Fire ecology of ponderosa pine

Transcription

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

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3 People have long used warm, dry forests Fire Ecology - FOR526 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 Fire Ecology - FOR526

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

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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

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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

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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

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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: Skim the Western Governor s Association Implementation Strategy: ves/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 longterm history of an ecosystem Climate of the late 20 th 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

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