Climate change, fire, insects, and disturbance interactions: adaptation challenges in the West

Transcription

1 Climate change, fire, insects, and disturbance interactions: adaptation challenges in the West W Climate Impacts Group Don McKenzie Pacific Wildland Fire Sciences Lab U.S. Forest Service

2 Hypotheses about ecosystem change in the West Increasing moisture limits will alter (tree and other) species composition and productivity by locally favoring more xeric species. exacerbating episodes of vegetation dieback. altering mortality and turnover rates. Underlying ecological mechanism = large-scale shift to a negative water balance. Disturbance will be the principal agent of ecosystem change Late 20th-century trends such as increasing insect mortality or fire area burned may be replaced by more abrupt changes. Disturbance interactions produce complex nonlinear behavior, operate at multiple scales, and may be constrained by physical limits. Western Mountain Initiative (WMI) 2008

3 Disturbance drives ecosystem changes Climatic change warmer temperatures more severe and extended droughts New fire regimes More frequent fire More extreme events Greater area burned Fire resets succession, temporal scale associated with fire rotation. The disturbance pathway is quicker Mature trees buffer against effects of warmer climate, temporal scale associated with species longevity. Habitat changes Broad-scale homogeneity Truncated succession Loss of forest cover Loss of refugia Fire-adapted species Much of the same logic applies to insect outbreaks Species responses Fire-sensitive species Annuals & weedy species Specialists with restricted ranges Deciduous and sprouting species

4 Climate and fire area burned, : an ecologically based study in the American West Generalized linear models to scale area-burned statistics to ecoprovinces. Predictive models of fire area burned based on climatology. Potential for ecologically meaningful future projections. Littell et al. (2008)

5 At the scale of ecoprovinces Fuel moisture associated with current climate is the limiting factor. Fuel abundance and continuity associated with previous climate is the limiting factor.

6 Northern mountain provinces, regional fire episodes, and climatic change As temperature increases, the atmosphere evaporates more water from the landscape and plant tissues. MODIS This produces larger than normal areas of depleted fuel moisture during the fire season. Regional synchronization of fires occurs. Northern Rockies, July 2003

7 Arid Southwestern provinces, regional fire synchrony, and climatic change Increasingly severe and prolonged droughts are expected. But interannual cycles, e.g., ENSO, can maintain the pattern of fuel continuity. Invasives like cheatgrass and buffelgrass could change everything.

8 Rapid climatic change may send ecosystems across disturbance thresholds For example Drastic increase in fire severity Mountain pine beetle Doubling of insect reproductive cycles Pandora moth

9 Why temperature increase releases mountain pine beetle populations Population synchronized by temperature (onset of spring). Rate of generation turnover increases with temperature increase. Mountains were a barrier until recently; limitation is now forest extent and continuity. Figure courtesy Allan Carroll

10 MPB outbreaks in high-elevation whitebark pine Railroad Ridge, ID Eastern WA Photo by J. Logan July 2005, Railroad Ridge, ID Quickbird Satellite Imagery

11 Threshold behavior is complex For example If insect population cycles are not synchronized with seasons, outbreaks are not likely. Mountain pine beetle Pinus contorta (lodgepole pine) Hicke et al., J. Geophys. Res.-Biogeosciences, 2006

12 But challenges for adaptation are at the landscape scale Yosemite NP fires >40 ha and <40 ha Yellowstone NP fires and mountain pine beetle Severity Lutz 2008 Simard 2008

13 Patch structures from mixed-severity fire Tripod fire, north-central Washington, 2006

14 Stress complexes: synergistic effects on ecosystems McKenzie, D., D.L. Peterson, & J.S. Littell. In press. Global warming and stress complexes in forests of western North America. In Forest Fires and Air Pollution Issues, eds. A. Bytnerowicz, M. Arbaugh, C. Andersen, & A. Riebau. Elsevier Science, Ltd.

15 Mixed conifer (Sierra Nevada, southern California) Ozone and particulate pollution Fire exclusion high stand densities Extended warm period insects Ponderosa pine, Jeffrey pine, white fir die Fuels accumulate severe fires Exotic plants increase where fires do occur.

16 Global warming Higher temperatures & more severe and extended droughts Sierra Nevada mixed conifer Fire exclusion Ozone Bark beetles and defoliators High stand densities Fuel accumulation Ponderosa and Jeffrey pine mortality Large severe fires Changes in species composition (including exotics)

17 Global warming Higher temperatures & more severe and extended droughts Sierra Nevada mixed conifer Fire exclusion Ozone Disturbance interactions are central but not the only factor. Bark beetles and defoliators Ponderosa and Jeffrey pine mortality High stand densities Fuel accumulation Large severe fires Changes in species composition (including exotics)

18 Lodgepole pine Extended warm period, insects, pines die, fuels accumulate, sets up for large fires. Vulnerable age classes.

19 Interior lodgepole pine Global warming Higher temperatures & more severe and extended droughts Stand-replacing fire regime Bark beetles and defoliators Extensive mature cohorts (70-80 yrs) Lodgepole pine mortality Large severe fires Fuel accumulation Salvage logging Changes in species composition (including exotics)

20 Interior lodgepole pine Global warming Higher temperatures & more severe and extended droughts Stand-replacing fire regime Here too: note context of standreplacing fire. Bark beetles and defoliators Lodgepole pine mortality Large severe fires Extensive mature cohorts (70-80 yrs) Fuel accumulation Salvage logging Changes in species composition (including exotics)

21 Disturbance interactions Timing of wildfires and insect outbreaks can produce positive or negative feedbacks. Thresholds can be reached via cumulative effects or one big event. Spatial pattern matters.

22 Adaptation strategies Connie Millar Nate Stephenson Scott Stephens Ecol. Appl. 17: , 2007 Create resistance to change Promote resilience to change Enable forests to respond to change

23 Increasing precipitation Energy-limited ecosystems (high-elevation forests) Adaptation options change as global warming continues Resistance Resilience Responding? Water-limited ecosystems (eastside & low-elevation westside forests) Increasing temperature

24 Adaptation strategies Anticipate big surprises Expect mega-droughts, larger fires, vegetation dieback, species extirpations, etc. Incorporate these expectations in planning. CCSP 2008

25 Empirical work, synthesis, and modeling to inform adaptation (WMI )

26 Stehekin Lake McDonald RHESSys watersheds Coupled modeling of mountain hydrology, forest vegetation, and disturbance Merced River Frijolito Snake River

27 Thanks! Craig Allen Allan Carroll Ellen Eberhardt Jeff Hicke Jeremy Littell Jim Lutz Connie Millar Dave Peterson Martin Simard Scott Stephens Nate Stephenson (anyone I forgot)