Transect Leaf-litter Microarthropod Data

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*Changes in microarthropod assemblages were monitored in six types of decomposing surface leaf-litter confined in mesh bags and set across a Chihuahuan Desert watershed for 17 months. The following hypotheses were tested: 1) microarthropod density and diversity are higher in soils with maximum surface litter accumulation, and 2) temporal patterns of density and diversity are more dependent on seasonal factors and physical disturbances than on the decompositional stage of the litter.

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Field data sheets

*I studied surface leaf-litter decomposition of the following species, which are common in one or more of the zones of the watershed: vine mesquite grass (Panicm obtusum), mesquite (Prosopis glandulosa), desert marigold (Baileya multiradiata), creosotebush (Larrea tridentata), fluffgrass (Erioneuron pulchellum), and black grama grass (Bouteloua eriopoda). Leaves (creosotebush and mesquite) and aboveground parts (vine mesquite grass, desert marigold, fluffgrass, and black grama grass) were picked up or chopped in fresh condition from standing plants, during July 1984, and sun-dried for about a week. The drying material was daily turned over to assure homogeneous desiccation. Then it was seived and cleaned of soil particles and large pieces of plant tissues. Litter bags (15 by 15 cm) were constructed from fiberglass mesh (1.5 mm) or aluminum mesh (close to 1.5 mm). Every bag was filled with 10.35 plus/minus 0.15 g of air-dried litter. 930 pairs of these litter-containers were apportioned on the six lower vegetation zones (155 pairs per zone). Aluminum bags replaced the original fiberglass bags in the playa site after these were destroyed by an unknown agent, possibly crickets. Pairs of bags, fastened to the soil surface by 8cm nails, were placed under the canopy or close to plants belonging to the site-dominant species, namely: vine mesquite grass (playa), mesquite (playa fringe), snakeweed (basin slope), creosotebush (bajada), fluffgrass (lower piedmont), and black grama grass (upper piedmont). The pairs were formed by combining one mesh-bag containing crosotebush litter, and one enclosing site-dominant leaf-litter. On each site, the bags were distributed on both sides of the control transect, and dispersed over a small area (no larger than 30 by 20 m). Immediately after setting the litter bags, I took a random sample of five pairs per site to estimate moisture content and spillage due to handling. Fluffgrass and crosotebush leaf-litter exhibited the largest losses (wet weight) due to handling; moisture content, in turn, was higher in creosotebush and vine mesquite grass. Litter bags were retrieved biweekly in the growing season and monthly during the remaining time. On each sampling date, five randomly selected pairs of bags per site were retrieved within 3 hours after sunrise, placed in plastic bags, and carried to the laboratory in refrigerated containers. Simultaneously, five soil cores (5 cm diameter by 10 cm depth) were taken from the mineral soil underlying the litter bag with site-dominant litter-type. The content of the retrieved samples was kept for 48 hours in light-heat extractors for microarthropod isolation in the laboratory. The litter was then oven-dried at 60C for a minimum of five days, weighed and ashed in a muffle furnace. Sampling covered a period of 17 months, from August 1984 to December 1985. A total of 22 sets of samples was collected throughout the study. Each set comprised 60 litter-bags and 30 soil cores. Representative microarthropods were mounted on microscope slides for reference. Taxonomic identification to lower categories (genus or species) was conducted with the most abundant groups.

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In the spring of 1982, as part of the establishment of the Jornada Long-Term Ecological Research site in southern New Mexico, a 135 ha portion of a 1500 ha, internally drained, watershed was exclosed from grazing by domestic livestock. Prior to exclosure the watershed, as well as the rest of the Jornada basin, had been moderately to heavily grazed for the past 100 years. Concurrent with grazing, the vegetation had undergone a dramatic change from desert grassland, with an almost continuous cover of C4 perennial grasses, to isolated patches of the original grassland in a mosaic with desert shrub dominated plant communities (Buffington and Herbel, 1965). The exclosure lies along a northeast facing piedmont slope at the base of a steep isolated mountain peak, and covers a variety of component landforms from the foot of the mountain to the basin floor. The northeast side of the exclosure is immediately upslope of the College Playa located near the NMSU College Ranch. Three parallel transects (2.7 km in length) run from the middle of the College Playa up into the foot of Mt. Summerford. The Control transect is to the west, the Treatment transect on the east side of the Control transect, and the Alternate Control to the east of the Treatment transect. Each transect is 30 meters wide with a 45 meter buffer zone between each transect. Only the control transect was used in this study.


Bi-weekly during growing season (Jul-Sept); Monthly at all other times

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