This study measured 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 begun in January, 1992, and continued quarterly each year. Rabbits were sampled via night-time spotlight transect sampling along the roads of McKenzie Flats during winter, spring, summer, and fall of each year. The entire road transect was 21.5 miles in length. Measurements of perpendicular distance of each rabbit from the center of the road were used to estimate densities (number of rabbits per square kilometer) via Program DISTANCE. Results from 1992 to 2002 indicated that spring was the peak density period of the year, with generally steady declines through 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) did not appear in the Sevilleta rabbit populations.
The purpose of the study was 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 NPP and plant species composition. In turn, these animals also provide high-quality prey for many of the Sevilleta's mammal and reptile carnivores and birds of prey. Density data on rabbits can be used to calculate herbivore pressure on the plant communities.
When the samples were collected: The samples were collected in winter, spring, summer, and fall, of each year. Rabbit populations were sampled during a single night during each of these four seasons per year. Dates of collection varied in some years, but generally the sampling was conducted in January, April, July, and October.
Sampling Design: The rabbits were sampled along 21.5 miles of roadway that was 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).
Measurement Techniques: The rabbit surveys were conducted at night using spotlights. Surveys began one hour after sunset, when no trace of sunlight or dusk remained. Beginning in 1998, samples were taken only during full-moon periods. A pickup truck was driven slowly (8-10 miles per hour) along the road of the 21.5 mile circuit. Two (or more) observers stood in the bed of the pickup truck, and scanned the left and right sides (respectively) of the road with spotlights, while the driver kept watch for rabbits directly in front in the road. 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 well at distances previously reached by the spot settings of the less-powerful spotlights.
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 were turned on and set for the roadsides ahead of the truck; these lights, coupled with the high-beam setting of the truck's headlights, illuminated the road in front of the truck for approximately 100 meters. When a rabbit was observed, one person's spotlight illuminated the spot at which the rabbit was first seen. The second person's spotlight would track the rabbit, so that it was not counted twice. A meter tape was walked out from the center of the truck bed (which equalled the center of the road) in a perpendicular direction from the road to the location at which the rabbit was first observed. That distance was measured and recorded to the nearest meter.
If a rabbit was observed in the middle of the road, the distance was recorded as zero. Beginning in January, 2000, perpendicular distances to the rabbits were taken with a laser range finder, with accuracies of less than 1 meter (accuracies were tested before field use and confirmed to be <1m). Generally, rabbits within 100 meters of the road could be seen relatively clearly with all three types of spotlights. Other data recorded included (1) the odometer reading in miles from the beginning of the sample at Black Butte (odometers were 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. In addition, incidental data were recorded on weather conditions, presence of clouds and moon, and the time at which the survey was begun, along with the times at which each Leg was begun and finished. Finally, the names of the people on the sampling crew were recorded.
Analytical Procedures: The perpendicular distance data were entered into Program DISTANCE to estimate the total density of rabbits in the study area. Values were computed as numbers of individuals per square kilometer In the analyses, if there were sufficient numbers of rabbits (>10 per leg), the difference legs were analyzed separately, and the resulting mean densities were estimated by averaging the four leg estimates. In the results tables below, these instances are indicated by the category, "MEAN". If sample sizes were too small to estimate the four legs separately, then all the rabbit observations were pooled together, and a density estimate for the entire 21.5 mile survey was calculated. These results are indicated by the category, "ALL".
The program DISTANCE command codes were as follows:
Stratum/label='DATE ENTERED HERE';
LEGS, DATE ENTERED HERE'/Effort=21.5;
DISTANCE DATA ENTERED HERE, SEPARATED BY COMMAS;
Est /key=uniform /adj=cosine /select=sequential /criterion=AIC /monotone=weak;
Est /key=uniform /adj=hermite /select=sequential /criterion=AIC /monotone=weak;
Est /key=hnormal /adj=cosine /select=sequential /criterion=AIC /monotone=weak;
Est /key=hnormal /adj=hermite /select=sequential /criterion=AIC /monotone=weak;
Density by sample;
Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta NWR in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of what is now the SNWR during the 1960’s, prior to their systematic eradication. In 2010, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a site that was occupied by prairie dogs 40 years ago. This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem. With this project, we would like to further investigate the impact that Gunnison’s prairie dogs have on the landscape. Gunnison’s prairie dog monitoring data has been collected from the beginning of the reintroduction project, but little information has been collected on how grassland species respond to the sudden presence of prairie dogs on the refuge.
This project will help determine if the prairie dog reintroduction has had positive impacts on the grassland ecosystem. Prairie dogs benefit grasslands in many ways, but their role as ecosystem engineers directly impacts other species by creating new habitat that would not be present without prairie dogs. We have documented physical landscape changes, but we have not specifically documented benefits to other grassland species. This work will help determine if the reintroduced prairie dog populations on Sevilleta NWR are now acting as a keystone species in a grassland ecosystem by monitoring small mammal populations to see if species richness, diversity, and density are different on prairie dog colonized areas versus non-colonized areas.
Trapping Location and Design:
Trapping will be done on the 16ha Prairie Dog Relocation Study Plots. There are 4 of them- A, B, C, and D. Each plot will have 169 traps placed in a grid covering 9 hectares. Using the vegetation quad map, there will be a trap placed at 1 meter to the north at each of the following vegetation plots 11-17, 20-26, 29-35, 38-44, 47-53, 56-62, 65-71. This accounts for 49 of the traps. There will also be a trap placed in between each veg plot, with rows running North/South, which accounts for 42 more of the traps. Then making a complete row in between the North/South vegetation quad rows, will account for the remaining 78 traps. To locate the veg plots, each are marked with a rebar and short white PVC. There is a numbered tag on each PVC corresponding to the map.
Flag each trap with a numbered pin flag to designate trap numbers. This is important in ensuring that all traps are checked and closed each day.
Trapping period will be one plot a week for 4 nights.
The traps are set each evening for four nights. This entails setting and baiting the traps at a given locality on Monday afternoon, then checking the traps at dawn on Tuesday (night 1), Wednesday (night 2), Thursday (night 3), and Friday (night 4). Each trap is baited with a handful of steamed, crimped oats tossed into the trap after it is placed on the ground; a few oats are left outside the trap entrance to entice passers-by. The ground needs to be smoothed out with a foot to make sure that the trap is level and not unbalanced.
Each morning, traps are checked as follows: the worker walks up and down the transects and closes open traps as you go along. Traps are not reopened until the late afternoon/early evening, at which time additional bait is also put in. When a closed trap is encountered, it is first checked to see if an animal is present by carefully and just slightly opening the door of the trap and looking inside. Be aware that kangaroo rats can jump out while doing this, so use caution. Sometimes, although a trap may appear empty, a tiny rodent may be hiding under the treadle (especially in the large traps). To check for this, one must reach into the trap and lightly push down the treadle. If the treadle will not go down, there is likely a mouse underneath. If no animal is in the trap, the trap is left closed until the afternoon. If a trap has an animal, the worker processes the animal at the stake and takes the relevant data. While checking for animals on Friday morning (night four), traps are picked up, emptied of seed, and returned to storage boxes, ready for placement at another locality the following week. Importantly, traps MUST BE counted as they are placed into storage boxes in order to insure that no traps (or animals) are left on the plot. If rain falls on the baited traps, they may require cleaning and drying back at the field station before storage or use the following week.
Removing rodents from trap
For each capture, the trap number is recorded first. Next, a given animal is shaken from the trap into a plastic gallon ziploc bag. This is accomplished by wrapping the opening of the ziploc bag over the door end of the trap. Make sure that they bag is tight so the rodent can’t squeeze out between the bag and the trap. Open the front door through the bag and lock open. Roll the trap upside down and swing it in an arc downward. As soon at the rodent enters the bag, close the bag off with your hand so the rodent cannot reenter the trap. With kangaroo rats, you often do not need to shake the trap to get the animals out. Instead, put the Ziploc bag on trap as normal and open trap door, but hold the trap angled upward instead of down and the rodent should come out on its own. Hold tight on the bag though because sometimes they come out rather quickly.
If a trap is triggered, but appears empty, don’t assume there is no animal in trap. Small species such as pocket mice can hide under the treadle. Make sure and lightly press down on the treadle to make sure it goes all of the way down. If not then there is most likely a rodent under treadle. You can also open up the back door to look under treadle, but use caution as to not let rodent escape.
If another animal (lizard, bird, rabbit, prairie dog) is caught in the trap, they can simply be released. However, make sure and mark on data sheet that the trap was closed due to bird/lizard/rabbit. If you do find a trap that was triggered by wind or large animal and is in fact empty, make sure and mark on the datasheet that that trap number was triggered but empty.
Handling and Processing rodents
In the bag, the processor positions the rodent with its head in the corner of the bag. Hold its head down with one hand from the outside of the bag, pressing gently on the back of the skull. Then reach in the bag with the other hand and grasp the animal with the thumb and forefingers by the loose skin around the back of the neck and shoulders, and then remove it for inspection.
First off check to see if the rodent is tagged or marked. If it is then you will mark that individual as a recapture on data sheet. After recording the ear tag number or other marking and the species of animal, it can be released. If it is not marked, then it will need to be marked and processed.
Dipodomys spp, Onychomys spp, Neotoma spp, Peromyscus spp, and any other large species you may catch will be uniquely marked with one ear tag. Ear tags should be placed at the very base of the ear on its interior edge (or the front of the ear). Putting it on the external side or back of the ear allows the rodent to rip the ear tag off more easily, by scratching at it with its hind legs.
Other species such as, Perognathus spp, Spermophilus spp, and other small rodents that have too small of ears to place an ear tag, will be marked with sequential individual numbers on their chest, using permanent markers. A different color must be used for each night (blue for 1st night, black for 2nd night, and red for 3rd night). Small rodents do not need to be marked the 4th night, but large rodents do need to be ear tagged. Start with number 1 and increase as necessary for catches.
Next, each animal is identified to species, sexed, and aged. Specific measurements are taken only for those genera which required them for species identification:
Peromyscus: Total length, tail, foot, ear;
Onychomys: Total length, tail, foot.
Perognathus, and Reithrodontomys: Total length, tail.
All measurements are taken to the nearest millimeter using a plastic ruler. The species is recorded by a 4-letter code that represents the first 2 letters of the genus and the first 2 letters of the species.
Sex and reproductive status is then determined by examination of the genitalia (lactating/vaginal/pregnant/scrotal). Look for enlarged scrotum, enlarged nipples, or an enlarged vaginal opening. If none of these are apparent, then the rodent is non-reproductive. Females will still have visible nipples when non-reproductive.
ADULT MALES reproductive status:
-Scrotal (ST): the scrotum can be fully enlarged or partially enlarged.
- Non-reproductive (N)
ADULT FEMALES reproductive status:
-Vaginal (V): in estrus; vagina is obviously swollen and looks large and puckered, vaginal plug can be present or absent
-Pregnant (P): heavier weight, can palpate babies
-Lactating (L): nipples (at least one) reddish and/or enlarged
Before releasing the individual, it is then weighed to the nearest gram, using a Pesola scale clipped to the base of the animal’s tail. Larger animals can easily get off of scale so it is easier to put them back in the bag and weigh them inside the bag. Make sure and weigh bag after rodent is released and subtract from first weight to get actual weight of rodent.
Animals which perished during captivity on plots are noted in the comments on field data sheets as 'D.I.T' (Dead In Trap).
This data is collected each summer, starting in 2013, by an student in the Sevilleta LTER Research Experience for Undergraduates Summer Program. Ear tagging started taking place in the summer of 2014.
Data Collector History
Ty Werdel 2013
Betsy Black & Andrew Velselka 2014
Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta NWR in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of what is now the SNWR during the 1960’s, prior to their systematic eradication. In 2010, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a site that was occupied by prairie dogs 40 years ago. This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem.
Four replicate paired 16 ha plots were established in spring 2010. Each pair consists of a treatment plot with prairie dogs (reintroduced), which are plots B and D and a control plot with no prairie dogs (plots A and C). The closest distance between adjacent plots, either within a block or between blocks, is 200 m (Figure 1). The treatment and control within each pair were randomly assigned. Each plot is a 400x400 m on 9x9 grid array with systematically located sample locations for 81 vegetation quadrats. There are also 4 more plots, E and H are control plots and F and G are treatment plots. F and G have been equipped with artificial burrows and are release sites. However, E and H were not set up to do vegetation quads.
Prairie dogs will be sampled using capture-recapture methods in the summer (3rd week of June) each year and spring (last week of March) and fall when possible.
Set 150 traps within each 300m x 300m trapping area. Place traps in pairs near active burrows at least 4 days prior to trapping. At this time trap doors should be wired open (make certain all traps are properly wired open) with bait trailing from the outside into the back of (or through) the trap. Traps should be baited with sweet feed. Make sure that all traps are functioning properly by testing the trap door sensitivity and adjusting with pliers if needed. Pre-bait traps every morning for 3 days total. All pairs of traps should be numbered with one pin flag for each pair (1-75). All trap pairs should also be GPSed by their number and have maps made for ease of locating traps during trapping.
On the morning of the first trapping day, well before sunrise, the wire should be removed from the traps and the traps then set and baited to capture animals. This can also be done the day before trapping begins. Prairie dogs should be trapped for 3 consecutive mornings.Each morning of trapping, make sure that the traps are all opened well before sunrise, so animals are not disturbed by human activity. This is very important. Traps should only be left opened during the early morning period, until about 10:00 or 11:00 am, depending on the weather conditions and time of year. Prairie dog activity declines by 10:00-11:00, so even if the weather conditions are fine for continued trapping, trap success after this time will decline. Traps should be collected by around 9:00 am, depending on the weather conditions and time of year, and all trapped animals should be brought to a common processing station. The team walks the plot to make sure and check every trap for dogs. As dogs are found trapped, a piece of masking tape is attached to the front of the trap, labeled with the trap number so that that animal can be released where it was trapped. Animals at the processing site should be kept at all times in the shade and carrots should be given to provide moisture during the heat and stress. Once animals have been processed they should be released into their burrow, at the location of their capture. All traps should then be closed for the day. To make sure all are closed, one person should close all the traps from one of the plots and mark the number on the GPS sheet to note the trap has been closed. This can also be done as a team effort, but traps need to be checked twice to make sure they are all closed.
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
Environmental temperature influences virtually all aspects of organismal performance, including fitness. And since temperature varies throughout space and time, organisms must regularly compete for optimal thermal habitats, much as they do for other resources (e.g. territory, food, or females). However, competition for thermal resources imposes costs, often in the form of a stress response (i.e. increased corticosterone production). Elevated corticosterone promotes physiological and behavioral responses that can increase an organism’s chance of survival, but if left in an organism’s system for too long, it will reduce immunity, degenerate neurons, and lower fitness. Previous theoretical and empirical work indicates that, all else being equal, patchy thermal landscapes reduce the energetic cost of thermoregulation. Therefore, I hypothesize that lizards exposed to patchy distributions of preferred temperatures will have less stress (and thus lower levels of corticosterone) than those exposed to clumped distributions. Furthermore, patchily distributed resources are more difficult for territorial males to monopolize, and thus, subordinate males in patchy thermal landscapes should experience less stress than subordinate males in clumped thermal landscapes.
Experimental design: Starting in the July of 2012, I will initiate this project as part of a continuing large-scale field study at Sevilleta LTER site in collaboration with PI Michael Angilletta’s Spatially Explicit Theory of Thermoregulation project. As in past research conducted in 2008, 2009 and 2011, I will use male Yarrow’s spiny lizard. This lizard thermoregulates accurately in the absence of predators14,15 and aggressively defends resources from conspecific males14,16.
Nine outdoor arenas (20 x 20 m), consisting of sheet metal walls and a canopy of shade cloth, will be used to manipulate the thermal environments. Among the arenas, three patterns of shade patches will be replicated three times each to generate distinct thermal landscapes (see Figure 1). Lizards will be paired by size: large dominant (22-30 g) with a small subordinate (15-21 g). Each pair (n = 12) will be randomly assigned one of the thermal environments. Prior to each trial, males will be habituated to their arenas for 10 days. During this period, each male will be exposed to the thermal arena every other day (for a 24-h period) in the absence of a competitor (total of 5 days per animal). After the habituation period, males will be placed in arenas for a 4-day testing period. Males will spend two of these days in isolation and the other two in competition. Half the pairs will start the trial in isolation (solitary treatment), and the other half of the pairs will start the trial in competition (social treatment). A matched pair of lizards will be placed together in one arena, and the other two arenas will each have one individual (either small or large) placed into it. After two days, all lizards will be captured and blood samples will be collected within three minutes (speed of collection is necessary to prevent handling stress from affecting plasma corticosterone levels17). Blood will be taken from the orbital sinus with a glass capillary tube and then taken back to the lab where the plasma will be obtained through centrifugation. Plasma will be stored at -80˚C for hormone assays18. After bleeding, solitary lizards will be placed together in one arena, and the previously paired individuals will be separated and split between the two remaining arenas. Thus, a completed habituation and observation set for six pairs (two pairs per type of thermal environment) will take 14 days. And 3 sets will be conducted per season giving a total of 18 pairs per season in each thermal environment (54 pairs in isolation and competition per season). Mixed modeling procedures in the statistical software R will be used to quantify the effects of competition and thermal patchiness on the corticosterone levels of lizards19.
Fig. 1. Patterns of shade patches for arenas (each replicated 3x).
Biological soil crusts (BSCs) are complex assemblages of fungi, lichens, bacteria, mosses and green algae that stabilize surface soils and manage and traffic photosynthate, nutrients and water to diverse microbial and producer communities in arid environments worldwide. In Sevilleta grasslands, BSCs occupy much of the open space between clumps of vegetation and vary substantially in terms of structure.
BSCs have important biological and physical roles. They have been termed ‘mantles of fertility’ because of their general importance in biogeochemical cycling and net primary production in arid ecosystems. It has been proposed that BSCs play a role in the rapid movement of N, C and water from open areas to plants (see below). BSCs stabilize soils, and physical and chemical disturbances of BSCs lead to topsoil loss and dust storms. BSCs are therefore critical components in efforts to understand implications of both climate change and physical disturbance. Related to this, it has been suggested that BSC diversity can be used to inform conservation policies.
BSCs have been the subject of several previous Sevilleta LTER studies. Green et al. showed that stable-isotope carbon and nitrogen could be transferred bi-directionally between BSCs and adjacent plants. This led Collins et al. to propose that fungal hyphae provide connections between plant roots and BSCs that allow for transport between the two, a proposal known as the “fungal loop hypothesis.” Porras-Alfaro et al. have surveyed the diversity of fungi in BSCs from Sevilleta grasslands using molecular methods. We have also shown that thermophilic fungi are common in BSCs (unpublished results), a result that is not unexpected given the high summer temperatures attained in Sevilleta surface soils. Yet, many questions remain regarding the organisms present in BSCs, their biological roles and how long it takes for BSCs to re-establish after disturbance. Long-term, we are interested in the types of fungi present in BSCs and in how fungi function in transporting nutrients between BSCs and adjacent plants. We are also interested in the extent to which specific fungi provide structure to BSCs and in how they help protect from stress agents such as desiccation. We are interested in the extent to which fungi might help BSCs tolerate high summer soil temperatures, which often reach ≥ 60C. We therefore have a special interest in thermophilic fungi present in the BSCs. To date, little has been done to actually culture fungi from Sevilleta BSCs, hence the need for the current study.
In summary, BSCs are one of the most important features of aridland ecosystems and form a critical interface between physical and biological domains. Understanding the roles of BSCs in protecting soil structure, and in the cycling of carbon, water and nitrogen, is fundamental to aridland ecology. The work proposed here continues efforts to characterize the specific fungi associated with Sevilleta BSCs. It is a modest but important step toward addressing the long-term goals mentioned above.
For each sampling site and sampling period a small amount of surface crust (approx. one teaspoon per sample) was taken from each of 10 locations at approximately 1 meter intervals across a transect. Samples were transported back to the laboratory in plastic bags.
On rare occasions, a larger sample of 0.5 liter volume or less may have been removed at one or two sampling stations.
Data was collected at: LTER PJ site (N 34 23’ 08.7” W 106 31’ 27.0”), a sand dune above the railroad tracks near the Sevilleta wetlands (N34 18' 06.5" W106 51' 14.1"), gypsum outcroppings (N34 12' 40.5" W106 45' 35.5"), grasslands near the Sev LTER warming and monsoon sites (N34 21' 34.3" W106 41' 29.4" and N34 20' 38.1" W106 43' 34.5"), and the Rio Grande Bosque (N34 19'45" W106 51'40").
The distribution, structure and function of mesic savanna grasslands are strongly driven by fire regimes, grazing by large herbivores, and their interactions. This research addresses a general question about our understanding of savanna grasslands globally: Is our knowledge of fire and grazing sufficiently general to enable us to make accurate predictions of how these ecosystems will respond to changes in these drivers over time? Some evidence suggests that fire and grazing influence savanna grassland structure and function differently in South Africa (SA) compared to North America (NA). These differences have been attributed to the contingent factors of greater biome age, longer evolutionary history with fire and grazing, reduced soil fertility, and greater diversity of plants and large herbivores in SA. An alternative hypothesis is that differences in methods and approaches used to study these systems have led to differing perspectives on the role of these drivers. If the impacts of shared ecosystem drivers truly differ between NA and SA, this calls into question the generality of our understanding of these ecosystems and our ability to forecast how changes in key drivers will affect savanna grasslands globally. Since 2006, an explicitly comparative research program has been conducted to determine the degree of convergence in ecosystem (productivity, N and C cycling) and plant community (composition, diversity, dynamics) responses to fire and grazing in SA and NA.
Thus far, initial support has been found for convergence at the ecosystem level and divergence at the community level in response to alterations in both fire regimes and grazing. However, there have also been two unexpected findings (1) the ways in which fire and grazing interact differed between NA and SA, and (2) the rate of change in communities when grazers were removed was much greater in NA than in SA. These unexpected findings raise a number of important new questions: (Q1) Will exclusion of grazing eventually affect community structure and composition across all fire regimes in SA? (Q2) Will these effects differ from those observed in NA? (Q3) What are the determinants of the different rates of community change? (Q4) How will these determinants influence future trajectories of change? (Q5) Will the different rates and trajectories of community change be mirrored by responses in ecosystem function over time? This project is based on a large herbivore exclusion study established within the context of long-term (25-50+ yr) experimental manipulations of fire frequency at the Konza Prairie Biological Station (KPBS) in NA and the Kruger National Park (KNP) in SA. The suite of core studies and measurements include plant community composition, ANPP, and herbivore abundance and distribution at both study sites to answer these research questions.
We used comparable experimental designs and sampling procedures at both URF and KPBS. At URF we used three replicate plots (not hayed or mowed) that have been burned every 1 and 3 years in the spring, and those left unburned (N=9 plots). At KPBS, we established replicate plots in experimental watersheds burned every 1 and 4 years in the spring, and those left unburned (N=9 plots). Thus, the only difference in design between NA and SA was the intermediate burn frequency. In 2005 at both sites we established four 2x2m areas in each replicate of the 1-yr, 3-4 yr burned, and unburned plots (N=36 subplots). We then randomly selected two of the subplots for the fertilization treatment and the other two subplots served as controls (Fig. 1). Starting in 2006 at KPBS and 2007 at URF, we began adding 10 gN/m2/yr as NH4+NO3- to assess the interactive effects of fire frequency and nitrogen limitation on plant community composition, structure and dynamics.
Fig. 1. Experimental design and sampling for the proposed studies: A) the role of long-term fire regimes (without megaherbivores), B) the importance of grazing and grazing/fire interactions, and C) the role of megaherbivore diversity. Moveable exclosures (3/plot) will be used to estimate ANPP in the grazed plots. N addition subplots (2 x 2 m) will be divided into 4 1 x 1 plots, with two designated for plant species composition sampling and the other two for destructive sampling. Soil samples will be collected from areas not designated for ANPP or plant composition sampling. Note that the same annually and infrequently burned plots at Kruger and Konza will be used in (B) and (C). In addition, similar plots will be established minus the N addition subplots in the 1-yr and 4-yr burned blocks of the Buffalo enclosure for (C).
Each of the 2x2m subplots was divided into four 1x1m quadrats. Annually since 2005 (prior to nitrogen addition) canopy cover of each species rooted in each quadrat was visually estimated twice during the growing season to sample early and late season species. As a surrogate for aboveground production, we measured light availability at the end of the growing season above the canopy at the ground surface in each quadrat (N=4 per subplot) using a Decagon ceptometer.
Net primary production measurements: Prior to the 2005 growing season we established plots (13.7 m by 18.3 m) in ungrazed areas burned annually, at 3–4-year intervals, and unburned (n = 3 per fire treatment) at both KBPS and URF. Areas with trees or large shrubs were avoided as our main goal was to evaluate responses in the herbaceous plant community. ANPP was estimated from end-of-season harvests starting in 2005 (September for KBPS, April for URF). In 10, 0.1-m2 (20 cm by 50 cm) quadrats randomly located in each plot (n = 30/treatment/site), we harvested the vegetation at ground level and separated it into grass, forb, and previous year’s dead biomass. Samples were dried at 60C to a constant weight. For annually burned plots, total biomass harvested represents ANPP. For the intermediate and unburned sites, we calculated ANPP by summing all but the previous year’s dead component.
To assess the impacts of fire on ANPP in grazed areas, we established herbivore exclusion treatments in KBPS in North America and KNP in South Africa. Herbivore exclosures in grazed areas in KPBS and KNP were erected prior to the 2006 growing season. The exclosures were 7 m in diameter, 2 m tall, and constructed of diamond mesh (5-cm diameter). Seven exclosures were established in each of three blocks of the three fire treatments— annually burned, intermediate burn (3- years for KNP or 4-years for KPBS), and unburned (n = 21 exclosures/treatment/site). As our focus was on ANPP responses of the herbaceous layer, exclosures were not located beneath trees or where dense shrub patches were present. Additionally, in the Satara region of KNP is a 900-ha permanent enclosure containing 80–90 adult African buffalo (S. caffer). This enclosure was erected in 2000 and was divided into six areas (100–200 ha each), with these burned on a rotational basis including plots burned annually and plots that were unburned. We used the unburned and annually burned areas in the buffalo enclosure to provide a direct comparison for determining the effects of a single-species large grazer in KNP and KPBS, and to assess the effects of large herbivore diversity at adjacent sites in KNP. Similar exclosures were built in the African buffalo enclosure at KNP. We placed 7 exclosures in the three blocks of each fire treatment (annually burned and unburned) resulting in 21 exclosures/treatment. We sampled ANPP by harvesting plant biomass from three 0.1 m2 quadrats per herbivore exclosure at the end of the growing season starting in 2006.
Data are collected twice each year at each site. Sample periods are equivalent to spring and late summer at each study site (December/January and March/April in South Africa, May and September in North America.
Where the Data were Collected:
Ukulinga Research Farm, Pietermaritzburg, South Africa; Satara Region of Kruger National Park, South Africa; Konza Prairie Biological Station, North America
Additional Geographic Metadata:
Ukulinga Research Farm (URF), South Africa. The URF of the University of KwaZulu-Natal is located in Pietermaritzburg, in southeastern South Africa (30o 24’ S, 29o 24’ E). The site is dominated by native perennial C4 grasses, such as Themeda triandra and Heteropogon contortus, that account for much of the herbaceous aboveground net primary production (ANPP). Mean annual precipitation is 790 mm, coming mostly as convective storms during summer (Oct-Apr). Summers are warm with a mean monthly maximum of 26.4oC in February, and winters are mild with occasional frost. Soils are fine-textured and derived from shales. There has been no grazing at this site for >60 years. Long-term experimental plots were established at URF in 1950 with the objective of determining the optimal fire and/or summer cutting regime to maximize hay production. The experiment is a randomized block (three replicates) split-plot design with four whole-plot haying treatments and 11 subplot fire or mowing treatments. Subplot sizes are 13.7 x 18.3 m.
Kruger National Park (KNP), South Africa. The KNP is a 2 million ha protected area of savanna grassland that includes many of the large herbivores common to southern Africa (22º 25' to 25º 2 32' S, 30º 50' to 32º 2' E). The extant abundance and grazing intensity of herbivores in KNP is considered moderate for regional savanna grasslands. In the south-central region of KNP where our research takes place, average rainfall is 537 mm with most falling during the growing season (Oct-Apr). The dormant season is mild, dry and frost free, and summers are warm with mean monthly maximum air temperature of 28.9oC in January. Because of the importance of fire in savanna grassland ecosystems, the Experimental Burn Plot (EBP) experiment was initiated in 1954 to examine the effects of fire frequency (control-no fire, 1-, 2-, 3-, 4- and 6-yr return interval) and season [early spring (Aug), spring (Oct), mid-summer (Dec), late summer (Feb), and fall (Apr)] on vegetation communities in the park. Four blocks of 12 plots (two were later split for the 4- and 6-yr trts), each ~7 ha (370 x 180 m) in size, were established in four primary vegetation types covering the two major soil types (granites and basalts) and spanning the precipitation gradient in the park. Each plot has 50+ years of known fire history, and native herbivores have had unrestricted access, thus fire and grazing effects are combined. This research focuses on the EBPs located near Satara where precipitation, soil type, and the mix of herbaceous and woody plants are similar to KPBS. Vegetation on the blocks is co-dominated by C4 grasses, such as Bothriochloa radicans, Panicum coloratum and Digiteria eriantha, and woody plants, such as Acacia nigrescens and Sclerocarya birrea. Soils are fine-textured and derived from basalts. Adjacent to one of the Satara blocks is the Cape buffalo enclosure, erected in 2000 for veterinary purposes. The 200 ha permanent enclosure contains 65-80 animals and is divided into 4 blocks burned on a rotational basis. The grazing intensity inside is comparable to the moderate levels imposed in the park and at KPBS. Two blocks are burned annually while others are burned infrequently (approximately once every 4-yr).
Konza Prairie Biological Station (KPBS), North America. The KPBS is a 3,487 ha savanna grassland in northeastern Kansas, USA (39o 05’ N, 96o 35’ W) dominated by native perennial C4 grasses such as Andropogon gerardii and Sorghastrum nutans that account for the majority of ANPP. Scattered shrub and tree species include Cornus drummondii, Gleditsia triacanthos, and Prunus spp. Numerous sub-dominant grasses and forbs contribute to the floristic diversity of the site. The climate is continental, with mean July air temperature of 27°C. Annual precipitation is ca. 820 mm/year, with 75% falling as rain during the Apr-Oct growing season. Soils are fine textured, silty clay loams derived from limestone and shales. KPBS includes fully replicated watershed-level fire and fire/grazing treatments, in place since 1977 and 1987, respectively. Replicate watersheds (mean size ~60ha) are burned at 1-, 2-, 4-, 10- and 20-yr intervals, mainly in April, to encompass a range of likely natural fire frequencies and management practices. A subset of watersheds has not been grazed for more than 30 years. To address the role of native grazers and fire/grazing interactions, bison (~260 individuals) were reintroduced to KPBS in a 1000-ha fenced area that includes replicate watersheds burned in the spring at 1-, 2-, 4- and 20-year intervals. The overall grazing intensity is considered moderate.
Study Area 1:
Study Area Name: Ukulinga Research Farm
Study Area Location: Near Pietermaritzburg, South Africa
Elevation: 840 m above sea level
Landform: Colluvium fan
Geology: Marine shales and dolerite colluvium
Soils: Dystric leptosols, Chromic luvisols, Haplic plinthisols
Vegetation: Native grassland
Climate: Mean annual precipitation is 844 mm, Mean annual temperature 17.6C
Site history: Ungrazed since 1950
Single Point: 29o 40’ S / 30o 20’ E
Study Area 2: Kruger National Park, South Africa
Study Area Name: Satara Experimental Burn Plots and Cape Buffalo Exclosure
Study Area Location: Near Satara rest camp
Elevation: 240-320 meters above sea level
Landform: Level Upland
Soils: Rhodic nitisols, Haplic luvisols, Leptic phaeozems
Climate: Mean annual precipitation 544 mm; mean annual temperature 21.2–23.3C
Site history: Grazed by native herbivores
Single Point: 23–25o S /30-31o E
Study Area 3: Konza Prairie Biological Station
Study Area Name: Konza Prairie
Study Area Location: Watersheds N20B, N4D, N1B, N4B; 1D, 4F, 20B
Elevation: 320-444 meters above sea level
Landform: Alluvial terrace
Geology: Cherty limestone and shale
Soils: Udic argiustolls
Climate: Mean annual precipitation 835 mm; mean annual temperature 12.7C
Site history: Ungrazed watersheds (since 1971), watersheds grazed by native herbivores (since 1987)
Single Point: 39o 05.48’ N / 96o 34.12’ W
Konza-Ukulinga fire by nitrogen project: We used comparable experimental designs and sampling procedures at both URF and KPBS (Figure 1). At URF we used three replicate plots (not hayed or mowed) that have been burned every 1 and 3 years in the spring, and those left unburned (N=9 plots). At KPBS, we established replicate plots in experimental watersheds burned every 1 and 4 years in the spring, and those left unburned (N=9 plots). Thus, the only difference in design between NA and SA was the intermediate burn frequency. In 2005 at both sites we established four 2x2m areas in each replicate of the 1-yr, 3-4 yr burned, and unburned plots (N=36 subplots). We then randomly selected two of the subplots for the fertilization treatment and the other two subplots served as controls (Fig. 1). Starting in 2006 at KPBS and 2007 at URF, we began adding 10 gN/m2/yr as NH4+NO3- to assess the interactive effects of fire frequency and nitrogen limitation on plant community composition, structure and dynamics.
Konza-Kruger fire by grazing project: For this study, we are utilizing the long-term experiments at KPBS and KNP in which native megaherbivore grazers are present and fire frequency is directly manipulated. To assess the effects of grazing and fire-grazing interactions, we constructed seven sets of permanent exclosures and adjacent control plots in three blocks at both sites. The exclosures and matching paired open plots were established in 2005 in the Satara EBPs that are burned every 1 and 3 years in the spring or left unburned and at KPBS in watersheds that are burned every 1 and 4 years or left unburned. (N=63 exclosures/site; Fig. 1). Within each exclosure and paired open plot, we sample plant community composition and light availability in permanent 2x2 m subplots. We collect ANPP at the end of each growing season from each exclosure, and throughout the growing season in grazed areas adjacent to the unexclosed plots using 1x1 m moveable exclosures (Fig. 1).
The Sevilleta Gunnison’s Prairie Dog (Cynomys gunnisoni) Restoration project examines keystone consumer (herbivore) effects on grassland in concert with ecological restoration of a “species of greatest conservation need in New Mexico” (NMG&F Comprehensive Wildlife Conservation Strategy, 2007). SevLTER partners directly with Sevilleta National Wildlife Refuge, New Mexico Game and Fish, USFS Rocky Mountain Research Station and non-profit Prairie Dog Pals on this ambitious effort to re-establish Gunnison’s prairie dogs to blue grama dominated (Bouteloua gracilis) Great Plains grassland at the foothills of the Los Pinos Mountains on Sevilleta. While engaged in wildlife management aimed at translocation of approximately 3000 individual prairie dogs, ultimately establishing 5-6 colonies over a 500 ha area, SevLTER is focusing resources on monitoring population dynamics of reintroduced prairie dogs and their effects on vegetation production and diversity, soil disturbance and grasshopper community composition. In this experiment, prairie dogs act as the treatment on a grassland site where the species was extirpated 40 years ago. The long term nature of the project lies in the course of re-establishing prairie dogs combined with the ultimate research goal of describing the functional role of Gunnison’s prairie dogs in an arid grassland ecosystem: first we are challenged to develop and document an economical and efficient management strategy which maximizes reintroduction success and colony survival; second we are tasked with monitoring prairie dog dynamics and their effects on the grassland throughout re-establishment and into a future state, when presumably management intervention will have subsided and we characterize the ecosystem as ‘restored’ – both in the face of highly variable abiotic inputs such as precipitation and temperature and biotic impacts such as predation.
Prairie dogs will be sampled using mark-re-sight methods in the spring (last week of March) and summer (3rd week of June) each year. The justification for this sampling period is to understand overwinter survival and offspring recruitment.
Mark Re-sight Methodology
Prebaiting and Observation Towers
Prior to any trapping, traps in the field are checked to make sure all wooden covers are in place, if not, traps should be repaired as needed. Set 100 traps within each 100m x 100m trapping area. Place traps near active burrows 4 days prior to trapping. At this time trap doors are wired open (make certain all traps are properly wired open) with bait trailing from the outside into the back of (or through) the trap. Traps are baited with sweet feed. Make sure that all traps are functioning properly by testing the trap door sensitivity and adjusting with pliers if needed. Pre-bait traps every morning for 3 sequential days total. All traps should be GPSed and have an adjacent numbered flag and tape with a corresponding number located on the trap.
On the morning of the fourth day, well before sunrise, the wires are removed from the traps and the traps then set and baited to capture animals. The traps are all opened well before sunrise, so animals are not disturbed by human activity. This is very important. Prairie dogs are trapped for 3 consecutive mornings. Traps are only left opened during the early morning period, until about 10:00 or 11:00 am, depending on the weather conditions and time of year. Prairie dog activity declines by 10:00-11:00, so even if the weather conditions are fine for continued trapping, trap success after this time will decline dramatically. Traps are collected by around 9:00 am, depending on the weather conditions and time of year, and all trapped animals are brought to a common processing station. At the processing station the trap location, ear tag number, sex, weight, and age of the animal are recorded. It is indicated if the animal is new or a re-capture during this trapping period. If no ear tags are present, new ear tags are clipped to both ears, and the numbers recorded. If one ear tag is missing, another is added to the ear with no tag, and the number recorded. All animals are marked with Nyanzol black dye. For our purposes, it is not necessary to mark each animal with numbers. The goal is to make sure each animal has a clear black mark on its back. Animals at the processing site are kept at all times in the shade and carrots should be given to provide moisture during the heat and stress. Once animals have been processed they are released into their burrow, at the location of their capture. All traps are closed for the day. To make sure all are closed, one person closes all the traps from one of the plots and mark the number on the GPS sheet to note the trap has been closed.
Additional Study Area Information
Study Area Name: Prairie Dog Town
Study Area Location: The study area is about 655 ha (~2.5 sq mi) in size and approximately1 km due west from the foothills of the Los Pinos Mountains. The study is also just north of the Blue Grama Core Site.Elevation: 1670 mSoils: sandy loam and sandy clay loamSite history: historically large prairie dog colonies inhabited the study area
Plant phenology or life-history pattern changes seasonally as plants grow, mature, flower, and produce fruit and seeds. Plant phenology follows seasonal patterns, yet annual variation may occur due to annual differences in the timing of rainfall and ambient temperature shifts. Foliage growth and fruit and seed production are important aspects of plant population dynamics and food resource availability for animals.
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