Effects of Catastrophic Fires and Salvage Logging on Forest Soils in the Fremont

7/31/2019 Effects of Catastrophic Fires and Salvage Logging on Forest Soils in the Fremont

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The Biogeochemical Effects of Catastrophic Fires and Salvage Loggingon Forest Soils in the Fremont-Winema National Forest

Jacinda ThomasClair Thomas, MS

March 2008

Lake County Resources InitiativeChewaucan Biophysical Monitoring Team

25 North E StreetLakeview, OR 97630


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lcri.org

Background

On July 23, 2002, lightning struck in southern Oregon, sparking a fire that

consumed approximately 42,000 forest acres. After 10 days, the fire crews wereable to get it under control but only after losing an estimated total of 88,000acres.

Importance

Soil nutrient changes brought on by fire can have immense repercussions onfuture forest development. Vegetation depends on soil nutrients to survive:perennials in the late seral stage of succession, such as mature forests, depend onammonium-nitrogen; nitrite is an intermediate step between the change fromammonia to nitrate and can be highly toxic; annuals, such as pioneering species,rely on nitrate-nitrogen; phosphates make up the phospholipid bilayer in cellmembranes as well as the energy molecule Adenosine Tri Phosphate (ATP); andpotassium aids in root osmosis.

Nitrogen

Nitrogen is an inert gas and makes up approximately 78% of the Earthsatmosphere. It can be fixed by lightning but mostly by bacteria living in soil. Thebacteria fix the nitrogen for their own use and it is not until their death thatthey release it (Ingham). Because the bacteria have died, the fixed nitrogen is nowammonium-nitrogen. Perennials prefer to utilize ammonia, as can annuals.When the plant dies, it will return to the soil. Ammonia not taken-up can become

nitrite-nitrogen, an intermediate step between ammonium-nitrogen and nitrate-nitrogen. Once it becomes nitrate-nitrogen, annuals prefer to take it up andsometimes perennials make use of it. Throughout the cycle, nitrogen candenitrify and change back to inert nitrogen gas. Phosphate and potassium comefrom volcanic rock; potassium usually in the form of potash. What happens to these nutrients after a catastrophic fire sweeps through,leaving no vegetation? Any heating of the organic layer and the upper six inchesof the mineral soil can have serious repercussions on post-fire forest productivitybecause the bulk of nutrients and the activity of soil organisms are concentratedthere. Low severity fires heat the soil surface to 400 degrees Fahrenheit or less,leave blackened soil surfaces and minimally impact the soil except on its surface.

Fires that reach 550 degrees Fahrenheit or less are considered moderately severe.These fires generally consume all organic material on the soil surface but at atemperature that mineralizes soil macro-nutrients making them available forplant up-take. Moderately severe fires tend to have higher nitrogenconcentrations immediately following the fire, but tend to lose most of thenitrogen over the course of the first year. High severity fires cause soils to reachtemperatures in excess of 572 degrees Fahrenheit where nitrogen compoundsvolatilize to nitrogen gas. These soils are nitrogen poor following the fire.

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Soil studies detailing soil nutrients trends after the first year are difficult tofind. Six years after the fire, raw data was taken from burned areas to be analyzedfor this study.

Methods/Materials

Surveyed sites were randomly chosen using GIS layers (ESRI) based on similarcharacteristics. The 45 sites chosen were west-facing with a 6-15 slope, sandyloam soils lacking abundant boulders and populated with Ponderosa pine andWhite fir. 70% non-burned, 30% burned, and burned and harvested wererandomly selected. The randomly selected sites were visited for closer inspection.The sites were examined for similar pre-burned tree characteristics: densities of150-200 trees per acre; diameters at breast height averaged 25-40cm; 20 trees orless greater than 45cm; and with 20-30 small trees less than 20cm.

Once the sites were found to be comparable, the center of a stand was foundusing a compass and a 30m tape, and a random number between 0 and 360 wasused for direction to transect. A random number was again selected for thedistance in paces to point A of plot. After locating point A, a random number wasselected for the direction of the transect line and then the tape was stretched out.Soil data was taken at every 3m mark. Soil temperature was measured with theWeksler soil thermometer; Field Scout Soil Compaction M-900 was used forcompaction, AMS Tile Probe for soil depth, Field Scout Soil Moisture Meter 700for moisture, a caliper to measure rhizome depth, and the Soil Sampling Augur totake soil samples.

Soil samples representative of the site were taken at the A and B stake andbagged for soil testing. Using the LaMotte Smart 2 SoilSpectrophotometer/Colorimeter and protocols developed by LaMotte for soilAmmonia, Nitrite, Nitrate, Phosphate, and Potassium. The samples were

analyzed and recorded in parts per million (mg/L). Graphs are in the appendix.

Results of soil characteristics:

Comparisons between burned areas and unburned areas revealed significantchanges:

1. soil depth decreased by 29%,2. duff depth increased by 94%,3. rhizome depth increased by 13%,4. percent moisture decreased by 500%, and5. soil temperature increased by 12%.

Compaction decreased by 38.6% but this proved insignificant

Comparisons between burned areas and burned areas that weresalvaged revealed insignificant changes despite:

1. soil depth increased by 11%,2. duff depth was similar and mostly absent,3. rhizome depth increased by 3%,4. percent moisture decreased by 25%, and

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5. compaction decreased by 14%Temperature increased significantly by 9%.

The following explanations are given concerning changes between the nonburned control and burned areas and between the burned areas compared to the

burned and salvaged areas:1. Soil depth decreased due to high temperatures resulting in friable soilpeds losing structural integrity and settling over time, Soil depthincreasing slightly after logging is confusing though sub-soiling may havebeen performed in enough areas to statistically show deeper soils

2. Duff depth decreased because the moderately severe fire removed thelitter layer leaving a thin layer of ash,

3. Rhizome depth increased as a possible result of the small ash particlesfrom the fire leaching throughout the soil horizons and settling in lowerlayers causing the rhizomes to move deeper for nutrients,

4. Percent moisture decreased because shade was removed exposing the soilto sunlight drying it out. During salvage the establishing plants weredisturbed, again allowing in more sunlight to heat the soil and dry itfarther,

5. Compaction decreased as a result of heating water in the soil, expandingwater pockets. However the soil becomes very fragile when this happensand is easily compacted when disturbed. The lower compaction valuescould also result from sub-soiling practices that occurred in some of theareas, and

6. Temperatures increased because soil was exposed due to loss of vegetativecover. This may appear negative but does have some positiveimplications; higher temperature less than 90 causes microbes in thesoil to increase their activity; cycling soil nutrients.

Results of soil chemistry:

Comparisons of unburned with burned areas revealed that nitrogen macro-nutrients decreased while phosphorus and potassium macro-nutrients increased:

1. Ammonia decreased by 36%; nitrite decreased by 63% and nitratedecreased by 53%. Ammonia and nitrate decreasing in the soil couldindicate one of two things: the area is recovering and vegetation is utilizingthe nutrients; or because there are no vegetation or soil microbes to utilizethem, the nutrients have denitrified into inert nitrogen.

2. Phosphate increased by 397% probably due to the lack of plants that utilizeit and its ability to be stored in the soil for long periods of time.

3. Potassium is similar at +4% which falls within the relative error of themean and deviation.

Comparisons of burned areas with burned salvaged areas revealed:1. Ammonia decreased by another 15%; nitrite increased by 50%; nitrates

increased by 27%. Ammonia decrease in the soil could indicate one of two

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Appendix

Soil Characteristics Graphs

Comparison of Depth in Forest Soils

5 3 . 4

2 .5

3 7 .8

0.1

4 2 . 4

6 6 .9

0

7 .1

0

1 0

20

30

40

50

60

7 0

Soil Duff Rhizome

depth(cm)

Unburned

Burned

Bur ned Salv age

Comparison of Moisture in Forest Soils

4.8

18

3.6

0

5

10

15

20

25

percentmoisture Unburned

Burned

Burn ed Salv age

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Comparison of Temperature in Forest

Soils

17 . 6 19.9

21.9

0

5

1 0

1 5

20

25

30

degreescentigra

de

Unburned

Burned

Burned Salv ag e

Comparison of Compaction in Forest

Soils

135.8

115.1

99.4

0

20

40

60

80

1 00

1 20

1 40

1 60

1 80

pou

ndspersquareinch(psi)

Unburned

Burned

Bur ned Salv ag e

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Soil Chemistry Graphs

Comparison of Nitrogen Levels in Forest

Soils

0.7 4

0.47

0.34

0.08

0.03

0 . 1 60.22

0.06

0.4

0

0.1

0.2

0.3

0.4

0.5

0.6

0. 7

0.8

0.91

NH4- NO2-N NO3-N

concentration(ppm)

Unburned

Burned

Bur ned Salv ag e

Comparison of Potassium and Phosphate

in Forest Soils

1 . 6 3

7 .17 1

6 . 4 5

5 . 1 3

7 .1 77 .47

0

1

2

34

5

6

7

8

9

10

PO4 K

concentration(ppm)

Unburned

Burned

Bur ned Salv age

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Works Cited

Bitterroot National Forest. 2000. Bitterroot Fires 2000: An assessment of post-fire conditions with recovery recommendations. USDA Forest Service,Bitterroot National Forest. Unpublished report available online at

http://www.fs.fed.us/r1/bitterroot/recovery/fires_2000-screen.pdf.

Cilimburg, A. C., and K. C. Short. 2005. Forest fire in the U. S. Northern Rockies:a primer. RetrievedMarch 3, 2008 from http://www.northernrockiesfire.org.

Giesen, Thomas William. 2006. Four centuries of soil carbon and nitrogenchange after severe fire in a Western Cascade forest landscape.

Ingham, Dr. Elaine. The Nitrogen Cycle and the Soil Food Web. 2005. Onlineessay available at

Macadam, A. 1989. Effects of prescribed fire on forest soils. B.C. Min. For.,Victoria, B.C. Research Rep. 89001-PR.

Raison, R.J. 1979. Modification of the soil environment by vegetation fires, withparticular reference to nitrogen transformations: a review. Plant and Soil51: 73-108.

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http://www.fs.fed.us/r1/bitterroot/recovery/fires_2000-screen.pdfhttp://www.fs.fed.us/r1/bitterroot/recovery/fires_2000-screen.pdfhttp://www.fs.fed.us/r1/bitterroot/recovery/fires_2000-screen.pdfhttp://www.fs.fed.us/r1/bitterroot/recovery/fires_2000-screen.pdf

Effects of Catastrophic Fires and Salvage Logging on Forest Soils in the Fremont

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