Fire regimes: Mediterranean Shrublands special attn to Chaparral

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

17. 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!

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

19. 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)

20. 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)

21. 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)

22. 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

23. 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

24. Chamise, greasewood (Adenostoma fasciculatum, Rosaceae)

25. Oak shrub

26. Manzanita (Arctostaphylos sp.)

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

28. 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)?

29. 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!

30. 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!