Effect of Catastrophic Fires

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<ul><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 1/10</p><p>Potential soil changes in Mazama ash soils of the Upper</p><p>Chewaucan watershed in the Fremont/Winema National</p><p>Forest due to catastrophic wildfire in beetle killed, jackstrawed</p><p>trees.</p><p>Hayden Bush</p><p>Clair Thomas M.S.</p><p>CBMT</p><p>February 2009</p><p>Lake County Resource Initiative</p><p>Chewaucan Biophysical Monitoring Crew</p><p>25 North E. Street</p><p>Lakeview, OR 97630</p><p>www.lcri.org</p></li><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 2/10</p><p>Abstract:</p><p>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,</p><p>especially duff, cause organic hydrocarbons to be driven into the soil during intense burns</p><p>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</p><p>silts and sands together. Water repellent layers become a major soil feature at 400 C.</p><p>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</p><p>endanger soil productivity. If 280 trees per acre fall within 5 to 10 years about 20% of the</p><p>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</p><p>Upper Chewaucan Mazama ash soils?</p><p>Background:Soils are fundamental to a healthy, functioning forest ecosystem. Soil properties</p><p>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</p><p>changes are only beginning to be understood.</p><p>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</p><p>into the air rather than down-ward into the soil. Soil temperatures in these stands may</p><p>only reach 100 C on the surface. Quick vegetative recovery may be deceptive as a means</p><p>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</p><p>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</p><p>through the soil during fires (DeBano, et al., 1998). Large quantities of downed wood</p><p>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</p><p>Chewacan Red Zone will have large quantities of downed wood within 4 years based on</p><p>research conducted by the Chewaucan Biophysical Monitoring Team (attached tables andgraphs)</p><p>If soil temperatures reach 175 200 C organic compounds vaporize and are driven</p><p>by steep heat gradients down into the soil where they condense on cooler underlying soil</p><p>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</p><p>magnitude of the soil heating (DeBano, 2000: Letey, 2001). At temperatures around 200 C</p><p>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</p><p>(DeBano, 2000; Doerr et al., 2006).</p><p>The scenario occurring during the destruction of soil structure by fire is:</p></li><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 3/10</p><p> The soil structure collapses and increases the density of the soil because the organic</p><p>matter that served as a binding agent has been destroyed.</p><p> The collapse in soil structure reduces soil porosity (mainly macropores)</p><p> The soil surface is further compacted by raindrops when surface soil particles and</p><p>ash are displaced, and surface soil pores become partially or totally sealed.</p><p> Finally, the impenetrable soil surface reduces infiltration rates into the soil andproduces rapid runoff and hillslope erosion.</p><p>(DeBano, Neary, 2005)</p><p>Coarse-textured soils are more susceptible to the formation a water-repellent layer</p><p>than fine-textured soils because of their lower surface area and greater air permeability</p><p>(Huffman, et al., 2001; DeBano et al., 2005). Soils of the Upper Chewaucan watershed arecomposed of coarse grained Mazama ash.</p><p>Upper Chewaucan watershed Forest and Soils:</p><p>The forests of the Upper Chewaucan watershed are predominately lodgepole pine.Western Mountain Pine beetles (Dendronichus brevis) have devastated more than 700,000</p><p>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</p><p>trees. In most stands the basal area is being reduced from around 300 to around 100, and</p><p>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</p><p>break off and are lying on the ground within 2 years. The Chewaucan Biophysical</p><p>Monitoring Team estimates that 50% of all snags will be on the ground within 4 years, withthe larger beetle killed snags (&gt;30cm) on the ground within 10 years.</p><p>280 jackstrawed trees per acre pose a tremendous fire threat in the Red Zone for</p><p>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</p><p>mineralogy of the underlying soil (Iglesias, et al., 1997)</p><p>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</p><p>much greater as tree fall apart. When thick layers of organic materials ignite, glowing</p><p>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</p><p>(Sackett and Haase, 1992) As a result organic layers can transfer 40 to 73 percent of the</p><p>heat generated during the smoldering process into the underlying mineral soil (Hungerford,</p><p>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</p><p>(DeBano, Neary. 2005).</p><p>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</p><p>DeBano and Neary, 2005 under windrowed logs and under a larch forest with a 7cm duff</p><p>layer.</p></li><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 4/10</p><p>CBMT Research and Discussion on Upper Chewaucan Red Zone Soils:</p><p>The top 4 inches of soil from 8 survey areas in the Red Zone were collected and</p><p>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</p><p>was poured through the sample and the percolation time was recorded. Samples were then</p><p>redried for 24 hours.Samples were burned with an oxy/acetylene torch, adjusted for high oxygen and</p><p>minimum acetylene held high above the ceramic flower pots filled with soil at a distance to</p><p>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</p><p>slowly and kept at temperature for 5 minutes. After cooling samples were reweighed, re</p><p>saturated with water and tested for percolation. Samples were then redried , reheated and</p><p>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</p><p>burned soil was poured into tubs containing 500ml of water. The tubs were agitated for 5</p><p>minutes and then let stand to allow settling of soil particles. Turbidity tests were taken</p><p>with a LaMotte 2020 turbidometer every 30 seconds.Bacterial samples were taken during four different trials at all 4 temperatures. Soils</p><p>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</p><p>the vortexed samples were plated onto Petri film and incubated for 3 days and then</p><p>counted. As each layer was sampled it was scraped off with a steel spatula and the nextlayer was sampled.</p><p>Results:</p><p>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,</p><p>extending into the soil for 2 cm, much of it thatched. Mazama ash soils in the Upper</p><p>Chewaucan watershed are often no more than 20 cm deep, overlying older cascade sandyloam soil. Figure 1 illustrates values of soil characteristics.</p><p>Soil properties changed little as soils were heated from 20 C to 100 C. Organic</p><p>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</p><p>the soils water holding capacity and percolation time were insignificant. Samples of soil</p><p>on the surface and 1 cm below the surface were incubated for bacteria on nutrient Petri</p><p>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.</p></li><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 5/10</p><p>Soil Characteristics of Mazama Ash Soils in the Red Zone of the</p><p>Upper Chewaucan Watershed, 2008</p><p>44.89</p><p>1.98</p><p>8.506.21</p><p>9.23</p><p>0</p><p>10</p><p>20</p><p>30</p><p>40</p><p>50</p><p>Soil Depth Duff Depth Rhizome Depth Moisture (%) Soil Temp C</p><p>depths</p><p>(cm</p><p>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.</p><p>As soils were heated from 100 C to 200 C, soil properties changed significantly.</p><p>Results can be compared in figure 2. Water holding capacity decreased by 8%, however</p><p>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</p><p>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</p><p>run-off rather than percolation. Their research was conducted on soils that were initially</p><p>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</p><p>reduce error we poured the filtrate back through the soil several times until the water in the</p><p>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</p><p>trials at 20 C indicating some hydrophobicity in the topmost layer of the soil. Petri film</p><p>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.</p><p>Figure 2 &amp; 3: Testing results from 8 locations in the Upper Chewaucan watershed for</p><p>Water Holding Capacity and Percolation Rates. Samples were mixed and 34 trials run ateach temperature.</p><p>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</p><p>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</p><p>5 7 . 6 5 8 .05 1 . 3</p><p>4 6 . 0</p><p>0 . 0 0</p><p>1 0 . 0 0</p><p>2 0 . 0 0</p><p>3 0 . 0 0</p><p>4 0 . 0 0</p><p>5 0 . 0 0</p><p>6 0 . 0 0</p><p>7 0 . 0 0</p><p>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</p><p>ate</p><p>od</p><p>gcapacty(%)</p><p>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</p><p>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 </p><p>0 . 7 0 .7</p><p>3 .0</p><p>3 . 6</p><p>0 . 0 0</p><p>0 . 5 0</p><p>1 . 0 0</p><p>1 . 5 0</p><p>2 . 0 0</p><p>2 . 5 0</p><p>3 . 0 0</p><p>3 . 5 0</p><p>4 . 0 0</p><p>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</p><p>percolationratio(g/s)</p></li><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 6/10</p><p>From 200 C to 400 C most of the organic material vaporized through the bottom of</p><p>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</p><p>decreased by an additional 25%, mostly due to the vaporization of most of the organic</p><p>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</p><p>network was left, but in most a small percent of glassy large bisked (plastic or glassy) soil</p><p>particles were left. The soils became far less wet-able, requiring stirring and extended</p><p>periods of time to pick up water.</p><p>100 C 200 C 400 CFigure 4. These photographs show the settling rates of soils burned at the indicated</p><p>temperatures. Samples were poured int 500ml of water, agitated for 5min, then allowed to</p><p>sit for 1 minute before pictures were taken. The 20 C and 100 C samples never did clear up</p><p>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</p><p>particles by hydrocarbons forced through soil as organic debris burned. An interesting</p><p>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</p><p>following fire.</p></li><li><p>7/31/2019 Effect of Catastrophic Fires</p><p> 7/10</p><p>Comparison of Bacterial Counts at Various Depths in Mazama</p><p>Ash Soils Following Burning for 5 minutes at Various</p><p>Temperatures, 2008</p><p>24000</p><p>8 0 0</p><p>24000 24000</p><p>1800016000</p><p>24000 24000 24000 24000</p><p>0</p><p>5000</p><p>10000</p><p>15000</p><p>20000</p><p>25000</p><p>30000</p><p>20 C 100 C 200 C 400 C</p><p>meanbacterialcount</p><p>Surface</p><p>2.5cm</p><p>5cm</p><p>Figure 4: Bacteria on the surface, exposed to direct flame were always destroyed. Bacteria</p><p>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</p><p>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</p><p>24,000 on the graph. Petri film counts showed a reduction of bacteria cultures within the</p><p>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.</p><p>Soil...</p></li></ul>