This dataset consists of profiles of soil water potential measured via in situ thermocouple psychrometers located within a rainfall manipulation experiment in a piñon-juniper woodland. The sensors are centrally located within 40 m x 40 m water addition, water removal, infrastructure control, and ambient control plots. The profiles are installed under each of ten target piñon and juniper trees (five of each species) which were also used for other physiological measurements, as well as at five intercanopy areas. The raw sensor output (in μV) has been temperature-corrected and individual calibration equations applied.
Background: This sensor array is part of a larger experiment investigating the mechanisms of drought-related mortality in the piñon-juniper woodland. Briefly, one hypothesis is that, during periods of extended, very-negative, soil water potential (“drought”) trees experience xylem tensions greater than their threshold for cavitation, lose their hydraulic connection to the soil, dessicate and die. A second hypothesis is that in order to avoid this hydraulic failure, trees restrict water loss via reduction in stomatal conductance which also limits the diffusion of CO2 for photosynthesis, and eventually may starve to death depending on the drought duration.
The goal of the project is to apply drought stress on an area significantly larger than the scale of individual trees to determine whether hydraulic failure or carbon starvation is a more likely mechanism for mortality under drought conditions. The cover control treatment replicates the microenvironment created under the plastic rainfall removal troughs (slightly elevated soil and air temperatures and relative humidity) without removing ambient precipitation. The water addition treatment is intended to simulate 150% of the 30-yr average rainfall via n = 6 19-mm super-canopy applications during the growing season (April-October). More details on the experiment can be found in Pangle et al. 2012 Ecosphere 3(4) 28 (http://dx.doi.org/10.1890/ES11-00369.1). These three treatments, in addition to an ambient control with no infrastructure, are applied to three replicated blocks, one on relatively level terrain, one on a southeast-facing slope, and one on a north-facing slope. The soil psychrometers were installed in the southeast-facing block only, to measure the effectiveness of the treatments on plant-available soil moisture.
For the purposes of comparing soil water potential under various cover types (piñon, juniper, intercanopy), it should be noted that significant tree mortality has occurred on Plot 10. As described below, on 5 August 2008 the site was struck by lightening and many of the soil psychrometers were rendered inoperable. At approximately the same time, four of the five target piñon trees in the southeast-facing drought plot (Plot 10) started browning and it was discovered that they had bark beetle (Ips confusus) galleries and were infected with Ophiostoma fungi. By October 2008 those trees (T1, T2, T4, and T5) had dropped all their needles. Therefore the psychrometers buried under them were no longer located “under trees” after that time. By June 2009 the remaining target piñon (T3) died. By March 2010, one of the target juniper trees (T10) had died. At the time of this writing (April 2011) it is anticipated that more of the juniper trees on P10 will die during this year.
Methods: Within Plots 9-12 of the larger PJ rainfall manipulation experiment, thermocouple psychrometers (Wescor Inc., Logan, UT, USA) were installed. Soil psychrometers profiles were placed under each of the initial ten target trees in each plot, and at the same five intercanopy areas that were instrumented to measure soil and air temperature and soil volumetric water at 5 cm depth. Each profile consisted of sensors at (1) 15 cm; (20) cm; and (3) as deep as could be augered and installed by hand, generally 50-100 cm depth. Sensors were calibrated with four NaCl solutions of known water potential before field deployment.
Sensors are controlled via a Campbell Scientific CR-7 datalogger (Campbell Scientific, Logan, UT, USA). The datalogger takes measurements every 3 h but soil water potential does not change that fast and the daytime measurements are generally unusable because of thermal gradients between the datalogger and the sensors, therefore the data presented here are only the 3:00 AM timepoints.
Note that on 5 August 2008 the site was struck by lightening. Many of the soil psychrometers were destroyed by ground current, with the worst damage on the drought and cover control plots where the metal support posts for the infrastructure may have helped to propagate ground current. Some of those sensors were eventually replaced but in the case of the infrastructure plots we were limited to installing new sensors between the plastic troughs because it was impossible to auger under the plastic. Therefore, while the original installation was random with regard to the pattern of plastic domes and troughs, the replacement installation was exclusively outside the plastic and the data may therefore be biased towards wetter microsites.
Instrument Name: thermocouple psychrometer with stainless steel screen
Manufacturer: Wescor, Inc, Logan, UT, USA
Model Number: PST-55
Climate models predict that water limited regions around the world will become drier and warmer in the near future, including southwestern North America. We developed a large-scale experimental system that allows testing of the ecosystem impacts of precipitation changes. Four treatments were applied to 1600 m2 plots (40 m × 40 m), each with three replicates in a piñon pine (Pinus edulis) and juniper (Juniper monosperma) ecosystem. These species have extensive root systems, requiring large-scale manipulation to effectively alter soil water availability. Treatments consisted of: 1) irrigation plots that receive supplemental water additions, 2) drought plots that receive 55% of ambient rainfall, 3) cover-control plots that receive ambient precipitation, but allow determination of treatment infrastructure artifacts, and 4) ambient control plots. Our drought structures effectively reduced soil water potential and volumetric water content compared to the ambient, cover-control, and water addition plots. Drought and cover control plots experienced an average increase in maximum soil and air temperature at ground level of 1-4° C during the growing season compared to ambient plots, and concurrent short-term diurnal increases in maximum air temperature were also observed directly above and below plastic structures. Our drought and irrigation treatments significantly influenced tree predawn water potential, sap-flow, and net photosynthesis, with drought treatment trees exhibiting significant decreases in physiological function compared to ambient and irrigated trees. Supplemental irrigation resulted in a significant increase in both plant water potential and xylem sap-flow compared to trees in the other treatments. This experimental design effectively allows manipulation of plant water stress at the ecosystem scale, permits a wide range of drought conditions, and provides prolonged drought conditions comparable to historical droughts in the past – drought events for which wide-spread mortality in both these species was observed.
Obviously, one of the important areas of interest in this experiment was the effects of elevated (greater-than-average) and decreased (less-than-average) precipitation levels on soil moisture. The volumetric water content of the soil was monitored across all twelve plots, all four treatment types, and all three cover types. The record created through these monitoring activities not only noted the initial “wetting-up” of the soil after a precipitation event but also tracked the “drying-down” of the soil after the event. The water content of the soil and its associated storage capacity could then provide a frame of reference in which changes in the physiological properties of our two target tree species, such as water potential and sapflow rate, could be interpreted.
The study utilized four different experimental treatments applied in three replicate blocks. The four experimental treatments included 1) un-manipulated, ambient control plots, 2) drought plots, 3) supplemental irrigation plots, and 4) cover-control plots that have a similar infrastructure to the drought plots, but remove no precipitation. The three replicated blocks differed in their slope and aspect. One block of four plots was located on south facing slopes, one on north facing slopes, and one in a flat area of the landscape.
Experimental Treatment Design (see Pangle et al. 2012 for detailed methodology)To effectively reduce water availability to trees, we installed treatments of sufficient size to minimize tree water uptake from outside of the plot. Thus, we constructed three replicated drought structures that were 40 m × 40 m (1600 m2). We targeted a 50% reduction in ambient precipitation through water removal troughs that covered ~50% of the land surface area. Drought plot infrastructure was positioned to insure that targeted Piñon pine and juniper were centrally located within each drought plot to provide the maximum distance between tree stems and the nearest plot boundary. Each drought and cover-control plot consists of 27 parallel troughs running across the 40 m plot. Each trough was constructed with overlapping 3ft ×10 ft (0.91 m × 3.05 m) pieces of thermoplastic polymer sheets (Makloron SL Polycarbonate Sheet, Sheffield Plastics Inc, Sheffield, MA) fixed with self-tapping metal screws to horizontal rails that are approximately waist height and are supported by vertical posts every 2.5-3.5 m. The plastic sheets were bent into a concave shape to collect and divert the precipitation off of the plot. The bending and spacing of the plastic resulted in 0.81 m (32 in) troughs separated by 0.56 m (22 in) walkways. Individual troughs often intersected the canopy of trees because of their height. The troughs were installed as close to the bole of the tree as possible without damaging branches in order to maximize the area covered by the plastic across the entire plot. An end-cap was attached to the downstream edge of the trough to prevent water from falling onto the base of the tree. A piece of 3 in (7.62 cm) PVC pipe or suction hose (used when the bole of a tree was directly below trough) was then attached to the downstream side of the end-cap, enabling water to flow into the trough on the other side of a tree. End-caps were also placed at the downhill end of the troughs on the edge of the plot and fitted with 90 degree fittings to divert water down into a 30 cm2 gutter (open on top) that ran perpendicular to the plot. Collected water was then channeled from the gutter into adjacent arroyos for drainage away from the study area. We built cover-control infrastructures to investigate the impact of the plastic drought structures independent of changes in precipitation. This was necessary because of the high radiation environment in central New Mexico, in which the clear plastic troughs can effectively act as a greenhouse structure. The cover-control treatment had the same dimensions as the drought plots with one key difference. The plastic was attached to the rails in a convex orientation so precipitation would fall on top of the plastic and then drain directly down onto the plot. The cover-control plots were designed to receive the same amount of precipitation as un-manipulated ambient plots, with the precipitation falling and draining into the walkways between the rows of troughs. Cover-control plots were constructed between June-21-07 and July-24-07; drought plots were constructed between August-09-07 and August-27-07. The total plastic coverage in each plot is 45% ± 1% of the 1600 m2 plot area due to the variable terrain and canopy cover. Our irrigation system consisted of above-canopy sprinkler nozzles configured to deliver supplemental rainstorm event(s) at a rate of 19 mm hr-1. Our irrigation system is a modified design of the above-canopy irrigation system outlined by Munster et al. (2006). Each of the three irrigation plots has three 2750 gal (10.41 m3) water storage tanks connected in parallel. These tanks were filled with filtered reverse osmosis (RO) water brought to the site with multiple tractor-trailer trucks. During irrigation events, water is pumped from the tanks through a series of hoses attached to 16 equally-spaced sprinklers within the plot. Each sprinkler is 6.1 m (20 ft) tall (2-3 m higher than mean tree height), and fitted with a sprinkler nozzle that creates an even circular distribution of water with a radius of 5 m on the ground. The irrigation systems were tested in October 2007 (2 mm supplemental), and full applications (19 mm) were applied in 2008 on 24-June, 15-July, and 26-August. During subsequent years (2009-2012), a total of four to six irrigation events (19mm each) were applied (please contact Will Pockman and/or Robert Pangle for specific application dates and rates).
Site Abiotic Monitoring
Site Abiotic Monitoring (please see Pangle et al. 2012 for more detailed methodology) We used Campbell Scientific dataloggers to continuously monitor and record abiotic conditions and physiological measurements across the site. All systems were connected to a solar-powered wireless network with NL100 relays (Campbell Scientific, Logan, UT). Plots were instrumented with CR-1000, CR-7, and CR-10X dataloggers (Campbell Scientific, Logan, UT). Each CR-1000 datalogger was accompanied by AM25T and AM 16/32 multiplexers to expand sensor measurement capacity (Campbell Scientific, Logan, UT). Abiotic conditions were measured under each cover type (n=3-5 locations per cover type): under piñon, juniper, and intercanopy areas between trees. These measurements included; a) soil temperature (TS) at –5 cm depth and shielded air temperature (TA) at 10 cm (above soil surface), both measured with 24 gauge Type–T thermocouples (Omega, Stamford, CT), b) shallow soil volumetric water content (VWC) at –5 cm measured using EC-20 ECH2O probes (Decagon, Pullman, WA), and c) soil VWC at depth using EC-5 soil moisture probes (Decagon, Pullman, WA). Soil VWC profiles had sensors installed at –15 cm, –20 cm, and as deep as possible (down to –100 cm, depending on soil conditions).
Data processing and QA-QC were performed using either Matlab (The Mathworks, Inc.) or Microsoft Office 2010 Excel (Microsoft Corporation) software. All raw and/or processed data traces were visually plotted and inspected for noisy, erroneous, or out of range data points or sensors traces. All removed data points had a “NaN” value assigned. Despite this QA-QC review and data cleaning, all data sets should still be evaluated for outliers, etc., as standard outlier statistical tests were not performed.
The VWC_5cm depth data-set contains 15 minute interval data from 2006 thru 2012. Data Qa/Qc has been performed on these files. PJ day refers to days since start of project (i.e., 1/1/2006). PJ Timestamp denotes/records each 15 minute interval entry from 1/1/2006.
The treatment classes provided in the file are as follows; ambient control (1), drought (2), cover control (3), and irrigation (4). The experiment used plot aspect as the blocking factor. There are 3 different replicate blocks and block classifications designated in the files; flat aspect (1), north aspect (2), and south aspect (3). This will be obvious when viewing the files.
Values are reported in decimal % (in other words, a 0.25 data entry = 25%). There are three cover types within each plot; 1) VWC (5cm) data under Piñon canopy cover, 2) VWC (5cm) under juniper canopy cover, and 3) VWC (5cm) at inter-canopy locations (i.e., bare, no canopy cover). The VWC (5cm) data was collected from probes installed/buried at 5cm soil depth.
Detailed information on VWC-5cm header columns for the Tree_Number, SensorID, Species, and Sensor_Location variables. Tree_Number refers to the label given to each sensor probe (i.e., it is installed beneath a specific target tree or a bare inter-canopy location). The SensorID is an identifier that provides both the Tree_Number information and the soil depth of the probe. Species indicates the cover type where the measurement was made; PIED, JUMO, or bare ground/intercanopy (INCA). And the Sensor_Location simply indicates the depth where the soil moisture (VWC) probe is installed.
Tree numbers are always grouped by species as follows (regardless of plot); Trees 1-5 are original Pinus edulis, Trees 6-10 are original Juniper monosperma. B1 through B5 always designate an inter-canopy (i.e., bare) location. Note, for the VWC_5cm data – there are no or very few “replacement” trees. All (or most all) VWC_5cm measurements were made original target trees, i,e., the sensor installation positions/locations remained in their original locations regardless of any later tree death or mortality.
Similar to the Sapflow-JS data, there may be differing tree labels (and sample sizes, i.e., n=3, n=4, or n=5) for each cover type in differing plots depending on; 1) the specific target trees under which measurements were made, and 2) the total number of target trees in a given plot under which soil moisture probes were installed (this varies from n=3 to n=5 per cover type for differing plots). This will be obvious when you view the files for different plots.
The goal of this project is to determine the nature and magnitude of changes in the hydrologic properties of arid soils with increasing amounts of pedogenic calcium carbonate. The amount and morphology of the calcium carbonate in arid soils varies laterally and vertically with changes in the age of the soils, thus the hydrologic properties also vary systematically The calcium carbonate cements soil particles changing the apparent texture of the soil horizon and thus other soil properties such as structure, porosity, moisture retention, and unsaturated and saturated hydraulic conductivity also change significantly. There has been no systematic study of the impact of increasing amounts of calcium carbonate on the hydrologic properties of semi-arid soils. The ultimate goal of this study is to provide a basis for developing more accurate pedotransfer functions, which are the main methods for obtaining soil hydrologic properties of rangeland soils.
Selection of Surfaces: Three terraces of different ages were chosen at the outlet of a small watershed basin at the base of Sierra Ladrones in North West Sevilleta National Wildlife Refuge. These surfaces have shown varying stages of calcic horizons.
Digging Pits: 3 Pits up to a meter deep were dug on each surface.
Describing the Soils: the soil profile in each pit was described using USDA soil survey guidelines.
Soil Sampling: From every pit, soil samples were collected every 10 cm. Also soil peds were collected from every horizon for bulk density analysis.
Infiltration Experiment: In order to check the soil hydraulic conductivity, a tension disk infiltrometer was used on every soil horizon in each pit.
Laboratory Analysis: The soil samples were split and sieved for laboratory analysis
CaCO3 Content: The total inorganic carbonate content was calculated using Chittick’s apparatus
Bulk Density: The bulk density of the soil peds was calculated using the Clod’s apparatus.
PSDA: Particle size distribution analysis was carried out with the presence of carbonate on the 2mm sample.
Carbonate Digestion: The carbonate was digested to remove the amount of carbonate from the sample. PSDA was performed again on the soil samples without the carbonate.
Information on Collection Sites:
Study Area 1:
Study Area Name: Surface 1(Pit 1)(Young Surface)
Study Area Location: Outlet of the small watershed basin at the base of Sierra Ladrones
Study Area Description:
Elevation: 1623 m
Geology: Quaternary Sierra Ladrones Formation
Soils: Laborcita-Pilabo-Lemitar complex
Climate: Semi arid, Rainfall ~ 250 mm
North Coordinate: 34° 24.5’
West Coordinate: 106° 58.1'
Study Area 2:
Study Area Name: Surface 2 (Pit 2)(Intermediate Surface)
Elevation: 1615 m
Geology: Quaternary Sierra Ladrones Formation
Climate: Semi-arid, Rainfall ~250 mm
North Coordinate: 34° 24.491'
West Coordinate: 106° 58.046'
Study Area 3:
Study Area Name: Surface 3 (Pit 3) (Oldest Surface)
Elevation: 1633 m
Climate: Semi-arid, Rainfall~250 mm
North Coordinate: 34° 24.405'
West Coordinate: 106° 58.020'
Other Field Crew Members: Ritchie Andre and Ramirez Carlos
Fire resulting from natural ignition has become a more common event on the Sevilleta National Wildlife Refuge (NWR) since the exclusion of domesticated livestock. Efforts to return fire to the native landscape has resulted in the use of prescribed fire during periods that meet burn prescriptions. A prescribed fire was performed on the Sevilleta NWR in June 2003. Among the measured site and burn characteristics that were measure, this project sampled soils before and after the fire from 5 previously-sampled locations that were burned in June 2003 and from 5 newly established locations that served as controls. The controls were within an area that was sampled between 1989 and 1996 for similar properties measured in this study and had previously been tested to be similar to the locations burned in 2003. The soil properties that are repeatedly measured at the burn and control locations include: field water content; water-holding capacity; organic matter; field extractable nitrate and ammonium; and potentially mineralizable nitrogen.
The removable bridge is placed upon the end rebar and the middle pin is secured in the depression on the nail beneath the middle hole (#16). The bridge is then leveled and individual pins are inserted to the soil surface. If the surface is firm enough, the pins are left unsecured. If the surface is too soft, the pins are secured with the tip at the soil surface by attaching a clothspin above the bridge. The heights of each pin above the bridge are recorded, and cover is recorded if the pin struck vegetation when being inserted and basal cover is recorded if the pin rested upon the basal portion of a plant at the ground surface. The standard soil bridge developed for the Sevilleta was used. The bridge contains 31 holes at 5 cm intervals with the middle hole used to orientate the bridge above a nail left at the ground surface, and which provides a reference to secure the line and the bridge height. Also referenced at (http://sevilleta.unm.edu/data/contents/SEV065/).
For inorganic N extractions and potentially mineralizable N measurements, a soil core of 4-cm diameter was taken to 20-cm depth beneath two nearby grass clumps (the two cores were compostited; termed under) and from two bare soil patches (two cores were composited; termed open) within 5 m of the stake identifying each bridge or from the bridge stake with the identification tag (new control bridges). All soil samples were placed into an ice chest and transported on ice directly to the University of New Mexico UNM, where they were sieved (< 2 mm), mixed, and stored at 5 degrees C. All soil N measurements were performed at UNM.
After determining fresh water content and water-holding capacity (WHC)(White and McDonnell 1988), fresh portions of each sample were adjusted to 50% of determined WHC and subsamples of 20 g dry-weight were apportioned into plastic cups. One subsample of each sample was immediately extracted with 100-ml 2 N KCl for NH4+-N and NO3-N analyses to determine field-available N. Two additional cups were covered with plastic wrap, sealed with a rubber band, and incubated in the dark at 20 degrees C. The plastic wrap minimized water loss during incubation, yet exchange of CO2 and O2 was sufficient to keep the subsamples aerobic during incubation. Moisture content was monitored by mass loss and replenished as needed. After contact and settling for 18-24 h, the clarified KCl was filtered through a Kimwipe and analyzed for NH4+-N and NO3--N+NO2--N on a Technicon AutoAnalyzer (Technicon, Terrytown, NY) as described in White (1986). After incubation for 6 weeks, a subsample of each soil was extracted with KCl and analyzed for NH4+-N and NO3--N+NO2--N. Potentially mineralizable N was determined to be the amount of extractable N in the 6-week extraction.
Organic matter was determined by loss-upon-ignition in tin cups following heating at 500C for two hours.
Soil Physical/Chemical Properties
Soil cores were taken beneath grass clumps in which the temperature pellets were placed both before and after the fire. At least 300 g of soil were taken to a depth of 10 cm (NOTE:different depth than nitrogen cycling)
Fire temperature was determined with pellets supplied by Tempil (2901 Hamilton Blvd., South Plainfield, NJ 07080; www.tempil.com). A set of 15 foil-wrapped tablets, with melting temperatures ranging from 85 C to 1533 C, were strungon wire and suspended about 1 inch above the ground. The fire temperature was assumed to be greater than the temperature at which the corresponding pellet showed signs of melting and less than the temperature of the next highest undamaged pellet. The pellets were suspended within two clumps of dominant grasses at the site (black grama).
Pre-existing briges (1.1 through 1.5) were selected to be included within a prescribed burn area. Data collected from the bridges were consistent with existing data collection: (http//sevilleta.unm.edu/data/contents/SEV065/ ) and included soil surface elevation, plant aboveground cover and basal cover. Soils from beneath a nearby grass clump and from bare interspaces were collected for analysis of soil properties. Soil temperature pellets were placed within grass clumps from beneath which soils were collected. Pre-fire on control and expected burn plots, and post-fire on burn plots only for soil elevation, aboveground plant cover and basal cover, N mineralization potentials, field moisture, water holding capacity, and loss upon ignition for organic matter. Pre and post burn soil samples were collected beneath grass clumps at the existing bridges for analysis of soil properties (sent ot Jane Belnap). Fire temperature was measured with temperature tablets placed about 1 cm above the ground within the grass clump that was sampled for soil properties and in an adjacent grass clump of similar appearance.
Changes to the data: Data were updated to include 2007 data on 5/15/2008 by Carl White.
Additional Study Area Information
Study Area Name: Bridge 1.1
Study Area Location: north end of five bridges; black grama dominated grassland; MacKensie Flats; Site is 5 m area around bridge; Bridges setup in 1994 to monitor changes in soil surface elevations to understand the dynamics of soil particles and associatednutrients. North Coordinate: 34.3358 South Coordinate: 34.3358 East Coordinate: -106.6954 West Coordinate: -106.6954
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