Fire ecology of ponderosa pine

1. Fire ecology of ponderosa pine • Historically, fires were frequent (every 2-25 yr) and predominantly nonlethal • Droughts are common • Biomass production exceeds decomposition • Ignition is not limiting: lightning and people

3. People have long used warm, dry forests • Indians peeled and ate the inner bark from this tree • Forests were homes, a source of food for people and animals, and many sites were culturally important • Euro-Americans logged, grazed, and mined these forests

4. Biodiversity • Ponderosa pine forests provide habitat for many animals (at least 250 species of vertebrates), plants, invertebrates, and microbes • Many rare, sensitive and declining species, e.g. northern goshawk and flammulated owl • Habitat alteration and fragmentation affects invertebrates and soil organisms that are critical to ecosystem function.

5. Ponderosa pine forests are shaped by: • Frequent surface fires • Episodes of tree regeneration • Insect infestations • Regional climatic events, such as droughts • Human use

6. Fire effects on trees • Crown damage • Foliage dies if crown burns (needles black or gone) • Scorch (red needles) is caused by dessication • PIPO can survive up to 75% crown scorch • Cambium damage • Bole and roots • Look for pale green, moist inner bark • Tree can survive damage on up to 50% of circumference

8. Fire effects • Fires consume biomass and recycle nutrients • Fires rejuvenate vegetation • Fires influence diversity • Many plants and animals depend on the forest structures and composition that develops post-fire

10. Fire exclusion • Fire suppression • Roads • Valley settlements • Fewer Indians (many died of introduced diseases after first white contact); many moved to reservations • Very intensive grazing – in the Southwest grazing was used to prevent fires

11. Fire exclusion • When was the last surface fire that scarred this tree? • What was the average number of years between fires that scarred this tree? • This is from Long Valley near Flagstaff, Arizona, an area where fires were once VERY frequent

12. Forest structure has changed • Fewer large trees and snags – these are ecologically, economically, and socially more important than small trees • More trees that are less fire resistant • Unnaturally dense stands of suppressed young trees now threaten the remaining large trees through competition and by fueling crown fires

14. Ecosystem composition changes • Old-growth is rare • Meadows have shrunk • Many native plants and animals have declined in abundance due to habitat alterations

15. An “outbreak” of Douglas-fir • In some stands, white fir, Douglas-fire, and juniper have increased

16. Fuels accumulate when fires are less frequent • Fuels accumulate on the forest floor (as duff, litter, woody debris) and in the crowns of trees • Increased crown fuel loading • Fuels are more continuous horizontally • Fuels are more continuous vertically • Fire size and intensity increases • Crown fires are more likely

17. Changed ecosystem processes • Decreased tree growth • Trees are less vigorous • Organic matter decomposition slows • Nitrogen mineralization declines • Stagnant nutrient cycles • Declining diversity of native flora and fauna • Increased risk of stand-replacing fire

18. Spatial patterns have changed • Simpler patterns and processes at all hierarchical levels, from stand to landscape • Stands are less aesthetically pleasing • Landscapes are more homogeneous • Greater canopy closure

19. Watershed effects • Decreased water availability • Decreased total streamflows, peak flows, and base flows • Post-fire erosion and mass-wasting increases when fires are more severe

20. Increasing fire risk • Dramatically increased vulnerability of warm, dry forests to destructive crown fires • Threatening people, property, watersheds and wildlife habitat • More than 39 million acres at risk to catastrophic fires (GAO 1999) in US – much is in the warm, dry forests

21. Human actions have made these forests less sustainable • Fire suppression • Livestock grazing • Logging, especially of bigger trees and pines • Road construction • Predator control • Exotic species introductions

22. Many have called for active management • To reduce fire risk, restore ecosystem health, and to protect people and their property • Some combination of thinning “from below” (taking smallest trees only) and prescribed burning

23. Visualizing alternatives: the next six slides • Simulation and visualization using Fire Fuels Extension of the Forest Vegetation Simulator • Ponderosa Pine State Park near McCall, Idaho – they have thinned and burned to reduce fuel risk around visitor center, campgrounds and other recreation sites

30. Examples • Fuels management efforts under the National Fire plan • Ecological restoration

31. National Fire Plan • More money for fire fighting, fire rehabilitation, fuels management, community assistance and accountability • Especially in urban/interface and in municipal watersheds • Much of the attention is focused on warm, dry forests, including ponderosa pine • Read the 2002 overview: http://www.fireplan.gov/ • Skim the Western Governor’s Association Implementation Strategy: http://www.westgov.org/wga/initiatives/fire/implem_plan.pdf

32. Fuels management prescriptions • Probably, fewer trees need to be cut to reduce the risk of crown fires than to do ecological restoration • It should be a goal for both to enhance sustainability and resilience of ecosystems

33. Prescribed fire programs • The scale and intensity of Rx fire programs are inadequate at a regional scale.

34. The call for restoration

35. Restoration • Strong consensus that need exists • Heated public and scientific debates about the relative risks and tradeoffs of different approaches

36. Ecological restoration • Reintroduce fire • Thin trees from below • Reduce tree densities, especially small trees • Reestablish understory vegetation • Alter forest structures: increase spatial heterogeneity

37. One approach and a critique • Continue with this powerpoint for an overview • Then continue with the case study to see more about this approach, critiques of it, and alternatives, as well as ongoing research

38. Reference conditions • Covington, Moore, Fulé and others at the Ecological Restoration Institute at Northern Arizona University • Substantial efforts to reconstruct and reestablish the tree density and spatial pattern that existed just prior to the date of cessation of the natural fire regime • Test the effects of treatments on ecosystem components • Restore surface fires

39. Strengths of this approach • Clear methods • Readily quantifiable • Scientifically based • Concrete

40. Challenges to the approach • Intensive – many trees are cut at once • Integrates structure, but what about composition and ecosystem processes? • Need an adaptable method • Because of lagged response of forest structure to climate variation, the precise replication of past plant densities and spatial arrangements may not maximize future ecosystem resilience • Post-settlement tree regeneration pulses would occurred to some degree

41. Multiple incremental treatments are an alternative • A search for ecological integrity and sustainability for the future • Addresses these issues • Any particular moment in time may be unique in the long-term history of an ecosystem • Climate of the late 20th century is unprecedented in last 1,000 years

42. Multiple incremental treatments • Use a combination of thinning and fire • Thin only enough to allow prescribed fire • More conservative and justifiable • Potentially allows more extensive treatments • Identify thresholds where fire alone will be enough

43. Successful restoration projects • Address issues: natural heterogeneity, wildlife and biodiversity • Accommodate our imperfect understanding of these complex systems • Require political, financial, and social support • Scientifically sound

44. Principles of ecological restoration of Southwestern ponderosa pine forests (from Allen et al. In Press) • Reduce vulnerability to crown fires • Integrate process and structure • Site-specific reference conditions • Multiple conservative interventions • Build upon existing forest structure • Restore ecosystem composition • Retain trees of significant size or age

45. More principles • Incorporate demographic processes • Control and avoid introducing exotics • Protect and enhance sensitive communities and regional heterogeneity • Prioritize treatment areas Consider cumulative effects • Protect from overgrazing • Monitor and do research • Use ongoing adaptive management in a diversity of approaches

46. More principles • Retain some dead, deformed and diseased trees • Keep some clumps of large trees with interlocking crowns • Maintain important food and nesting habitat • Maintain genetic diversity • Use opportunities to increase habitat heterogeneity and biodiversity

47. Other considerations • Pay attention to vulnerable and irreplaceable ecosystem elements • Leave some areas untreated as refuges for sensitive species • Adjust future treatments • Maintain future flexibility • Avoid creating uniform stand and landscape conditions

48. Given uncertainties, act conservatively • Limited understanding of ecosystem function • We know more about past fire frequency than about past fire size, severity, and spatial pattern • Uncertain reconstruction of fire regimes and past structure and composition due to missing evidence and sampling bias • Use reconstructed overstory tree densities conservatively (as minimum rather than maximum values)

49. Goal • Move toward natural range of variability • Allow or use natural processes, such as fire, to reestablish natural structure and function