leaf litter

Plant Litter Decomposition at the Sevilleta National Wildlife Refuge, New Mexico (1990-1998)

Abstract: 

The long-term goal of the decomposition study was to document the effects of climate variation on decomposition of major plant litter-types. The project began in 1989 and underwent changes of locations and litter types. The long-term litter types included black grama, Indian rice grass, juniper, and creosote.  Mass loss of the litter types can be compared to precipitation and other meteorological factors obtained at nearby locations.

Data set ID: 

12

Core Areas: 

Additional Project roles: 

289

Keywords: 

Data sources: 

sev012_ltdecomp_20130326.txt

Methods: 

Experimental Design:  

Setting up each location: 1989 through 1991:

The design of this decomposition study includes placement of three (3) primary litter-types (black grama, juniper, and indian rice grass) at seven (7) locations. Litter of each species was collected after senescence in the fall. The grasses were clipped from standing plants before the litter was on the ground. All material that was not produced during the previous growing season was discarded.  All reproductive parts were discarded. If there was any doubt about whether or not the material was produced that growing season, it was discarded. Juniper was collected from trees with senescent material or that had recently died and were still on the branch. Juniper litter consisted of only that material that still had bracts (woody stems without bracts were discarded). Pinyon was collected from trees that still retained senescent needles by shaking and capturing on a cloth or plastic sheet.  Branches of 4-wing saltbush were trimmed from bushes in October when material looked senescent and leaves were picked from the branches and air-dried. Creosote leaves were attempted to be collected by spreading sheets on the ground; however, litterfall is very episodic and not enough material could be collected. Thus, creosote was collected by cutting live plants and drying in a forced-air oven at 60 °C; then the freshly dried leaves were removed from the branch and any reproductive parts (seeds) were discarded. Yucca was collected by cutting leaves from a recently dead yucca plant. Cottonwood leaves were collected in plastic trays as they fell and before the fresh litter was rained on. Arizona fescue, douglas fir, ponderosa pine and aspen were collected by others and we do not know what methods were used.  All litters were sorted and damaged material or reproductive parts were discarded. Unless previously dried, litter was air-dried in the laboratory. Litter bags consisted of coated fiberglass window screen material cut into 12 by 7.5 sheets, which were folded in half and two of the edges folded over and stapled. Litter was inserted through the unstapled edge, which then was folded over and stapled. Each bag initially contained 5.00 g (4.95-5.05 g) of air-dried material. For each litter type, a total of 34 bags were prepared for placement at each location. All the litter bags of one species for an individual location were placed in a separate bag and the bag was sealed for transport the field.

At each location and for each species, the experimental design included placement of enough litter bags for three replicate bags per collection date; one collection at the time of placement, eight collections over a two year period, and 7 additional bags to allow for some mortality of bags (34 bags total per location).

When the litter bags were placed at each location, the location was marked with fence posts as a warning. Each location was identified by a color-coded marker. The color-coded markers for each location are as follows: location (1)=plain, (2)=tan, (3)=green, (4)=orange, (5)=orange/green, (6)=tan/green, (7)=green/tan, (8)=green/orange, and (9)=tan/orange.

Litter bags were placed on bare soil between plants at all times. Each litter bag was anchored by inserting a 16 penny nail through diagonal corners of the bag and into the ground.  Decomposition bags with creosote, blue grama, yucca (tethered, not bagged), and four-wing saltbush all were placed at the deep well location (location 2); and cottonwood at the Bosque del Apache (location 8).

In the fall of 1990, only 5 litter types (black grama, blue grama, juniper, creosote, and Indian ricegrass) were collected for placement in Feb. of 1991. Blue grama litter was only placed       at Deep Well, while the four other litter types were place at 4 locations (#2, 7, 10, 11). Litter was collected as described in the previous year and bags were placed on bare soil at each location.

In February of 1999, the Rio Salado and Red Tank sites did not get new litter bag placements; instead the new locations at Blue Springs and 5 points were established and the 4 common litter types were placed at these locations along with Deep Well and Cerro Montoso.

Sample Collection Methods:

For each individual location collection, three replicate bags are placed in zip-lock bags and are identified by species, field location, collector initials, and date of collection. A general maintenance survey of each location is done at this time by the collector(s). At the time of placement, three bags of each species were collected and placed into a gallon-sized zip-loc bag for transport to the lab. This method insured that each replicate was handled the same way with bouncing during transport and sample handling consistent for all samples. These three samples taken at the time of placement determine the starting (incubation in the field time 0) replicate litters. For each collection date, 28 gallon-size zip-lock bags were be needed.

Sample Analysis Methods:

Overview: 

Handling of the field samples involves three phases: (1) initial cleaning and oven-dry weight; (2) grinding and ash correction; and (3) chemical analyses. Once in the laboratory, field samples will come in with 3 replications/plant type in a bag labelled with the site, plant material, and collection date. In Phase 1, the samples are cleaned, oven dried at 60° C for a minimum of 24 hours, and oven-dry weight recorded. The  samples are then transferred to coin envelopes, ground on the Tecator grinder, and stored back in the coin envelope. In Phase 2, ground plant material is then used for ash-free weight determinations. In Phase 3, the remaining ground plant litter is used for chemical analyses.

Phase 1. 

WEIGHING 

1.  A zip-loc bag with field samples  is selected to begin weighing out. One mesh bag is selected and  this sample was arbitrarily assigned as a replicate number and Sample ID number. Any foreign material was removed from the outside of the bag, such as: differen plant material, mud, ROCKS, etc, making sure to lift up the side folds to release any trapped rocks.  The weighed and labelled weigh boat was placed on a sheet of paper and the contents of the bag were emptied into the weigh boat. This was repeated for all samples and the samples were placed in the oven. 

2.  Samples were dried for a minimum of 24 hours at 60° C. Samples were weighed and weights were recorded in the record book.  Samples were then placed into a coin envelope labelled with the collection date, site number, plant type, and Sample ID number.

GRINDING 

Plant material was ground in order to perform ash-free weight corrections and chemical  analyses. The only plant material needed to be ground using liquid N were: pinyon, juniper and creosote. All others were ground warm.

Phase 2. 

ASH-FREE WEIGHT CORRECTION METHOD 

Methods 1989 through 1991: 

ASH THE EMPTY CRUCIBLES: Line up a sufficient quantity (about 40) of the tall, narrow, numbered porcelain crucibles. Wipe them out with a Kimwipe. Load them into the muffle furnace making sure not to touch the oven sides or each other. Use the shelf to fit them all in. Close the muffle furnace. Turn on the exhaust fan. Turn the controller to 5.0, and turn the timer to 2 hours. After about 1.5 - 1.75 hours, check to verify that the temperature has or will reached 500 °C.  If it hasn't, add additional time to the controller. When it does hit 500 °C, it is hot enough and ready to shut off. Let cool, closed, overnight. The next day the crucibles can be removed and stored in a desiccator.

DRY THE GROUND MATERIAL: The ground material in their envelopes  was placed in a 60 °C oven for 24 hours prior to weighing out for ashing. When the crucibles are thoroughly cooled, weigh the empty crucible and then place out approximately 1 gram using the analytical balance (BE SURE TO MIX THE SAMPLE WELL BECAUSE PARTICLES TEND TO SEPARATE DURING STORAGE AND HANDLING) of ground material into the crucible, and then record the filled crucible weight on the data charts in the front of this book. Remember to weigh and include a blank (empty) crucible with each run.

ASH THE WEIGHED SAMPLE:  Using tongs, load the crucibles into the muffle furnace, making sure not to touch the oven sides or each other. Use the shelf to fit them all in. Close the muffle furnace. Turn on the exhaust fan. Turn the controller to 5.0, and turn the timer to 2 hours. After about 1.5 - 1.75 hours, check to verify that the temperature has reached 500 °C. If it hasn't, add an extra 15 minutes to the timing. When it does hit 500°C, and the timer has turned off the furnace, turn the controller to 2.0, and the timer to 2 hours. Let cool, closed, overnight.

WEIGH THE ASHED SAMPLES: Using tongs, remove the crucibles to a desiccator. When they are thoroughly cooled, use the same analytical balance and record the filled crucible weight on the data charts in the front of this book. Remember to weigh and include the blank (empty) crucible from each run. Dump out the ashed sample into the garbage, wiping the crucible with a Kimwipe if necessary. The crucibles are now ready to be filled again and fired. 

Methods after 1991: 

Ashing methods were changed in 1991 when the use of porcelain crucibles was replaced by use of disposable aluminum boats. All methods stayed the same EXCEPT: The disposable aluminum boats did not need to be 'tared' or fired before use. The clean boats were taken directly from the package and placed into use. To identify the boat, the SAMPLE ID # was 'written' (etched indented with a pencil-pen) on the bottom of the boat. The boat weight was recorded and the sample (WITH MIXING!) was added (about 1 gram). The rest of the procedures remained the same. If the muffle furnace was allowed to exceed 550 °C, the aluminum boats would melt and significant changes in their weight could occur. Blank boats are run with each operation to insure no significant loss-gain during firing.

Analytical Methods Used:

Kjeldahl Nitrogen and Phosphorus by Technicon Industrial Method No. 369-75A (Revised 8/21/75) Digestion and sample preparation for the analysis of total kjeldahl nitrogen and/or phosphorus in food and agricultural products using the technicon BD-20 Block digestor and Technicon Industrial Method 334-74A (revised 8/21/75) Individual/simultaneous determination on nitrogen and phosphorus in BD acid digests.

Percent Nitrogen and Percent Carbon were determined by High Temperature combustion, the resulting gases were eluted on a gas chromatography column and detected by thermal conductivity and integrated to yield carbon and nitrogen content.  Analyses were performed on a ThermoQuest CE Instruments NC2100 Elemental Analyzer, ThermoQuest Italia S.p.A., Rodano, Italy.  

Instrumentation: 

Study Instrumentation: ThermoQuest CE Instruments, NC2100, Elemental Analyzer (Nitrogen and Carbon).

Additional information: 

Site Name:: Location 1, Black Butte

Site Location: SW of gate on east side of black butte (north border of east side)

Site Coordinates: 34.40667735, -106.68647480, NAD83

Site Size: 5 x 5 m

Site Elevation: 1560.2 m

Site Soil: sandy

Site Name:: Location 2, Deep Well

Site Location: deep well, east side

Site Coordinates: 34.35277814, -106.69230409, NAD83

Site Size: 5 x 5 m

Site Elevation: 1605.07 m

Site Vegetation: black and blue grama

Site Name:: Location 3, Old 5 points

Site Location: 1 mile east-southeast of 5 points

Site Coordinates: 34.27395094, -106.67859413, NAD83

Site Size: 5 x 5 m

Site Elevation: 16.92.34 m

Site Name:: Location 4, Larrea

Site Location: between location 3 and the south boundary

Site Coordinates: 34.24100599, -106.74927778, NAD83

Site Size: 5 x 5 m

Site Elevation: 1617.05 m

Site Vegetation: Creosote

Site Name:: Location 5, Ocotillo

Site Location: Near south boundary

Site Coordinates: 34.22190529, -106.70410020, NAD83

Site Size: 5 x 5 m

Site Landform: south facing slope

Site Elevation: 1723.05 m

Site Vegetation: Ocotillo

Site Name:: Location 6, Sepultura Canyon

Site Location: Sepultura Canyon

Site Coordinates: 34.30220417, -106.62011595, NAD83

Site Size: 5 x 5 m

Site Landform: foothills of the Los Pinos

Site Elevation: 1872.44 m

Site Vegetation: grass-juniper savannah

Site Name:: Location 7, Cerro Montoso

Site Location: Cerro Montoso

Site Coordinates: 34.36851996, -106.53503075, NAD83

Site Size: 5 x 5 m

Site Elevation: 1970.74 m

Site Name:: Location 8, Bosque del Apache

Site Location: Bosque del Apache NWR, east side of Rio Grande

Site Coordinates: 

Site Size: 5 x 5 m

Site Vegetation: riparian forest

Site Name:: Location 9F, Magdelena Mountains Forest

Site Location: Magdelena Mountains, west of Socorro

Site Coordinates: 33.98152914, -107.18597909, NAD83

Site Size: 5 x 5 m

Site Elevation: 3187.6 m

Site Vegetation: High elevation forest-meadow

Site Name:: Location 9M, Magdelena Mountains Meadow

Site Location: Magdelena Mountains, west of Socorro

Site Coordinates: 33.99204766, -107.17438462, NAD83

Site Size: 5 x 5 m

Site Elevation: 3033.6 m

Site Vegetation: High elevation forest-meadow

Site Name:: Location 10, Rio Salado

Site Location: Rio Salado

Site Coordinates: 34.29572804, -106.92662418, NAD83

Site Size: 5 x 5 m

Site Elevation: 1509.54 m

Site Soil: sandy soil

Site Vegetation: Chihuahua desert with creosote dominant

Site Name:: Location 11, Red Tank

Site Location: Red Tank, in foothills of ladrone Peak

Site Coordinates: 34.39791210, -107.03647141, NAD83

Site Size: 5 x 5 m

Site Elevation: 1767.12 m

Site Vegetation: Great Basin grass-shrub

Site Name:: Location 12, Blue Springs

Site Location: Blue Springs, (lower goat draw), northeast corner of SNWR

Site Coordinates: 

Site Size: 5 x 5 m

Site Vegetation: grass-juniper savannah

Site Name:: Location 13, 5 points

Site Location: east of actual road junction near site of grassland-creosote webs

Site Coordinates: 34.33272200, -106.73100528, NAD83

Site Size: 5 x 5 m

Site Elevation: 1613.89 m

Site Vegetation: creosote

Description of Initial Study: 

The decomposition study began with litter grown during 1989, which was harvested in the fall of1989, prepared during the winter and placed in the field the following spring. The initial study was designed by Dr. J. Gosz and Dr. R. Parmenter with C.S. White the project manager. The basic design included placement of three (3) primary litter-types (black grama (Bouteloua gracilis), juniper (Juniperus monosperma), and Indian       rice grass (Oryzopsis hymenoides)) at seven (7) locations. The seven locations included: along an approximate north-south transect from grass habitat to creosote habitat, Location 1 = Black Butte; Location 2 = Deep Well; Location 3 = 1 mi. east of 5 points (central point along the transect representing a grass-juniper-creosote junction); Location 4 = between Location 3 and south boundary within a creosote stand (Larea); and Location 5 = south boundary at a stand of Ocotillo (Ocotillo); and along an approximate east transect from location 3; Location 6 = Sepultura Canyon; and Location 7 = Cerro Montoso (increasing favorable juniper habitat and into pinyon). There were two other locations off the Sevilleta NWR in the first year: Location 8 at the Bosque del Apache (which later was lost during a fire at that location); Location 9 in the Magdelena Mountains west of Socorro.

At all locations (except Bosque del Apache), litter of the three common species were included. Litter of different species were placed at locations where that litter may be dominant. The other litter types included: creosote (locations 2 and 4), blue grama (location 2), 4-wing saltbush (location 2), yucca (location 2), pinyon (location 7), cottonwood (location 8); and Arizona fescue, Douglas fir, Ponderosa pine, and aspen (location 9).

At each location and for each species, the experimental design included placement of enough bags for three replicate bags per collection date; one collection at the time of placement and eight additional collections over a two year period, and 7 additional bags to allow for some mortality of bags (34 bags total). Each bag initially contained 5.00 g +/- 0.05 g (4.95-5.05g) air-dried material. Bags were placed at each location in late February, 1990. Collections are projected to be made in: (1), May 1990 (2), July 1990 (3), Sept. 1990 (4), January 1991 (5, one-year), May 1991 (6), Sept 1991 (7), and January 1992 (8, two-year).

Changes in 1990: 

In 1990, litter was only placed at the Deep Well location (#2) and only litters of black grama, juniper, rice grass, creosote, blue grama and saltbush were used. It was decided that all the sites were not worth continuing because there were no other data associated with the site that could be used to explain why decomposition may or may not vary at that site versus and other site. Thus, the location with the most complete meteorological data was maintained (Deep Well, location 2).

Changes 1991 through 1998: 

Starting with litter collected in the fall of 1991 and continuing through litter collected in 1997, litter bags were placed at four (4) locations that represented the range of climates present on the Sevilleta and that were all near meteorological stations. Deep Well (location 2) and Cerro Montoso (location 7) were retained from the previous work because they were near meteorological stations. Cerro Montoso (location 7) represented a      pinyon-juniper forest, upper elevation climate (wettest of all locations), Deep Well (location 2) represented a short-grass prairie climate, a location near the Rio Salado (new, location 10) represented a Chihuahuan desert climate (driest of all locations), and Red Tank (new, location 11) represented a Great Basin grass-shrub climate. Deep Well and Cerro Montoso (location 1 and 7, respectively) are on the east side of the Sevilleta while Rio Salado and Red Tank (locations 10 and 11, respectively) are on the west.

At these four locations, black grama, creosote, Indian rice grass, and juniper litter were placed every spring. Blue grama litter also was placed at Deep Well to maintain a long-term blue and black grama comparison.

Changes in 1998: 

Beginning with placement of litter collected in the fall of 1998, efforts to conserve resources and to address changes across vegetation transition zones lead to addition of 2 new locations: Blue Springs (location 12), a juniper-short grass prairie mixture; and 5 points (location 13), a creosote area near the Deep Well short grass-desert grass area. No new litter was placed at Rio Salado and Red Tank (locations 10 and 11), but remaining     litter were collected for the 1 year decomposition measurement in Feb. of 1999 and will be collected again in Feb. of 2000 for the two year decomposition measurement. The four common litter types were placed at Cerro Montoso, Blue Springs, Deep Well, and 5 points (locations 7, 12, 2, and 13, respectively) with blue grama also at Deep Well.

Study Personnel: James R. Gosz; Carl White; John Craig; Doug Moore; John Dewitt; Todd Haagenstad; Lisa Apodoca; Erica Barner; Micky Boise; Kavita Patel; Steve Hofstad, Tze Sun Yong; Luis Guzman; Chris Thomas; David Wales; Kerry Carr; Deb Sena; Olivia Hopkins 

Small Mammal Exclosure Study (SMES) Leaf Litter Study in the Chihuahuan Desert Grassland and Shrubland at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time?

This is data for cover of dead plant leaf litter accumulations on soil surfaces measured on each of the SMES study plots. Leaf litter cover was measured from each of the 36 one-meter2 quadrats twice each year when vegetation was measured.

Core Areas: 

Data set ID: 

96

Additional Project roles: 

122
124

Keywords: 

Data sources: 

sev096_smeslitter_20160308.csv

Methods: 

Experimental Design:

There are 2 study sites, the Five Points grassland site, and the Rio Salado creosotebush site. Each study site is 1 km by 0.5 km in area. Three rodent trapping webs and four replicate experimental blocks of plots are randomly located at each study site to measure vegetation responses to the exclusion of small mammals. Each block of plots is 96 meters on each side. Each block of plots consists of 4 experimental study plots, each occupying 1/4 of each block. The blocks of study plots are all oriented on a site in a X/Y coordinate system, with the top to the north. Treatments within each block include one unfenced control plot (Treatment: C), one plot fenced with hardware cloth and poultry wire to exclude rodents and rabbits (Treatment: R), and one plot fenced only with poultry wire to exclude rabbits (Treatment: L). The three treatments were randomly assigned to each of the four possible plots in each block independently, and their arrangements differ from block to block. Each of the three plots in a replicate block are separated by 20 meters.

Each experimental measurement plot measures 36 meters by 36 meters. A grid of 36 sampling points are positioned at 5.8-meter intervals on a systematically located 6 by 6 point grid within each plot. A permanent one-meter by one-meter vegetation measurement quadrat is located at each of the 36 points. The 36 quadrats are numbered 1-36, starting with number 1 in the top left corner (north-west) of each plot (top being north), and running left (west) to right (east), then down (south) one row, and then right (east) to left (west), and so on Quadrat/rebar number one is in the northwest corner of each plot, and numbers 1-6 are across the north side of the plot west to east, then quadrat/rebar number 7 is just south of quadrat/rebar number 6, and rebar numbers increase 7-12 east to west, and so on. 3-inch nails were originally placed in the top left(north-west) corner of each quadrat. These may be difficult to see. A 3-meter wide buffer area is situated between the grid of 36 points and the perimeter of each plot.

While measuring vegetation on each quad, the total amount of leaf litter cover on the soil surface that was seen on each quadrat was measured. "Leaf litter cover(n)" for the cover of leaf litter on the soil surface of the quadrat was stated in terms of the 10 cm squares. For cover values less than 5, increments of 1.0 were used. For cover values greater than 5, increments of 5.0 were used. Leaf litter included all detached dead plant material on the soil surface, including woody branches. Only leaf litter cover that is in the open was measured, not within clumps of grass, etc. Some leaf litter cover had distinctive margins and was easy to define and measure. However, much leaf litter consisted of many diffuse small patches that are separated by bare soil, and distributed throughout the quadrat. For such diffuse cover, the actual cover in one typical 10 by 10 cm square (e.g., 0.3) was determined, the number of squares with diffuse cover (e.g., 5) was counted, then the number of squares was multiplied by the actual cover for a typical square (e.g., 0.3 X 5 = 1.5, then round to 1.0 or 2.0, or if the value had been greater than 5, round to the nearest increment of 5.0) for the total litter cover. All litter cover was pooled into one observation, and no height was measured.

Maintenance: 

SEVILLETA SMES LEAF LITTER DATA 1998 log Updat03/09/06 Status DONE 01/31/06 - Checked data for missing data points, doubles, and errors. Missing data points were recorded using -999 (Human Error) or -888 (-888), duplicates of data points were removed, and errors were corrected. If a data point contained a measurement and a measurement with a count, the zero observation was removed. - Removed Species, and Per fields. Tape field was changed to ID# and observations made in the Per field were moved to the new ID# field. No observations were made in the tape field. EC field was added and NA was recorded in this field for this year. Date MM/DD/YY field was changed to just DATE. Other changes in the fields include PLT to PLOT, BLK to BLOCK, and SPECICOV to COVER. - Any empty cells were filled in with -999 (or -888) for missing data or an NA for not applicable. - Yang Xia 02/24/06 - Checked data for missing data points, doubles, and errors. Missing data points were recorded using -999 (Human Error) or -888 (-888), duplicates of data points were removed, and errors were corrected. If a data point contained a measurement and a measurement with a count, the zero observation was removed. - Removed Species, Comments, and Per fields. Tape field was changed to ID# and observations made in the Per field were moved to the new ID# field. No observations were made in the tape field. EC field was added and NA was recorded in this field for this year. Date MM/DD/YY field was changed to just DATE. Other changes in the fields include PLT to PLOT, BLK to BLOCK, and SPECIcOV to COver. - In the spring, Missing all Plots for Block 1 at the Grassland site. There are missing data in Site G Block 2 Plot 3 Treatment C, Site G Block 3 Plot 3 Treatment R, and Site G Block 4 Plot 2 Treatment C. - For the fall, All plots are presented, but with several data points missing. - Any empty cells were filled in with -999 (or -888) for missing data or an NA for not applicable. - Yang Xia 03/03/06 - Changed data to fit parameters. For example if a measurement was 6 it was rounded to the closest appropriate value, which in this case is 5. See 'Variable Descriptions' Variable 7. Also, if a measurement was less than 0.5 it was rounded to 1 to indicate that an occurence was present. - Yang Xia 03/06/06 - Quads 21-24 were originally classified as Trt C in the spring at the Grass site for Blk 4 Plt 3, Changed to Trt L. - Quads 10-17 were originally classified as TRT C in the spring at the Creosote Site for BLOCK 2 PLOT 2, changed the TRT to TRT L. - Quads 11-14 were originally classified as TRT C in the spring at the Creosote Site for BLOCK 3 PLOT 4, changed TRT to TRT L. 03/08/06 - Modified metadata to correct format. - Yang Xia 03/09/06 - changed EC variable data to "1" with the comments, and "0" for no comments. NA for not applicable. 03/09/06 - changed start date from september 1995 to May 1995 in the research Hypotheses, since the data collection was starting on 05/02/95. doc

Additional information: 

Additional Information on the personnel associated with the Data Collection / Data Processing

Sevilleta Field Crew Employee History

Megan McClung, April 2013-present, Stephanie Baker, October 2010-Present, John Mulhouse, August 2009-Present, Amaris Swann, August 25, 2008-January 2013, Maya Kapoor, August 9, 2003-January 21, 2005 and April 2010-March 2011, Terri Koontz, February 2000-August 2003 and August 2006-August 2010, Yang Xia, January 31, 2005-April 2009, Karen Wetherill, February 7, 2000-August 2009, Michell Thomey, September 3, 2005-August 2008, Jay McLeod, January 2006-August 2006, Charity Hall, January 31, 2005-January 3, 2006, Tessa Edelen, August 15, 2004-August 15, 2005, Seth Munson, September 9, 2002-June 2004, Caleb Hickman, September 9, 2002-November 15, 2004, Heather Simpson, August 2000-August 2002, Chris Roberts, September 2001-August 2002, Mike Friggens, 1999-September 2001, Shana Penington, February 2000-August 2000.

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