Snakeweed (Gutierrezia sarothrae) Habitat Soils Data from the Sevilleta National Wildlife Refuge, New Mexico (1984)


In 1984, a research project was initiated on a relatively small disturbance patch just south of Deep Well. This disturbance was thought to be the result of an old praire dog town, probably dating back to when a nearby ranch was active, and a lot of old mammal mounds remained in the disturbed area. One of the things that made the disturbance patch particularily noticeable was the lush growth of snakeweed (Gutierrezia sarothrae) within the patch. This prompted the designation of the disturbance patch as the "snakeweed patch" or "Gutierrezia patch." In addition, there was an obvious increase in bare ground and a shift in vegetation composition across the patch boundary. The dominant vegetation was not consistent around the boundary, with a marked dominance of black grama on the west side of the plot and a blue/black grama mix on the other three sides. To obtain information on the cause and/or effect of this disturbance, a survey of the soil and vegetation was performed.

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Sample collection - The soil samples were collected using a hammer-driven soil corer. The barrel of the corer was fitted with a plastic sleeve that allowed extraction of the soil core generally intact. The  soil corer was driven to a depth of 50 cm and soils split ito 10 cm fractions. This data set contains data for only the top 30 cm.

Samples were taken along six 100 m transects. Four of these transects crossed the patch boundary on the four cardinal points. On these four transects the 0m sample was taken starting 50 m outside the boundary, the 50 m sample was taken at the patch boundary and the 100 m sample was taken 50 m into the patch. The other two transects formed a cross near the center of the patch.

Twenty-one cores were collected along each transect, with increased sampling intensity near the boundary. However, this data set contains data from only the 10 m intervals for a total of 11 samples.

Sample processing - Soil samples were kept in a refrigerator prior to analysis. Each sample was weighed and samples were well-mixed before analysis. Samples were sieved through 2mm screens to remove pebbles and roots. A sample of 25 g was added to a preweighed soil can. Samples were dried for 24 hours at 105 degrees C then cooled and then reweighed. This dry/wet moisture correction was used to calibrate weights for other samples. A 1 g sample was taken from the oven-dried samples and ashed at 500 degrees C for 2 hours and re-weighed after cooling. This provided a measure of organic content. A 12 g sample was weighed into a 125 ml plastic bottle and 100 ml of 2 N KCL added before the bottles were well-shaken. After standing for 24 hours, the KCL was decanted and the samples analyzed for NO3-N and NH4-N on a Technicon Autoanalyzer. Another 5 g sample was weighed into a centrifuge tube and extracted repeatedly with pH 7 ammonium acetate. These samples were brought up to 250 ml and analyzed for Ca, Mg and K using atomic absorption. Fifty g samples of soil were mixed and texture determined using the hydrometer method. Samples were mixed 2:1 with 0.001N CaCl2 and pH measured. From the oven-dried samples 1 g samples were digested using sulfuric acid using the Kjeldahl method. Samples were then brought up to 250 ml and analyzed on a Technicon Autoanalyzer for total nitrogen and phosphorous.

Coordinates (NAD27): 

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Transect Transect Latitude Longitude

North 0 34 21' 1.2" 106 41' 8.3"W

100 34 20' 57.9"N 106 41' 8.6"W

East 0 34 20' 47.0"N 106 41' 1.6"W

100 34 20' 46.5"N 106 41' 5.4"W

West 0 34 20' 53.7"N 106 41' 16.3"W

100 34 20' 53.7"N 106 41' 12.4"W

GCSA 0 34 20' 49.1"N 106 41' 9.2"W

100 34 20' 45.6"N 106 41' 9.2"W

GCSB 0 34 20' 47.1"N 106 41' 8.9"W

100 34 20' 47.4"N 106 41' 5.1"W


12/10/00 (DM) File created.2/10/2009. (DM) Metadata was updated and compiled.

Soil Characteristics Following a Lightning-Initiated Fire at MacKenzie Flats, Sevilleta National Wildlife Refuge, New Mexico (1998)


We evaluated soil characteristics after a lightning-initiated fire. Following the fire in July 1998, 25 experimental plots were established on the eastern edge of MacKenzie Flats at the Sevilleta National Wildlife Refuge. Ten of these plots were located in a Bouteloua gracilis (blue grama)-dominated site, while 15 were established in another area dominated by Bouteloua eriopoda (black grama). All plots were oriented along a topographic gradient that ran in an east-west direction. At three topographic locations within each plot, soil samples were taken at two depths from an area covered by perennial grass as well as an area devoid of vegetation. Soil samples were collected in July 1998 and analyzed for moisture content and soil texture.

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Experimental Design - Following a lightning-initiated fire in July 1998, 25 experimental plots were established on the eastern edge of the MacKenzie Flats area of the Sevilleta National Wildlife Refuge. Ten of these plots were located in a Bouteloua gracilis (blue grama)-dominated site, while 15 were established in another study area, where B. eriopoda (black grama) was more abundant. In the former site, five of the 10 plots were established in burned areas, and the others were positioned in unburned grassland vegetation. In the latter study area, five plots were placed in burned areas, five were positioned in unburned grasslands, and the five remaining plots were located in an area that contained a mix of burned and unburned patches of grassland vegetation.

Sampling Design - All of the plots in the Bouteloua gracilis-dominated site were 4 m x 16 m in dimension. Of the 25 plots where B. eriopoda was more abundant, nine were 4 m x 16 m, and 16 were 4 m x 25 m. Regardless of site, all plots were oriented such that the long axis of each was parallel to a topographic gradient that ran in an east-west direction.

We established three 1.5 m x 1.5 m quadrats at the two corners and midpoint along the south side of each plot. Each quadrat was divided into four square cells of equal area. Within a southeastern cell (northeastern cell if a shrub was present in a southeastern cell), we selected three grass clumps and three interspace areas between plants. At the center of each plant and interspace, one sample was removed at each of two depths (0 - 2.5 cm and 2.5 - 10cm). The three "grass" samples at each depth were pooled to create one composite sample; similarly, the three interspace samples at each depth were also pooled into one sample (4 composite samples in total).

Field Methods - For the 0 - 2.5 cm samples, a 2.5-cm corer (6.7 cm diameter) was driven into the ground with a mallet. Over grass clumps, the corer was inserted such that the average original soil surface was flush with the top of the corer, generally at about one-half the height of the tussock. A sharpened trowel was hammered beneath the corer to cut the roots, and the core was removed. Any soil which fell onto the new surface was scraped away.

For the 2.5 - 10 cm samples, a 25-cm corer (4.5 cm diameter) was driven to a depth of 7.5 cm below the surface created by the previous sample. The corer was then twisted and gently pulled up. The average point of break for any individual core was estimated to be within 1 - 2 mm for at least 90% of the cores.  The soil was resampled if this error exceeded 3 mm.

Samples were placed into pre-labeled paper lunch bags and transferred to a cooler (without ice). They were transported to a drying shed with ambient temperature and humidity and placed on shelves within 36 hours.

Laboratory Procedures - Soil moisture was determined by the gravimetric method (Gardner 1986). Soil texture was determined by the hydrometer method (Sheldrick and Wang 1993).

Gardner, W. H. 1986. Water content. Pages 493-544 in A. Kluite (editor), Methods of soil analysis, Part 1. Physical and minerological methods, agronomy monograph no. 9, 2nd edition. American Society of Agronomy and Soil Science Society of America, Madison, WI.

Sheldrick, B.H. and C. Wang. 1993. Particle size distribution. Pages 499-557 in M.R. Carter (editor), Soil sampling and methods of analysis. Canadian Society of Soil Science, Lewis Publishers, Ann Arbor, MI.

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