Altered Fire Regime Reduced Montane Forest Diversity. Saupra 1984

Transcription

1 Altered Fire Regime Reduced Montane Forest Diversity Saupra 1984

2 High-severity fire regime? 1997 Rhemtulla et al. 2002

3 Or otherwise? 1997 Rhemtulla et al Bridgland 1924

4 Ecosystem-specific questions How severe and frequent were historic fires? How has fire history affected forest structure and composition? Why has the historic fire regime changed during the 20 th century?

5 0 10 Km

6 Detailed fire history sites (n = 29) 0 2 Km 0 10 Km

7 Detailed fire history sites (n = 29) 0 Fire-years 2 Km S. Kinney

8 Number of trees Evidence of mixed-severity fires through time 15 Fire years Cohort initiation year Veterans Calendar year Tree: lodgepole pine Douglas-fir hybrid spruce trembling aspen

9 Number of trees Mixed- versus high-severity fire histories Mixed-severity (n = 18 sites) High-severity (n = 11 sites) Calendar year Calendar year

10 Lower-severity fires: Fire-scar record Scars at 20 of 29 sites For 11 sites with multiple scars: Fire intervals = yrs, mean return interval = 60 yrs

11 Moderate- to high-severity fires: Cohorts 1 post-fire cohort at all 29 sites Cohorts at 17 sites after fires in 1827, 1889 and 1905

12 Historic mixed-severity fire regime Scars + cohorts = variable fire frequency and severity Contrasts the traditional paradigm that high-severity fires dominate in the Canadian Cordillera

13 Historic mixed-severity fire regime Lack of fire after 1905 is unprecedented

14 pine fir spruce pine fir spruce Canopy IV How has fire history affected forest structure, composition and dynamics? Regardless of fire history, canopy composition was mixed Pine, fir, spruce co-establish after low-high severity fires 200 Mixed-severity (n = 18) High-severity (n = 11) We cannot differentiate mixed- vs high-severity fire history from canopy composition.

15 pine fir spruce pine fir spruce Subcanopy IV Canopy IV How has fire history affected forest structure, composition and dynamics? Regardless of fire history, canopy composition was mixed All subcanopies were strongly dominated by spruce 200 Mixed-severity (n = 18) High-severity (n = 11)

16 Number of trees How has fire history affected forest structure, composition and dynamics? All subcanopies were strongly dominated by spruce Despite small size, similar in age as canopy trees Mixed-severity fire history High-severity fire history Calendar year Tree: lodgepole pine Douglas-fir hybrid spruce trembling aspen Subcanopy spruce persist in absence of fire and form ladder fuels increasing fire hazard

17 Why has the fire regime changed? 0 2 Km

18 Why has the fire regime changed? 5 surface fires no scars 0 2 Km

19 Fires-scar record: 18 fires from No fires after 1915 yet 45 sites with fire-scarred trees Why? Two hypotheses: climate or human impacts 172 Sample depth (n) & No fire scars 2012 Calendar year 1880s-1900s

20 Relationship Correlation coeff i cients Local Douglas-fir: drought indicator Douglas-fir chronology ring widthstree (tree rings) rings Wide Narrow Calendar year Douglas-fir tree rings vs. heat-moisture ( ) Climate-growth analysis A M J J A S O N D J F M A M J J A S Growing season (prior) Winter (prior) Growing season (current) M o n t h a n d s e a s o n r e l a t i v e t o r i n g f o r m a t i o n Negative relationship Good drought indicator

21 Fires burned during droughts Mean index value during fire years versus simulated confidence intervals 18 fires from 1646 to 1915 Negative indices = narrow rings Narrow rings = dry conditions

22 Climate versus human impacts? 20 th C climate was conducive to fire, yet no scars Human impacts Fire years exceeded Drought climate years controls to explain lack of fires Glenbow Alberta Museum & Archives Jasper Yellowhead Museum & Archives Lena Ouellet Coulson

23 1915 Explaining the altered fire regime: Homogenized stands and landscapes 1997 Bridgland 1924 Rhemtulla et al. 2002

24 Explaining the altered fire regime: Homogenized stands and landscapes Strong evidence of historic mixed-severity fire regime Detailed reconstructions needed to differentiate mixedand high-severity fire histories Lack of fires over 20 th C: shifted forest composition and structure increased fire hazard within stands Human impacts exceeded climate to control 20 th C fire Homogenized landscapes and reduced forest resilience

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26 Thank you for your attention Acknowledgments Parks Canada Healthy Landscapes Program at fri Research Hinton Wood Products (West Fraser Mills) Alberta Newsprint Company Natural Sciences & Engineering Research Council of Canada Tree-Ring Laboratory at the University of British Columbia Musqueam First Nation & UBC Faculty of Forestry

27 Fire history and homesteading

28 Correlation Coefficients Local Douglas-fir: drought indicator 0.4 Precipitation Maximum temperature Heat-moisture index A M J J A S O N D J F M A M J J A S Summer (prior) Winter (prior) Summer (current) Month and Season Relative to Ring Formation

29 Climate versus human impacts 20 th C climate was conducive to fire, yet no scars Fire exclusion suppression explain lack of fires Fire years Drought years Glenbow Alberta Museum & Archives Jasper Yellowhead Museum & Archives Coulson Lena Ouellet

30 Fires burned during droughts Drought years associated with El Niños & positive mode of Pacific North American pattern