Tree ring methods & applications to fire ecology of the Rocky Mountains

Transcription

1 Tree ring methods & applications to fire ecology of the Rocky Mountains

2 Xylem transport water and nutrients heartwood dead cells sapwood live cells Phloem living tissue that caries organic nutrients (e.g. sugars) to plant parts as needed). Innermost bark layer Cambium lateral meristem that produces new phloem and xylem Annual rings are in the xylem

3 Annual ring formation

4 Annual ring formation

5 Annual ring formation Vertical Cross Section: stacked cones of annual growth layers age depends on the height of the sample

6 Annual ring formation earlywood latewood Bark

7 Annual ring formation False Ring What would cause a false ring to form?

8 What affects tree ring growth widths?

9 Climatic Influences on the growth of subalpine trees in the Colorado Front Range (Villalbla and Veblen 1994) Permanent Plots near CU Mt Res Station installed in 1982

10 MRS 7: Very Dry MRS 5: Wet Flat, Bog spruce-fir forest South-facing, Open, Limber- Spruce-fir dominated

11 Site MRS 7 DRY Prec. Increases Larger rings temp. increases Smaller rings Response analysis: determine if tree is responding to climate variables

12 Site MRS 5 wet bog Temp. increases Larger rings How does site influence response?

13 What is usually the limiting factor for annual tree growth at lower elevations (e.g. lower montane)?

14 Fire history methods Fire scar dates Age/cohort structure of trees

15 Fire Scar Formation Heat from fire partially kills cambium Live cambium eventually grows over scar Upslope side of tree Fire travels uphill flame tips wrap around tree Fuel accumulation

16 Fire Scar Collection

17 Fire Scar Dating Count from outer ring to fire scar tip Outer ring = sample year Peter Brown

18 Fire Scar Dating Dieterich and Swetnam 1984

19 Fire Scar Data Analysis Date fire scars 2 scars = fire event Calculate mean fire interval (MFI) avg # yrs between fire events for a period of time period Problems with fire scar evidence Loss of evidence (death and fire) MFI dependent on search area Targeted sampling

20 Age Structure Methods Tree cores collected Date tree establishment Graph establishment dates for each site (essentially the age distribution) Single cohort Multi cohort Continuous

21 Combined cohort & fire scar inferred fire severity

22 Forest types and fire history of the Colorado Front Range

23 Outline Fire type spectrum and effects 3 major Rocky Mountain forest types and associated tree species Historic Range of Variability and Federal Legislation Fire history across forest types and variable effects of fire suppression

24 Fire regime Parameters Severity Frequency Size Seasonality Patchiness Fire Regime

25 Fire Severity Fire severity definition: 1. Degree of ecological change 2. Amount of biomass consumption A measure of the ecological effects of fire

26 Low-severity fire

27 Low-severity effects

28 Variable-severity fire

29 Variable-severity effects

30 High-severity fire

31 Regeneration after Yellowstone fires, 1988 High-severity effects M Turner

32 Outline Fire type spectrum and effects 3 major Rocky Mountain forest types and associated tree species Historic Range of Variability and Federal Legislation Fire history across elevations and variable effects of fire suppression

33 Vegetation Types in Boulder County

34 Forest Types in Boulder County Lower Montane Zone ( m) Ponderosa pine (Pinus ponderosa) Douglas fir (Pseudotsuga menziesii) <5500

35 Ponderosa pine Favored abiotic conditions: Xeric sites All aspect in lower montane zone S-facing slopes in upper montane zone Shade-intolerant How can adults survive surface fires? Thick bark Self-pruning

36 What are two explanations for why a tree would be self-pruning?

37 Douglas fir Favored abiotic conditions: Mesic sites North-facing slopes in lower montane zone All aspects in upper montane zone Shade-tolerant

38 Forest Types in Boulder County Mid-Upper Montane Zone ( m) Mixed Conifer Ponderosa pine dominates on xeric slopes Douglas fir, lodgepole pine (Pinus contorta), aspen (Populus tremuloides) codominate <5500

39 Lodgepole pine Favored abiotic conditions: Shade-intolerant considered pioneer tree species in subalpine Grows well on nutrient poor, bare mineral soil Serotinous cones

40 Yellowstone Fires 1988 burned large stands of lodgepole pine (low frequency, high severity) Serotinous cones opened in fire and released seeds, initiating a new forest of lodgepole seedlings

41 Subalpine: Aspen Seedling establishment by root suckers Aspen recovery after fire Elk grazing reduces aspen establishment Subalpine fir growing in shade of aspen

42 Pando: world s largest organism?

43 Forest Types in Boulder County Subalpine Zone Lodgepole pine (Pinus contorta) Subalpine fir (Abies lasiocarpa) Engelmann spruce (Picea engelmannii) Aspen (Populus tremuloides) Limber pine (Pinus flexilis) <5500

44 Subalpine: Subalpine Fir and Engelmann Spruce Subalpine fir cones Engelmann spruce cones Subalpine fir Codominant Shade-tolerant

45 Subalpine: Limber Pine Symbiotic relationship with Clark s Nutcracker Grows in exposed, rocky outcrops Wingless seeds Depend on bird for dispersal

46 Pathogen: White Pine Blister Rust Non-native fungi which feeds off live tissue and weakens or girdles tree Limber pine infested with WPBR followed by MPB attack

47 Why is limber pine so susceptible to white pine blister rust?

48 Outline Fire type spectrum and effects 3 major Rocky Mountain forest types and associated tree species Historic Range of Variability and Federal Legislation Fire history across elevations and variable effects of fire suppression

49 Historic Range of Variability (HRV) Measure of historical variation of a condition, process, etc. before major anthropogenic change Tool for resource managers to evaluate current conditions/processes Baseline for restoration

50 Major fire years of 2000 and 2002 in the western U.S. triggered legislative and policy initiatives

51 Healthy Forests Restoration Act of 2003 Today, the forests and rangelands of the West have become unnaturally dense, and ecosystem health has suffered significantly. When coupled with seasonal droughts, these unhealthy forests, overloaded with fuels, are vulnerable to unnaturally severe wildfires.

52 Healthy Forests Restoration Act of 2003 Today, the forests and rangelands of the West have become unnaturally dense, and ecosystem health has suffered significantly. When coupled with seasonal droughts, these unhealthy forests, overloaded with fuels, are vulnerable to unnaturally severe wildfires. What are the goals? 1. Return ecological integrity (thin to return to HRV)

53 Healthy Forests Restoration Act of 2003 Today, the forests and rangelands of the West have become unnaturally dense, and ecosystem health has suffered significantly. When coupled with seasonal droughts, these unhealthy forests, overloaded with fuels, are vulnerable to unnaturally severe wildfires. What are the goals? 1. Restore historical forest conditions (decrease density) 2. Reduce risk of high severity fire (thin to remove overloaded fuels)

54 HFRA Premise Fire suppression ceased frequent, lowseverity fires 1. Unnaturally dense stands 2. Fuel loads outside HRV (creates ladder fuels) 3. Fire risk outside of HRV (high severity fires)

55 Southwestern Ponderosa Pine Forests fire suppression Photos by W.R. Mattoon, F.R. Herman and F. Biondi

56 fuels build up Circa 1930 Today Tree Tree establishment establishment Fire occurrence Fire suppression era Fire occurrence Fire occurrence Allen et al. 1998

57 HFRA Goals and Treatments HFRA goals: 1. Return ecosystem integrity (reduce density) 2. Reduce risk of high severity fire These goals can (theoretically) be simultaneously achieved for Southwestern ponderosa forests 1909 Can these goals be simultaneously achieved for Colorado s forests? 1994

58 Southwestern Ponderosa Pine Model Northern Colorado Front Range

59 Outline Fire type spectrum and effects 3 major Rocky Mountain forest types and associated tree species Historic Range of Variability and Federal Legislation Fire history across elevations and variable effects of fire suppression

60 Fire history of the Montane Zone <5500

61 Montane Zone 118 fire history sites (Veblen 2000, Sherriff 2004, Gartner et al. in press, Schoennagel et al. 2011) Data collected: Fire scars (reconstruct fire history) Age structure data (fire effects) Sherriff and Veblen 2006

62 Relative Frequency Establishment Date Relative Frequency Establishment Date Montane Zone Lower Montane Zone MFI < 30 yrs Fire suppression Establishment follows cessation of fires Upper Montane Zone MFI > 30 yrs Little establishment after 1920 Naturally dense stands Where should restoration efforts be focused?

63 Lower Montane Zone Upper Montane Zone Veblen and Lorenz 1991

64 Montane Zone Do the HFRA assumptions hold for the montane zone? 20% - lowest elevs likely outside of HRV (< 2200 m) Potentially outside HRV Thinning may restore forests May reduce fire risk Moderate to low severity fire may also restore forests 80% - mid-high elevs not outside HRV (> 2200m) Naturally dense due to naturally infrequent, variableseverity fires Thinning will not return ecological integrity May reduce fire risk

65 Montane Zone Do the HFRA assumptions hold for the montane zone? 20% - lowest elevs likely outside of HRV (< 2200 m) HRV frequent, low-severity fire Climate - drier Forest-grassland ecotone 80% - mid-high elevs not outside HRV (> 2200m) HRV infrequent, variable-severity fire Climate - wetter Lots of woody fuels, fewer grasses Sherriff and Veblen 2007

66 Montane Zone Palmer Drought Severity Index (PDSI) + values indicate wetter than avg climate - values indicate drier than avg climate Lower montane Fires burn during dry years with antecedent wet years Fuels are limiting Upper montane Fire burns during dry years Climate is limiting, not fuels Sherriff and Veblen 2008

67 Subalpine Zone <5500

68 Tree establishment Subalpine Zone High fuels loads were common before and now. Circa 1916 Today Tree establishment Fire suppression era Fire occurrence Veblen and Lorenz 1991 Sibold 2005

69 Subalpine Zone Infrequent, high-severity crown fires

70 Subalpine Zone Subalpine zone 1916 Little change in tree densities over the last century Fire suppression has had little effect Infrequent crown fires still are the dominant fire regime 1986 Is thinning a restoration treatment? Veblen and Lorenz 1991

71 Subalpine Zone Fire occurs during extreme drought in subalpine forests Climate-limited

72 Fact or Fiction? A century ago a ponderosa pine forest may have had some 25 mature trees per acre and be easily traversed on horseback or by a horse-drawn wagon. Today the same forest may have more than trees on the same acre, creating conditions that are much too thick for the passage of a hiker. These tightly packed trees are smaller, weaker, more disease prone and more susceptible to insect attack than their ancestors. Such forests form huge reservoirs of fuel awaiting ignition, and pose a particularly significant threat when drought is also a factor. USFS, 2011

73 Olde Stage Fire, 2009 Picnic Rock 2004 Olde Stage Fire, 2009 Picnic Rock 2004 Olde Stage Fire, 2009 George Kochaniec Dawes County fire, Nebraska Wildland Urban Interface (WUI) Rod Moraga

74 Housing density affects fire risk From: Western Futures

75 FIREWISE Probability of home ignition is independent of wildland fuels Cohen 2004

76 Home and its immediate surrounding within m affects home ignition (Cohen 2001) Home Ignition Zone Crown fire Surface fire

77 Home loss in WUI critical to fire risk discussion Fire risk in WUI is not necessarily due to fire suppression homes in WUI are at risk even under natural fire regimes Thinning may be desirable nearby homes, but restoration & fuel reduction are not often compatible

78 What are the consequences of thinning in areas not currently outside HRV? How well does thinning emulate fire?

79 Fire exclusion Fire exclusion & logging Burned, unlogged (reference) stands Unburned, unlogged stands Unburned, logged stands Burned, unlogged Unburned, unlogged Unburned, logged

80 Factors other than fire suppression important in current stand conditions Thinning may have long-term negative feedbacks, but this is not well understood Restoration need greater in previously logged stands than unlogged, fire suppressed stands

81