Effect of Catastrophic Fires

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    Potential soil changes in Mazama ash soils of the Upper

    Chewaucan watershed in the Fremont/Winema National

    Forest due to catastrophic wildfire in beetle killed, jackstrawed

    trees.

    Hayden Bush

    Clair Thomas M.S.

    CBMT

    February 2009

    Lake County Resource Initiative

    Chewaucan Biophysical Monitoring Crew

    25 North E. Street

    Lakeview, OR 97630

    www.lcri.org

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    Abstract:

    Mazama ash soils in the Upper Chewaucan Red Zone are sandy and coarse withmoderately thick litter and duff covering the soil. The combination of coarseness and litter,

    especially duff, cause organic hydrocarbons to be driven into the soil during intense burns

    under logs and where smoldering can occur. Mazama ash soils can be significantlychanged at temperatures of 200 C, apparently from the resins in pine needles which bond

    silts and sands together. Water repellent layers become a major soil feature at 400 C.

    Impact on Red Zone soils is controlled by the number of downed trees. Trees thatburn while standing direct their heat upward, it is only those trees next to the ground that

    endanger soil productivity. If 280 trees per acre fall within 5 to 10 years about 20% of the

    soil will contact or be directly under a jackstrawed tree. Recovery of soil generally takesplace over a few years, but seldom is 20% of the soil affected. What is the risk to the

    Upper Chewaucan Mazama ash soils?

    Background:Soils are fundamental to a healthy, functioning forest ecosystem. Soil properties

    may be compromised following severe wildfire. These changes include soil hydrology,biota, carbon, and nutrient cycling among others. The long term affects of these soil

    changes are only beginning to be understood.

    Most forests soils in standing timber appear to recover within a sort period of time,based on vegetative recovery. Most forest fires occur in standing timber which directs heat

    into the air rather than down-ward into the soil. Soil temperatures in these stands may

    only reach 100 C on the surface. Quick vegetative recovery may be deceptive as a means

    of determining soil health since temperatures of 50 60 C kills most soil biota. Fires instanding timber may be intense (long flame length) but not severe. Soil burn severity

    depends on the amount of heat energy released during a fire and the affect it has on the soiland water resources (Erickson, White, 2008). The coupled reaction of vaporization andcondensation provides a mechanism for the transfer of both water and organic materials

    through the soil during fires (DeBano, et al., 1998). Large quantities of downed wood

    where smoldering occurs can result in intense heat release and irreparable soil damage(40cm 50 cm deep) lasting many years (DeBano, Neary, Ffolliott, 2006). The Upper

    Chewacan Red Zone will have large quantities of downed wood within 4 years based on

    research conducted by the Chewaucan Biophysical Monitoring Team (attached tables andgraphs)

    If soil temperatures reach 175 200 C organic compounds vaporize and are driven

    by steep heat gradients down into the soil where they condense on cooler underlying soil

    particles. Thus, burning can create a semi-continuous or continuous water repellent layerat or beneath the soil surface , whose depth and thickness depend on the duration and

    magnitude of the soil heating (DeBano, 2000: Letey, 2001). At temperatures around 200 C

    consumption of all organic matter begins and at 400 C all organic matter is lost; so very hotfires produce a non-repellent, disaggregated soil layer above a water repellant layer

    (DeBano, 2000; Doerr et al., 2006).

    The scenario occurring during the destruction of soil structure by fire is:

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    The soil structure collapses and increases the density of the soil because the organic

    matter that served as a binding agent has been destroyed.

    The collapse in soil structure reduces soil porosity (mainly macropores)

    The soil surface is further compacted by raindrops when surface soil particles and

    ash are displaced, and surface soil pores become partially or totally sealed.

    Finally, the impenetrable soil surface reduces infiltration rates into the soil andproduces rapid runoff and hillslope erosion.

    (DeBano, Neary, 2005)

    Coarse-textured soils are more susceptible to the formation a water-repellent layer

    than fine-textured soils because of their lower surface area and greater air permeability

    (Huffman, et al., 2001; DeBano et al., 2005). Soils of the Upper Chewaucan watershed arecomposed of coarse grained Mazama ash.

    Upper Chewaucan watershed Forest and Soils:

    The forests of the Upper Chewaucan watershed are predominately lodgepole pine.Western Mountain Pine beetles (Dendronichus brevis) have devastated more than 700,000

    acreas of timber and are continuing to move across the Oregon Cascades. The beetles areattaching the largest and often healthiest trees in the stand leaving smaller and suppressed

    trees. In most stands the basal area is being reduced from around 300 to around 100, and

    the number of living trees is being reduced from 400 to 120, leaving around 280 standingsnags per acre. These snags become infected with fungus within the first year and many

    break off and are lying on the ground within 2 years. The Chewaucan Biophysical

    Monitoring Team estimates that 50% of all snags will be on the ground within 4 years, withthe larger beetle killed snags (>30cm) on the ground within 10 years.

    280 jackstrawed trees per acre pose a tremendous fire threat in the Red Zone for

    many years. The loss of an already established regenerating forest will be accompanied bysevere damage to forest soils. A study on the effect of burning logs and slash piles onjuniper soils (generally coarse textured) indicated that substantial changes occur in the

    mineralogy of the underlying soil (Iglesias, et al., 1997)

    The Chewaucan Biophysical monitoring team also found an average of 3cm of litterand duff currently covering the Red Zone soils (see appendices). Litter thickness will be

    much greater as tree fall apart. When thick layers of organic materials ignite, glowing

    combustion can create an ash layer on the surface of the glowing duff. This ash layerretards heat dissipation upward, thereby causing more heat to penetrate into the soil

    (Sackett and Haase, 1992) As a result organic layers can transfer 40 to 73 percent of the

    heat generated during the smoldering process into the underlying mineral soil (Hungerford,

    Ryan. 1996) This ignition, smoldering and combustion of thick duff layers can continue forhours, thereby allowing substantial time for heat to be transferred deeply into the soil

    (DeBano, Neary. 2005).

    Many reports describing soil temperatures during fire under a wide range ofvegetation types and fuel arrangements are present in the literature. I have included 2 from

    DeBano and Neary, 2005 under windrowed logs and under a larch forest with a 7cm duff

    layer.

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    CBMT Research and Discussion on Upper Chewaucan Red Zone Soils:

    The top 4 inches of soil from 8 survey areas in the Red Zone were collected and

    mixed. 34 samples were dried at 30 C overnight (24 hours). Dried samples were weighed,saturated with water and reweighed to calculate water holding capacity. 100 ml of water

    was poured through the sample and the percolation time was recorded. Samples were then

    redried for 24 hours.Samples were burned with an oxy/acetylene torch, adjusted for high oxygen and

    minimum acetylene held high above the ceramic flower pots filled with soil at a distance to

    ensure a constant temperature of 100 C. A Vernier thermocouple was inserted through thebottom of the clay pot1/4 of an inch below the soil surface. The samples were heated

    slowly and kept at temperature for 5 minutes. After cooling samples were reweighed, re

    saturated with water and tested for percolation. Samples were then redried , reheated and

    retested at 200 C. This process was repeated for 400 C and 800 C.Following percolation and water holding capacity tests at each temperature, the

    burned soil was poured into tubs containing 500ml of water. The tubs were agitated for 5

    minutes and then let stand to allow settling of soil particles. Turbidity tests were taken

    with a LaMotte 2020 turbidometer every 30 seconds.Bacterial samples were taken during four different trials at all 4 temperatures. Soils

    were allowed to cool before removing 1g samples. These were mixed in 10ml of watercreating a dilution. All were diluted the same, so all could be compared. 1ml aliquots of

    the vortexed samples were plated onto Petri film and incubated for 3 days and then

    counted. As each layer was sampled it was scraped off with a steel spatula and the nextlayer was sampled.

    Results:

    Mazama ash soils are predominately sand with a component of large pumice basedsand particles from 2 to 4 mm in size. It is covered with 1 to 3 cm of litter and duff,

    extending into the soil for 2 cm, much of it thatched. Mazama ash soils in the Upper

    Chewaucan watershed are often no more than 20 cm deep, overlying older cascade sandyloam soil. Figure 1 illustrates values of soil characteristics.

    Soil properties changed little as soils were heated from 20 C to 100 C. Organic

    material on the surface released vapor, some of which went through the soil and exited thehole in the bottom of the clay pot. Most of the litter and duff remained intact. Changes in

    the soils water holding capacity and percolation time were insignificant. Samples of soil

    on the surface and 1 cm below the surface were incubated for bacteria on nutrient Petri

    film. There were no colonies on the surface but at 1cm, bacteria were as numerous as thesamples incubated before initial burning. Bacteria testing results are in figure 4.

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    Soil Characteristics of Mazama Ash Soils in the Red Zone of the

    Upper Chewaucan Watershed, 2008

    44.89

    1.98

    8.506.21

    9.23

    0

    10

    20

    30

    40

    50

    Soil Depth Duff Depth Rhizome Depth Moisture (%) Soil Temp C

    depths

    (cm

    Figure 1: Mazama ash soil characteristics, from 48, tenth acre plots. Each plot wassampled in 10 locations for a total of 480 measurements of each parameter.

    As soils were heated from 100 C to 200 C, soil properties changed significantly.

    Results can be compared in figure 2. Water holding capacity decreased by 8%, however

    percolation time decreased by 600%. The texture of the soil became more coarse asorganic material, mainly from lodgepole pine needles, vaporized gluing silt and sand

    particles together. DeBano, (2000) and Doerr (2006) predicted that soils would becomemore fine and that movement of smaller particles into soil pore space might cause surface

    run-off rather than percolation. Their research was conducted on soils that were initially

    less coarse than Mazama ash soils and might account for the difference. Our soils werealso tested in vitro using a 320 grain sieve which stops silt but will let clay through. To

    reduce error we poured the filtrate back through the soil several times until the water in the

    bottom of the beaker was clear after running through the sieve. Only then did we testpercolation. It was noted that the sample did not wet nearly as readily as it had in the initial

    trials at 20 C indicating some hydrophobicity in the topmost layer of the soil. Petri film

    bacterial cultures showed little life on the surface, reduction of bacterial colonies at 0.5 cmand abundant life, comparable to the control at 1 cm.

    Figure 2 & 3: Testing results from 8 locations in the Upper Chewaucan watershed for

    Water Holding Capacity and Percolation Rates. Samples were mixed and 34 trials run ateach temperature.

    C o m p a r is o n o f W a te r H o l d in g C a p a c i ty o f M a

    B u r n e d f o r 5 m in u t e s a t V a r io u s T e m p e

    5 7 . 6 5 8 .05 1 . 3

    4 6 . 0

    0 . 0 0

    1 0 . 0 0

    2 0 . 0 0

    3 0 . 0 0

    4 0 . 0 0

    5 0 . 0 0

    6 0 . 0 0

    7 0 . 0 0

    20 C Te s ting 1 0 0 C Te s tin g 2 0 0 C Te s tin g 4 0 0 C Te s tin g

    ate

    od

    gcapacty(%)

    C o m p a r is o n o f P e r c o l a tio n R a te s in M a z a m a A

    f o r 5 m in u t e s a t In c r e a s in g T e m p e r a t u r

    0 . 7 0 .7

    3 .0

    3 . 6

    0 . 0 0

    0 . 5 0

    1 . 0 0

    1 . 5 0

    2 . 0 0

    2 . 5 0

    3 . 0 0

    3 . 5 0

    4 . 0 0

    2 0 C Tes tin g 1 0 0 C Te s tin g 2 0 0 C Tes tin g 4 00 C T

    percolationratio(g/s)

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    From 200 C to 400 C most of the organic material vaporized through the bottom of

    the clay pot, though 8 of our samples had recognizable wood pieces left. Soils were lefteven more coarse resulting in an additional 25% increase in percolation time. Soil mass

    decreased by an additional 25%, mostly due to the vaporization of most of the organic

    material. The water holding capacity again decreased by about 8%, but the biggest changewas in marble like structures that formed on the soil surface. In some trials a fine lattice

    network was left, but in most a small percent of glassy large bisked (plastic or glassy) soil

    particles were left. The soils became far less wet-able, requiring stirring and extended

    periods of time to pick up water.

    100 C 200 C 400 CFigure 4. These photographs show the settling rates of soils burned at the indicated

    temperatures. Samples were poured int 500ml of water, agitated for 5min, then allowed to

    sit for 1 minute before pictures were taken. The 20 C and 100 C samples never did clear up

    probably due to the amount of silt and clay present. The 200 C and 400 C samples bothcleared up quickly due to the welding of silt and clay particles to larger sand and aggregate

    particles by hydrocarbons forced through soil as organic debris burned. An interesting

    difference is the amount of low density soil surrounded by hydrocarbons that never did mixwith water or sink. Soils such as these would demonstrate high surface runoff and erosion

    following fire.

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    Comparison of Bacterial Counts at Various Depths in Mazama

    Ash Soils Following Burning for 5 minutes at Various

    Temperatures, 2008

    24000

    8 0 0

    24000 24000

    1800016000

    24000 24000 24000 24000

    0

    5000

    10000

    15000

    20000

    25000

    30000

    20 C 100 C 200 C 400 C

    meanbacterialcount

    Surface

    2.5cm

    5cm

    Figure 4: Bacteria on the surface, exposed to direct flame were always destroyed. Bacteria

    below the surface were only slightly affected apparently due to the insulating qualities ofsandy soils and the short period of time they were heated. Soils allowed to smolder over

    time destroy much more soil biota than intense short lived fires (Erickson and White,2008). Collert samples exceeding 24,000 bacteria were considered TNTC (too numerousto count) by TEP (Tillamook Estuaries Partnership) technitions. I gave them all values of

    24,000 on the graph. Petri film counts showed a reduction of bacteria cultures within the

    first cm of soil, but had normal counts at 2 cm. The exact percent of bacterial reductioncannot be calculated since the control amounts were TNTC.

    Soils heated to 800 C showed definite bisking over the surface of the soil changingit entirely. The plastic particles could be dissected to remove sand grains, indicating that

    sand was not being welded, beginning around 1400 C but still reacting to vaporized resins

    in the organic debris. A heat profile was made using 3 thermocouples during 3 of these

    trials. Temperature seems to decrease about 400 C/cm when soil is heated for 5 minutesonce it has reached target temperature. Figure 5 contains photographs showing bisking

    effects.

    20 C 100 C

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    200 C 400 C 800 C

    Figure 5: These photographs illustrate the differences in the soil following burning.

    Before burning at 20 C, organic material is un-scorched and soil particles are all sizes. At100 C, scorching of organic material is evident but soil particles are still present in all sizes.

    At 200 C, organic material is mostly gone, having been driven into the soil, evidenced by

    smoke coming out of the bottom of the pot. Small soil particles have been bisked into

    larger particles, though bisked particles are only recognizable as you look at them closely.At 400 C the surface of the soil is a spiderweb of bisked soil particles of all sizes. When

    teased, the surface tends to move as a single matrix over looser soil, however the matrixdoes break apart easily. At 800 C, the soil is totally altered soil particles being held

    together by hydrocarbon based plastic created from heated organic debris, especially pine

    needles.

    Discussion:

    Mazama ash soils in the Upper Chewaucan Red Zone are sandy and coarse with a3cm average of litter and duff. The combination of coarseness and litter, especially duff,

    cause organic hydrocarbons to be driven into the soil during intense burns under logs where

    smoldering occurs. The soil can be significantly changed at temperatures of 200 C, fromthe resins in pine needles which bind soil particles together. Water repellent layers become

    a major soil feature at 400 C.

    Impact of fire on Red Zone soils is controlled by the number of downed trees.Trees that burn while standing direct their heat upward, downed trees endanger soil

    characteristics through intense burn as well as long periods of smoldering. If 280 trees per

    acre fall within 5 to 10 years about 30% of the soil will contact or be directly under a

    jackstrawed tree. Recovery of soil following a catastrophic crown fire generally takesplace over a few years, but seldom is even 10% of the soil severely affected. In a

    jackstrawed burn, a fire of low intensity has much more severe effects on the soil and

    recovery could take decades. The ecology of the area could be drastically altered. Are thechanges in Mazama ash soils and resultant ecosystem changes of the Upper Chewacan

    Watershed worth risking?

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    Works Cited

    Erickson, White. 2008

    DeBano, et al., 1998

    DeBano, Neary, Folliott, 2006

    DeBano, 2000: Letey, 2001

    DeBano, 2000; Doerr et al., 2006

    DeBano, Neary, 2005

    Huffman, et al., 2001; DeBano et al., 2005

    Neary, Ryan, DeBano. 2005

    Sackett and Haase, 1992

    Hungerford, Ryan. 1996

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    Bibliography:

    Erickson, Heather and White, Rachel. Soils under fire: soils research and the Joint FireScience Program. Gen. Tech. Rep. PNW-GTR-759. Portland, Or. U.S. Department of

    Agriculture, Pacific Northwest Research Station, 2008

    Debano, L. F.; Neary, D.G.; Ffolliot, P.F. Fire's effects on ecosystems. New York: John Wiley

    and Sons, Inc. 333 p p. 1998.

    DeBano, The role of fire and soil heating on water repellency in wildland environments: a

    review. Journal of Hydrology: 231-232. May 29, 2000. pp. 198-206. 2000.

    Letey. Causes and consequences of fire-induced soil water repellency. WileyInterScience. Volume 15 Issue 15, Pages 2867 2875. October 25, 2001.

    Doerr et al. My current research focuses on three main areas. Swansea University:School of the Environment and Society. 2006.

    Huffman, Albright, et al., 2001 Post-Wildfire Erosion: Soil Hydrophobicity in ColoradoSoils. Soil Geography. December 13, 2007.

    Neary,D.G.; Ryan, K.C.; DeBano, L.F. Wildland fire in ecosystems: effects of fire on soils

    and water. Gen. Tech Rep. RMRS-GTR-42. Odgen, UT. U.S. Department of Agriculture,Rocky Mountain Research Station. 2005

    Sackett and Haase, 1992 Fire exclusion and nitrogen mineralization in low elevationforests of western Montana. Soil Biology and Biochemistry. Vol. 38, Issue 5. May 2006.

    pp. 952-961.

    Hungerford, R.D.; Harrington, M.G.; Frandsen, W.H.; Ryan, K.C.; Niehoff, G.J. 1991.

    Influence of Fire on Factors That Affect Site Productivity. In: Neuenschwander, L. F. andHarvey, A.E. comps.Management and Productivity of Western-Montane Forest Soils. Gen.

    Tech. Rpt. INT-280. Ogden, UT: U.S. Dept. of Agriculture, Forest Service, Intermountain

    Research Station: 32-50.

    http://www3.interscience.wiley.com/journal/86511044/issuehttp://www3.interscience.wiley.com/journal/86511044/issue