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Methods for Experiment 012 -

Burning LTER Plots

All of the burning done within LTER experiments at Cedar Creek Natural History Area are done in late April or early May. Burn permits are issued to Cedar Creek Natural History Area for this time, and the following areas within Cedar Creek, by the Department of Natural Resources (headquarters in Cambridge, MN). In all cases, several people are on hand to help contain the fire. Tools used are "flappers", shovels and hand-pumped, portable water spray-cans. Drip torches containing a mixture of 1/3 gasoline and 2/3 diesel are used to start the fires. A truck carrying a high pressure water sprayer hooked up to a 125 gallon tank of water is always nearby. After the fires are burned out, any remaining hotspots are extinguished or moved to the center of the burned area to insure the prevention of wildfires.

125 gallon water tank and Minnesota Warmer Co. model KW125-7-10 utility sprayer.

Field Operations: Burn Problems

1990: Plot 11 had a small escaped fire in the southwest corner.
1995: On May 5th a wildfire burned all of the plots in experiment 12 in field B.

Field Operations: Burning

There are four different burn treatments:

1. plots burned every year
2. plots burned every other year
3. control = plots are not burned
4. plots burned every fourth year.

Burning is done in the spring. In preparation for burning, the perimeter of groups of plots to be burned is mowed using a lawn mower. The cuttings and litter remaining are then raked into the area to be burned. This firebreak is then reinforced by wetting the cropped vegetation with a high pressure water hose attached to a 125 gallon water tank. A backfire is started to widen the fire- break. A drip torch is then used to start the groups of plots (one at a time) on fire.

Field Operations: Burning Schedule

YearTreatments burned
1983None
19841, 2, 4
19851
19861, 2
19871
19881, 2, 4
19891
19901, 2
19911
19921, 2, 4
19931
19941, 2
1995all (wildfire)
19961
19971, 2
19981
19991, 2, 4
20001
20011, 2
20021
20031, 2, 4
20041
20051, 2
20061, 2, 4
20071
20081
20091, 2
20101
20111, 2, 4
20121
20131 , 2
20141
 

Treatment layout for E012

Field Identification Experiment Number Plot Number Fire Treatment
B1214
B1221
B1234
B1243
B1251
B1261
B1273
B1284
B1292
B12102
B12114
B12122
B12134
B12143
B12151
B12162
B12173
B12183
B12192
B12201
B12214
B12223
B12232
B12241
 

adve012 - Root biomass

Root biomass

At the peak of standing biomass, vegetation was sampled by clipping a 10-cm by 3-m long strip at ground level within each plot. Roots were collected from the strip clipped for vegetation sampling using three 5-cm-diameter cores from each plot: 0 to 20, 20 to 40, 40 to 60, and 60 to 100 cm. Roots were washed and handpicked over a 1-mm screen to remove all soil, pebbles, and debris and then dried at 60??C and weighed.

adwe012 - Root carbon and nitrogen

Root Carbon and Nitrogen

Roots were collected using three 5-cm-diameter cores from each plot: 0 to 20, 20 to 40, 40 to 60, and 60 to 100 cm. Roots were washed and handpicked over a 1-mm screen to remove all soil, pebbles, and debris and then dried and weighed. Roots were ground prior to analysis.

Root carbon and nitrogen

Roots were ground using a Wiley mill (Thomas Scientific, Swedesboro, NJ).

Samples were analyzed on a Costech ECS 4010 (Costech Analytical Technologies, Valencia, CA) for % C and N.

adxe012 - Plant aboveground biomass carbon and nitrogen

Plant aboveground biomass carbon and nitrogen

At the peak of standing biomass, vegetation was sampled by clipping a 10-cm by 3-m long strip at ground level within each plot in mid-July of 2000, and 2010. All clipped samples were sorted to individual plant species and litter. Samples were dried at 60?C and ground for analysis of carbon and nitrogen.

Plant aboveground biomass carbon and nitrogen

Plant aboveground biomass samples were ground using a Wiley mill (Thomas Scientific, Swedesboro, NJ).

Samples were analyzed on a Costech ECS 4010 (Costech Analytical Technologies, Valencia, CA) for % C and N.

adye012 - Soil bulk density

Soil bulk density

A 5-cm- diameter corer was used to collect one soil sample at the same depths within each plot. These samples were dried and weighed to determine bulk density.

adze012 - Soil carbon and nitrogen

Soil carbon and nitrogen

Soil samples were collected in mid- July of 2000 and 2010. Soil samples of the depth intervals 0 to 10, 10 to 20, 20 to 40, 40 to 60, 60 to 80, and 80 to 100 cm from each plot were taken by a 5-cm-diameter soil core. The soils were dried and sifted through a 2-mm sieve to remove roots. The sieved samples were ground in a coffee mill, dried to 60?C and analyzed for carbon and nitrogen.

Soil carbon and nitrogen

Samples were analyzed on a Costech ECS 4010 (Costech Analytical Technologies, Valencia, CA) for % C and N.

aeae012 - Soil Nitrogen Cycling

Soil Nitrogen Cycling

We measured gross ammonification and gross nitrification rates using 15N isotopic- pool dilution (Hart et al., 1994) in the surface soil, 0 to 10 cm deep. To determine gross ammonification rates, an approximate 250 g (fresh weight) homogenized and sieved soil sample was injected with 10 mL of 0.147 mmol L-1 solution of (15NH4)2SO4 (99% atom). To determine gross nitrification rates, an approximate 250 g (f.w) homogenized and sieved soil sample was injected with 10 mL of 0.301 mmol L-1 solution of K15NO3 (99% atom). Each sample was mixed in a resealable plastic bag to ensure homogenous distribution of 15N solution. After 15N addition one soil sample [an approximate 50 g of soil (f.w.)] of each labeled pair was extracted immediately with 75 mL of 2 mol L-1 KCl [time 0 samples (T0)] to determine initial NH4 and NO3 pool size, respectively. Another remaining labeled soil was resealed in the bag to stop the loss of any moisture from the sample and was incubated in the dark at roomtemperature (22?C) for 24 h. After the 24-h incubation period, time 1 samples (T1) were extracted in the same way that the initial samples were extracted. To determine 15N enrichment levels at both T0 and T1, N from soil extracts was concentrated by diffusion onto paper discs following Hart et al. (1994)and subsequently analyzed for 15N/14N by a stable isotope mass spectrometer at the University of California, Davis, Stable Isotope Facility (Europa Integra). Gross N cycling rates were calculated using T0 and T1 following Eq. [1] (Takahashi, 2001): where mN is the gross ammonification or nitrification rate (mg N kg-1 soil d-1); Pool1 NH4 or NO3 concentration at T1 and Pool0 NH4 or NO3 concentration at T0; APE1 is the atom percent 15N excess of NH4 or NO3 pool at T1 and APE0 is the atom percent 15N excess of NH4 or NO3 pool at T0 (Hart et al., 1994).

Published results and illustrated methods from this data in: Li, Wenjin; Knops, Johannes (Jean) M.H.; Zuo, Xiaoan; Laungani, Ramesh; Carbon and Nitrogen Cycling are Resistant to Fire in Nutrient-Poor Grassland; Soil Sci.Soc.Am.J., 78, 3, 825 - 831 2014

Method references cited:
Hart, S.C., J.M. Stark, E.A. Davidson, and M.K. Firestone. 1994. Nitrogen mineralization, immobilization, and nitrification. In: R. Weaver, J. Angle, and P. Bottomley, editors, Methods of soil analysis. Part 2.. SSSA, Madison, WI. p. 985?1018.

Takahashi, S. 2001. Comparison of gross nitrogen mineralization rates by Zero-OrderModels. Soil Sci. Soc. Am. J. 65:244?246. doi:10.2136/sssaj2001.651244x

lpe012 - Percent light penetration

Light Penetration

Light meter readings for E012 were taken in 1987 and 1990. Readings were taken .5m from the front and back of each plot. The distance from the left or right edge varied from year to year. If light readings were taken before the vegetation was sampled that year, the light readings were taken in the location of the clip strip. If light readings were taken after the vegetation had been clipped, the location of the light readings was moved to one side, or the other, of the clip strip so the bare spot would not affect the readings. Usually, a set of readings was taken from the front of the plot and a second set was taken from the back of the plot. The date, time, field, plot, side (left or right), front or back, distance from the side of the plot, range value (before 1988) and the display reading were all recorded for each measurement. Light meter readings were taken in the same positions in all plots, regardless of the presence of gopher mounds.

Light Penetration Measurements

From 1982 to 1988, light meter readings were taken using a Li-Cor, Inc. Integrating Quantum/Radiometer/Photometer, model LI-188B. Two people were needed to take light readings with this system. One would hold the control box and record data and the other would hold the light sensor. The batteries would be checked before starting each session. If the batteries were OK, they would proceed to take readings. The sensor was connected to the control box by a relatively short cord, so the two people taking readings were required to stay close together. When taking readings, it was necessary to get a range value for each light value entered. If the integrating time of 1 second was not sufficient, it was increased to 10 seconds. This was also recorded.

In 1989, two new light meters were acquired. These are SF Sunfleck Ceptometers, model SF-40 (40cm probe). They were purchased from Decagon Devices, Inc., P.O. Box 835, Pullman, WA 99163. One person can easily handle a ceptometer alone. This makes is possible for three people to get the readings done more quickly and easily. One person records data while the other two take readings from the plots simultaneously. No range values are needed. To take readings a person needs to select function #1 (PAR readings), position the probe (see below) and press ``A' (read value). More than one reading can be taken and then averaged by pressing a certain sequence of letters (A, A, B, B, A).

Measurements are taken within a 4 hour period, 2 hours on either side of solar noon. (Solar noon is half way between sunrise and sunset; it is not 1200 hours). Solar noon is at 1315 hours, Central Daylight Time. Samples are taken between 1115 hours and 1515 hours. Measurements are not taken when the plot being sampled is shaded. Light readings are done when the sky is clear, whenever possible. If a cloud passes over the plot being sampled, assistants wait for the cloud to pass before taking the readings. If the sky is mostly cloudy, light meter readings are not taken.

Two measurements are taken in each plot. Each measurement consists of one reading above the vegetation and a second reading at ground level. Both values are taken to get the percent of sunlight above the vegetation that reaches ground level. In taking the above vegetation reading, the sensor must be kept level, held high above all vegetation, kept out of the shade (of plants and people) and it must be clean. When taking the below vegetation reading, at ground level, the sensor must be kept level, out of the soil and out of the shade created by people.

In 1991, light meter readings were only taken in E026 and E055. Light profiles were taken using an A-shaped frame made of aluminum. Wires were strung across the frame at 10cm intervals. The frame was placed over the subplot being metered. A reading was taken over the top of the frame, and then at each 10cm level, by placing the light meter across the wires, starting at 90cm above the ground. Readings were taken every 10cm down the frame and again at ground level.
Light Data Transformations:
Light readings are transformed to obtain percent light penetration which represents the percent of light above the vegetation that reaches the ground surface. In cases where the experiment involves shading, another variable is computed to reflect the percent of sun light that reaches above the canopy. This variable is called light available. In the case of absence of artificial shades, the latter is set to 1.

percent light penetration = ( Light below canopy / Light above canopy ).

percent light available = ( Light below shade / Light above shade ).

ple012 - Plant aboveground biomass data

Listing of location of aboveground vegetation sampling in E012

Year Clipped Area
1983 Clipped 2 to 2.1m from left, 0.5 to 3.5m from bottom
1983 Clipped 5.9 to 6m from left, 4.5 to 7.5m from bottom
1987 Clipped 4 to 4.1m from left, 1 to 4m from bottom
1991 Clipped 3 to 3.1m from left, 1 to 4m from bottom
2002 Clipped 2.5 to 2.6m from left, 4 to 7m from bottom
2002 Clipped 5.4 to 5.5m from left, 1 to 4m from bottom

Sampling Discrepancies in E012
Year Sampling Discrepancy
1983 none
1987 none
1991 none
2000 none

Vegetation Sampling

Plots in this experiment are sampled every four years. Each time it is sampled, the sample strip is located in a different place. A 10cm x 3m strip of vegetation is clipped out of each plot. Documentation on where the strips are located for each year can be found in the clipping maps.