baja California, highlighting the factors that influence fire frequency and severity. Implications for fire management and ways to reduce the risk of large fires in chaparral regions are also discussed.

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Fire regimes: Mediterranean Shrublands special attn to Chaparral

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  1. Fire regimes: Mediterranean Shrublandsspecial attn to Chaparral 7 October, 2009 http://www.californiachaparral.com

  2. Mediterranean shrublands • Mediterranean Europe: Southwest France (maquis), Italy (macchia), Spain (tomillares), Balkans (phrygana) • South African – fynbos • South Australia – brigalow scrub • Chile – matorral

  3. Mediterranean Europe • Southwest France (maquis) • Italy (macchia) • Spain (tomillares) • Balkans (phrygana) From: http://bajomartin.wordpress.com

  4. South Africa – Fynbos From: http://www.south-africa-tours-and-travel.com/mountain-zebra-national-park.html

  5. South Australia – Kwongan http://tmwilson.org/gallery/view/gallery/

  6. Chaparral General name for shrublands in western U.S.

  7. 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

  8. 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

  9. 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.

  10. 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?

  11. 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

  12. Keeley & Fotheringham (2000):“Corrected” map of fire occurrence Wildland fires 1972-1980 SoCA & N Baja CA

  13. Why SoCA and Baja CA Chaparral may have different fire regimes?

  14. Precipitation: CA vs. Mexican Chaparral regions

  15. No. of fires and area burned by month: California Chaparral Relationship between population density and fire frequency: CA chaparral

  16. 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!

  17. How different are the modern and historical fire regimes? • Implications of fire regime analysis for fire management?

  18. 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)

  19. 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)

  20. 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)

  21. 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

  22. 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

  23. Chamise, greasewood (Adenostoma fasciculatum, Rosaceae)

  24. Oak shrub

  25. Manzanita (Arctostaphylos sp.)

  26. Grasses Tall shrubs % cover Short shrubs Forbs 0 5 10 15 20 25 Time since fire (years) Post-fire response

  27. 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)?

  28. 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!

  29. 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!

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