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 perennial plant vegetation canopy cover measured from all SMES study plots, fall 1995 and fall 2005. The purpose of this data is to provide ground-truth data for comparison with low-level aerial photographs of each study plot. Three, 29 meter lines were measured along three of six rows of the permanent vegetation measurement quadrats. Each line was measured at 10cm resolution for intercepts of perennial plant live canopy cover, and for bare ground. 10cm resolution is comparable to the resolution of the aerial photos. All plants were identified to the species level. These line-intercept measurements are taken once every ten years, at the same time that low-level aerial photographs are taken. These data will be compared to both decadal air photos, and annual measures ofvegetation from one-meter2 quadrats on each plot to provide information on vegetation change over time relative to the various animal exclosure treatments.
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 ofeach 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.
How Data Were Collected:
100 meter measuring tapes were attached to the steel re-bar posts marking vegetation quads 1, 3, and 5 on each study plot. The measuring tapes were extended south to the re- bar posts marking quads 36, 34, and 32. Data were recorded for all intercepts of live perennial plant canopy foliage, and for bare ground. The start and end points for each intercept were recorded to the nearest 10 cm on the measuring tape. Intercepts less than 5 cm were ignored, and intercepts between 5 and 10 cm were recorded to the nearest 10 cm. Intercept measurements were only recorded for perennial plant species, and for bare soil. Annual plants and dead perennial plants were ignored.
April 9, 2002: File created by Kristin Vanderbilt.Updated by Karen Wetherill, January 4, 2006. In 2006, the 1995 data codes were updated to reflect current Kartesz codes as found on the USDA plants website. In particular ATCA to ATCA2, ERPU to DAPU7, HIJA to PLJA, MAUR2 to MUAR2, MUPO to MUPO2, OPPH to OPPHP, SATR12 to SATR12, SCBR to SCBR2, SEMU to SEMU2, SPFL to SPFL2. Codes that could not be decipher and are still in the data set are LEER, OPVI, SCPO (could be SCPA6), and SPUK. Other mistakes such as site=L for Larrea were change to site= C. Negative intercepts (4) were NOT corrected.
The data were entered in the field on to micro-cassette tape recorders. The taped recorded data were then entered on to MS Excel spreadsheets. A macro statement was used to subtract each observed intercept end measure from the start measure, to produce an intercept measure for each observation. Those data were then converted to space-formatted text files, and combined as one file. In 2006, the 1995 data codes were updated to reflect current Kartesz codes as found on the USDA plants website.