Humans are creating significant global environmental change, including shifts in climate, increased nitrogen (N) deposition, and the facilitation of species invasions. A multi-factorial field experiment is being performed in an arid grassland within the Sevilleta National Wildlife Refuge (NWR) to simulate increased nighttime temperature, higher N deposition, and heightened El Niño frequency (which increases winter precipitation by an average of 50%). The purpose of the experiment is to better understand the potential effects of environmental drivers on grassland community composition, aboveground net primary production and soil respiration. The focus is on the response of two dominant grasses (Bouteloua gracilis and B eriopoda), in an ecotone near their range margins and thus these species may be particularly susceptible to global environmental change.
It is hypothesized that warmer summer temperatures and increased evaporation will favor growth of black grama (Bouteloua eriopoda), a desert grass, but that increased winter precipitation and/or available nitrogen will favor the growth of blue grama (Bouteloua gracilis), a shortgrass prairie species. Treatment effects on limiting resources (soil moisture, nitrogen availability, species abundance, and net primary production (NPP) are all being measured to determine the interactive effects of key global change drivers on arid grassland plant community dynamics and ecosystem processes. This dataset shows values of soil moisture, soil temperature, and the CO2 flux of the amount of CO2 that has moved from soil to air.
On 4 August 2009 lightning ignited a ~3300 ha wildfire that burned through the experiment and its surroundings. Because desert grassland fires are patchy, not all of the replicate plots burned in the wildfire. Therefore, seven days after the wildfire was extinguished, the Sevilleta NWR Fire Crew thoroughly burned the remaining plots allowing us to assess experimentally the effects of interactions among multiple global change presses and a pulse disturbance on post-fire grassland dynamics.
Our experimental design consists of three fully crossed factors (warming, increased winter precipitation, and N addition) in a completely randomized design, for a total of eight treatment combinations, with five replicates of each treatment combination, for a total of 40 plots. Each plot is 3 x 3.5 m. All plots contain B. eriopoda, B. gracilis and G. sarothrae. Our nighttime warming treatment is imposed using lightweight aluminum fabric shelters (mounted on rollers similar to a window shade) that are drawn across the warming plots each night to trap outgoing longwave radiation. The dataloggers controlling shelter movements are programmed to retract the shelters on nights when wind speeds exceed a threshold value (to prevent damage to shelters) and when rain is detected by a rain gauge or snow is detected by a leaf wetness sensor (to prevent an unintended rainout effect).
Each winter we impose an El Nino-like rainfall regime (50% increase over long-term average for non-El Nino years) using an irrigation system and RO water. El Nino rains are added in 6 experimental storm events that mimic actual El Nino winter-storm event size and frequency. During El Nino years we use ambient rainfall and do not impose experimental rainfall events. For N deposition, we add 2.0 g m-2 y-1 of N in the form of NH4NO3 because NH4 and NO3 contribute approximately equally to N deposition at SNWR (57% NH4 and 43% NO3; Bez et al., 2007). The NH4NO3 is dissolved in 12 liters of deionized water, equivalent to a 1 mm rainfall event, and applied with a backpack sprayer prior to the summer monsoon. Control plots receive the same amount of deionized water.
Soil temperature is measured with Campbell Scientific CS107 temperature probes buried at 2 and 8 cm In the soil. Soil volume water content, measured with Campbell Scientific CS616 TDR probes is an integrated measure of soil water availability from 0-15 cm deep in the soil. Soil CO2 is measured with Vaisala GM222 solid state CO2 sensors. For each plot, soil sensors are placed under the canopy of B. eriopoda at three depths: 2, 8, and 16 cm. Measurements are recorded every 15 minutes.
CO2 fluxes are calculated using the CO2, temperature, and moisture data, along with ancillary variables following the methods of Vargas et al (2012) Global Change Biology
Values of CO2 concentration are corrected for temperature and pressure using the ideal gas law according to the manufacturer (Vaisala). We calculate soil respiration using the flux-gradient method (Vargas et al. 2010) based on Fick’s law of diffusion where the diffusivity of CO2 is corrected for temperature and pressure (Jones 1992) and calculated as a function of soil moisture, porosity and texture (Moldrup et al. 1999).
Instrument Name: Solid State Soil CO2 sensor
Model Number: GM222
Instrument Name: Temperature Probe
Manufacturer: Campbell Scientific
Model Number: CS107
Instrument Name: Water Content Reflectometer Probe
Manufacturer: Campbell Scientific
Model Number: CS616
This study explores the population dynamics of black-tail jackrabbits (Lepus californicus) and desert cottontail rabbits (Sylvilagus auduboni) in the grasslands and creosote shrublands of McKenzie Flats, Sevilleta National Wildlife Refuge. The study was initiated in January 1992, and continues quarterly each year. Rabbits are sampled via night-time spotlight transect sampling along the roads of McKenzie Flats once during winter, spring, summer, and fall. The route is 21.5 miles long. Measurements of perpendicular distance of each rabbit from the center of the road are used to estimate densities (number of rabbits per square kilometer) via Program DISTANCE. Results from January 1992 to May 2004 indicated that spring was the period of peak density period, with generally steady declines through the rest of the year until the following spring. Evidence of a long-term "cycle" (e.g., the 11-year-cycle reported for rabbits in the Great Basin Desert) does not appear in the Sevilleta rabbit populations.
The purpose of the study is to assess the dynamics of rabbit populations in the grasslands and creosote shrublands of the Sevilleta NWR. Rabbits are important herbivores in these habitats, and can influence net primary productivity and plant species composition. In turn, these animals also provide high-quality prey for many of the Sevilleta NWR's carnivores and birds of prey. Density data on rabbits can also be used to calculate herbivore pressure on the plant communities.
The rabbits are sampled along 21.5 miles of roadway that is broken up into four "legs" of varying lengths.
Leg A:Black Butte southward to Five Points (5.7 miles).
Leg B:Five Points eastward to the turnoff before Palo Duro Canyon (4.1 miles).
Leg C: Palo Duro turnoff northward to the old McKenzie Headquarters site (6.1 miles).
Leg D: McKenzie Headquarters site northwestward to Black Butte (5.6 miles).
Frequency of Sampling:
Sampled one night per season, four seasons per year.
Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake.1993. Distance Sampling. Estimating abundance of biological populations. Chapman and Hall, New York. 446 pp.
The rabbit surveys are conducted at night using spotlights positioned out each side of a pick-up truck. Surveys began one hour after sunset, when no trace of sunlight or dusk remained. Beginning in 1998, all surveys are conducted on or near the full moon.
The truck is driven slowly (8-10 miles per hour) along the 21.5 mile circuit. Two (or more) observers stand in the bed and scan the left and right sides (respectively) of the road with spotlights, while the driver keeps watch for rabbits directly in front of the vehicle.
During 1992, the spotlights were Q-Beam 500,000 candlepower spotting lights, with both flood and spot settings (spot settings were used during the rabbit sampling). From 1993 through 1996, Q-Beam spotlights with 1,000,000 candlepower were used. In 1997, new spotlights with 3,000,000 candlepower were used; these lights were set permanently on "flood", but illuminated distances previously reached by the spot settings of the less-powerful spotlights. SInce 2002, 2,000,000,000 candlepower spotlight gave been used.
In addition to the spotlights used by the standing observers in the bed of the pickup truck, two spotlights mounted on the pillar posts of the truck's cab are turned on and set for the roadsides ahead of the truck; these lights, coupled with the high-beam setting of the truck's headlights, illuminate the road in front of the truck for approximately 100 meters. When a rabbit is observed, one person's spotlight illuminates the spot at which the rabbit was first seen. The second person's spotlight tracks the rabbit so it is not counted twice. A meter tape is walked out from the center of the truck bed (i.e., the center of the road) perpendicular to the location at which the rabbit was first observed. That distance is measured and recorded to the nearest meter. If a rabbit is observed in the middle of the road, the distance is recorded as zero.
Beginning in Jan. 2000, perpendicular distances are measured using a laser range finder, with an accuracy of 1 meter. Accuracy level is checked prior to sampling. Generally, rabbits within 100 meters of the road can be seen relatively clearly with all three types of spotlights.
Other data recorded includes (1) the odometer reading in miles from the beginning of the sample at Black Butte (odometers are reset to zero at the start of the sample), (2) whether the rabbit was on the left or right side of the road, and (3) the species of rabbit. Incidental data on weather conditions is also noted including presence of clouds and moon, time at which the survey was begun, and times at which each leg was begun and finished. The names of the people on the sampling crew are also recorded.
Perpendicular distance data are entered into Program DISTANCE to estimate the total density of rabbits in the study area. Values are computed as numbers of individuals per square kilometer.
2,000,000,000 candlepower Q-Beam spotlights.
File created 23 Nov. 1992 - SM
1-30-95: 1-23-95 data entered by Rosemary Vigil.9-11-97: doc file created by Robert R. Parmenter 9-11-97: 4-25-95 through 8-4-97 data entered by Robert R. Parmenter 9-19-97: archived by Gregg MacKeigan as rabbit_survey_92-97.dbf. 10-29-97: data for 10-27-97 entered and checked by Robert R. Parmenter 2-6-00: data for 1998, 1999, and Jan. 2000 entered and checked by Robert R. Parmenter. 12-25-00: data for April, July, and October 2000 entered and checked by Robert R. Parmenter. 2-6-01: data for February 2001 entered and checked by Robert R. Parmenter. 2-5-02: data for April, July and October 2001, and January 2002, entered and checked by Robert R. Parmenter. 6-26-02: data for April, 2002, entered and checked by Robert R. Parmenter. 7-24-02: data for July, 2002, entered and checked by Robert R. Parmenter. 10-25-02: data for October, 2002, entered and checked by Robert R. Parmenter. 12-30-05: data for 2003 and 2004 entered and checked, and final edits to metadata file made by Robert R. Parmenter. doc
Dates of collection vary in some years, but sampling is generally conducted in January, April, July, and October.
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