biology

Warming-El Nino-Nitrogen Deposition Experiment (WENNDEx): Soil Temperature, Moisture, and Carbon Dioxide Data from the Sevilleta National Wildlife Refuge, New Mexico (2011 - present)

Abstract: 

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.

Core Areas: 

Data set ID: 

305

Keywords: 

Methods: 

Experimental Design

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 Measurements

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).

Data sources: 

sev305_wenndex_soiltemp_moisture_co2_2011
sev305_wenndex_soiltemp_moisture_co2_2012
sev305_wenndex_soiltemp_moisture_co2_2013
sev305_wenndex_soiltemp_moisture_co2_2014
sev305_wenndex_soiltemp_moisture_co2_2015

Instrumentation: 

Instrument Name: Solid State Soil CO2 sensor
Manufacturer: Vaisala
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

Monsoon Rainfall Manipulation Experiment (MRME) Soil Temperature, Moisture and Carbon Dioxide Data from the Sevilleta National Wildlife Refuge, New Mexico (2012- present)

Abstract: 

The Monsoon Rainfall Manipulation Experiment (MRME) is designed to understand changes in ecosystem structure and function of a semiarid grassland caused by increased precipitation variability, by altering rainfall pulses, and thus soil moisture, that drive primary productivity, community composition, and ecosystem functioning. The overarching hypothesis being tested is that changes in event size and frequency will alter grassland productivity, ecosystem processes, and plant community dynamics. Treatments include (1) a monthly addition of 20 mm of rain in addition to ambient, and a weekly addition of 5 mm of rain in addition to ambient during the months of July, August and September. It is predicted that changes in event size and variability will alter grassland productivity, ecosystem processes, and plant community dynamics. In particular, we predict that many small events will increase soil CO2 effluxes by stimulating microbial processes but not plant growth, whereas a small number of large events will increase aboveground NPP and soil respiration by providing sufficient deep soil moisture to sustain plant growth for longer periods of time during the summer monsoon.

Core Areas: 

Data set ID: 

304

Keywords: 

Methods: 

Experimental Design

MRME contains three ambient precipitation plots and five replicates of the following treatments: 1) ambient plus a weekly addition of 5 mm rainfall, 2) ambient plus a monthly addition of 20 mm rainfall. Rainfall is added during the monsoon season (July-Sept) by an overhead (7 m) system fitted with sprinkler heads that deliver rainfall quality droplets. At the end of the summer, each treatment has received the same total amount of added precipitation, delivered in different sized events. Each plot (9x14 m) includes subplots (2x2 m) that receive 50 kg N ha-1 y-1. Each year we measure: (1) seasonal (July, August, September, and October) soil N, (2) plant species composition and ANPP, (3) annual belowground production in permanently located root ingrowth cores, and (4) soil temperature, moisture and CO2 fluxes (using in situ solid state CO2 sensors).

Soil Measurements

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).

Data sources: 

sev304_mrme_soiltemp_moisture_co2_2012
sev304_mrme_soiltemp_moisture_co2_2013
sev304_mrme_soiltemp_moisture_co2_2014
sev304_mrme_soiltemp_moisture_co2_2015

Instrumentation: 

Instrument Name: Solid State Soil CO2 sensor
Manufacturer: Vaisala
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

Additional information: 

Additional Study Area Information

Study Area Name: Monsoon site

Study Area Location: Monsoon site is located just North of the grassland Drought plots

Vegetation: dominated by black grama (Bouteloua eriopoda), and other highly prevalent grasses include Sporabolus contractus, S.cryptandrus, S. lexuosus, Muhlenbergia aernicola and Bouteloua gracilis.

North Coordinate:34.20143
South Coordinate:34.20143
East Coordinate:106.41489
West Coordinate:106.41489

Extreme Drought in Grassland Ecosystems (EDGE) Seasonal Biomass and Seasonal and Annual NPP Data at the Sevilleta National Wildlife Refuge, New Mexico (2013- present)

Abstract: 

Net primary production is a fundamental ecological variable that quantifies rates of carbon consumption and fixation. Estimates of NPP are important in understanding energy flow at a community level as well as spatial and temporal responses to a range of ecological processes.  While measures of both below- and above-ground biomass are important in estimating total NPP, this study focuses on above-ground net primary production (ANPP). Above-ground net primary production is the change in plant biomass, including loss to death and decomposition, over a given period of time. Volumetric measurements are made using vegetation data from permanent plots collected in SEV297, "Extreme Drought in Grassland Ecosystems (EDGE) Net Primary Production Quadrat Data" and regressions correlating biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."

Data set ID: 

298

Core Areas: 

Additional Project roles: 

469

Keywords: 

Methods: 

Derivation of Biomass and Net primary Production:

Data from SEV297 and SEV157 are used to calculate the seasonal and annual production (i.e., biomass) of each species in each quadrat for a given year. Allometric equations derived from harvested samples of each species for each season are applied to the measured cover, height, and count of each species in each quadrat. This provides seasonal biomass for winter, spring, and fall.

Seasonal net primary production (NPP) is derived by subtracting the previous season's biomass from the biomass for the current season. For example, spring NPP is calculated by subtracting the winter weight from the spring weight for each species in a given quadrat. Negative differences are considered to be 0. Likewise, fall production is computed by subtracting spring biomass from fall biomass. Annual biomass is taken as the sum of spring and fall NPP.

Data sources: 

sev298_edgebiomass_20150818

Additional information: 

The bounding box coordinates for the corners of the polygon which encompasses the full EDGE black site are:NW: -106.729227  34.337913 Decimal DegreesNE: -106.728434  34.337937 Decimal DegreesSW: -106.729144  34.337298 Decimal DegreesSE: -106.728392  34.337310 Decimal DegreesEDGE blue:NW: -106.622610  34.342141 Decimal DegreesNE: -106.621689  34.342079 Decimal DegreesSW: -106.623365  34.341518 Decimal DegreesSE: -106.622711  34.341015 Decimal Degrees

Response of Vegetation and Microbial Communities to Monsoon Precipitation Manipulation in a Mixed Blue and Black Grama Grassland at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

The purpose of this project is to test the hypothesis that the smallest 50% of precipitation events during the monsoon season affect microbial functioning and grassland productivity in mixed grasslands of B.eriopoda and B. gracilis at the SNWR. At the SNWR, the summer monsoon season accounts for 60% of total annual precipitation and drives the majority of vegetation productivity during the year; the largest 25% of precipitation events account for the majority of this precipitation. I predict that important ecological variables such as nutrient and soil moisture availability are disproportionately influenced by smaller events. The proposed project will help tease apart the importance of precipitation event classes on nutrient availability and grassland aboveground net primary production (ANPP). This research will also provide a basis for understanding how increased aridity in the U.S. southwest due to increasing global surface temperature and altered precipitation could affect grassland communities at the SNWR.

Additional Project roles: 

34
35

Data set ID: 

286

Core Areas: 

Keywords: 

Methods: 

We will implement 10 open plots (control) and 10 precipitation exclosure plots(treatment; 20 total plots) at a mixed blue and black grama grassland site at the SNWR. In this experiment, treatment plots will only receive the largest 50% of precipitation events. This will maintain statistically similar total precipitation between control and treatment plots because the smallest 50% of events have an insignificant effect on total seasonal precipitation. How these small events are linked to microbial activity and vegetation productivity is still very much unknown. I predict that soil microbial activity and nutrient availability will differ between control and treatment plots and will result in differing vegetation ANPP between them. These effects may become more distinct as time progresses, which is the reason for conducting this research for a series of monsoon seasons.

Existing precipitation exclosures (2.45 m x 2.45 m) will be employed at the mixed grassland site. We will implement 20 total plots (10 control, 10 treatment; approx. 500 m2 total area). Temporary site infrastructure will include 10 precipitation exclosures, a water tank (1100 gal.) and soil moisture probes. This infrastructure currently exists at the mixed grassland site and will be adopted from Michell Thomey's project entitled, "Soil moisture extremes and soil water dynamics across a semiarid grassland ecotone."

Precipitation is the only independent variable in this experiment. Using precipitation exclosures, I will remove all ambient precipitation from treatment plots from DOY 182-273. Ambient daily precipitation thatexceeds the estimated 50% threshold will be delivered to the plots within 24 hours of an event. Delivered precipitation will be adjusted for atmospheric demand differences. 

Dependent variables in this experiment are vegetation ANPP, soil nitrogen content, soil enzymatic activityand soil moisture content. Vegetation biomass will be collected from the sites on DOY 181 and 274. Soil enzymatic activity will be determined approximately 4 times per monsoon season using plot soil samples. Soil nitrogen content will be measured under vegetation using nitrogen probes. Volumetric soil moisture content [m3 m-3] will be measured continuously using soil moisture probes (30 cm depth). 

Water Potential Data From Pinyon-Juniper Forest at Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

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. 

Data set ID: 

285

Additional Project roles: 

30

Core Areas: 

Keywords: 

Methods: 


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.

Instrumentation: 


Instrument Name: thermocouple psychrometer with stainless steel screen

Manufacturer: Wescor, Inc, Logan, UT, USA

Model Number: PST-55

Stress Response from Male-Male Competition in Varying Thermal Environments at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

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.

Additional Project roles: 

32
33

Data set ID: 

284

Core Areas: 

Keywords: 

Methods: 

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).

Konza Species Composition: Fire by Nitrogen Project

Abstract: 

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.

Data set ID: 

268

Core Areas: 

Keywords: 

Methods: 

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. 

Additional information: 

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

Geology: Basalts

Soils: Rhodic nitisols, Haplic luvisols, Leptic phaeozems

Vegetation: Native grassland

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

Vegetation: Native grassland

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

Capital Breeding and Allocation to Life History Demands are Highly Plastic in Lizards at the Sevilleta National Wildlife Refuge, New Mexico: Field Study

Abstract: 

The use of stored resources to fuel reproduction, growth and maintenance to balance variation in nutrient availability is common to many organisms. The degree to which organisms rely upon stored resources in response to varied nutrients, however, is not well quantified. Through stable isotope methods we quantified the use of stored versus incoming nutrients to fuel growth, egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual’s body condition. Furthermore, given sufficient income lizards in poor condition can allocate simultaneously to storage, growth, and reproduction, which allowed them to catch up to better conditioned animals. In a parallel, inter-specific survey of wild lizards we found that the degree of capital breeding varied widely across a diverse community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs, but is a function of the condition state of individuals and the availability of nutrients during both breeding and non-breeding seasons. Here we explore the implications of these findings for our understanding of capital breeding in lizards and the utility and value of the capital-income concept in general.

Data set ID: 

261

Core Areas: 

Keywords: 

Methods: 

Lizard Capture: 

For measures of capital breeding in wild lizards, females of seven species were caught April through July of 2008 under the approval of the University of New Mexico institutional animal care and use committee (UNM-IACUC #05MCC004).  The species captured were: Cophosaurus texanus, Crotaphytus collaris, Eumeces multivirgatus, Phrynosoma modestum, Sceloporus undulates consubrinus, Urosaurus ornatus, and Uta stansburiana.   Lizards deemed by palpation to be egg-bearing were returned to the lab, euthanized and reproductive tissues prepared for stable isotope analysis (see below).  

Stable isotope treatments:

After the lizards were euthanized liver, fat body, and thigh muscle samples were harvested, freeze dried and a 0.5 mg sample was placed into a pre-cleaned tin capsule (Costech, #041074, Valencia, CA) for stable isotope analysis.  Eggs and follicles were also harvested, their length and width measured and freeze dried.  All lipids were extracted from freeze dried and ground muscle and eggs/follicles by a 2:1 chloroform and methanol bath; lizard muscle had undetectable amounts of lipids.  The suspended lipids from eggs were pipetted into separate storage vials and air dried.  Lipids and lipid-free egg tissues were then loaded into tin capsules.  We measured the δ13C of each egg and follicle greater than 6mm in length (½ the length of shelled eggs and assumed to reflect reproductive allocation).  Our stable isotope methodology follows standard methods and our protocol is described in detail in Warne et al. (2010a, 2010b).  We report all isotope values in the standard delta notation (δX = (Rsample /Rstandard – 1) x 1000) in parts per thousand (‰) relative to the international carbon standard VPDB (Vienna Pee Dee Belemnite).  Measurements were conducted on a continuous flow isotope ratio mass spectrometer in the UNM Earth and Planetary Sciences Mass Spectrometry lab.  The precision of these analyses was ± 0.1‰ SD for δ13C based on long-term variation of the working laboratory standard (valine δ13C = -26.3‰ VPDB), samples of which were included on each run in order to make corrections to raw values obtained from the mass spectrometer. 

Essential to this study is the observation that differences in photosynthetic biochemistry inherent to C3- and C4-plants produces distinct differences in the d13C of their tissues, which can be used to trace the movement of nutrients through consumers (Hobson et al. 1997, O'Brien et al. 2000).  Because winter and summer monsoonal rains drive seasonally separated C3 and C4 plant production and resource flux in Chihuahuan Desert food webs (Warne et al. 2010b), we hypothesized that we could use natural variation in the δ13C of C3 and C4 resources to examine capital breeding in wild lizards. We predicted that during the late summer and early fall lizards would develop endogenous lipid stores (capital) from C4 derived sources because C4 plants (primarily grasses) comprise the bulk of primary production during this period.  We also hypothesized that reproduction in the spring (the income source) would be fueled by C3 plants associated with winter rains. We subsequently sampled female lizards of a variety of species during April through June 2008 to gauge the relative use of capital (C4) versus income (C3) resources for their first clutch of the season.  The lizards were collected from a mixed Creosote and gramma grassland. 

We used tissue d13C values and a standard two-end-point mixing model to estimate the proportion of endogenous fat or muscle (capital) and incoming insect-dietary sources used to provision eggs.  The mean δ13C value of insects feeding on C3 plants (-27.3‰) served as an income source (see Warne et al. 2010b).  The discrimination (Δ13C) values used in this model for muscle (-1.9‰) and fat bodies (0‰) were experimentally determined for S. undulatus (Warne et al. 2010a).  

Additional information: 

 Study Area 1:  

*Study Area Name:  Socorro NM

*Study Area Location:  BLM land 11 miles south of Socorro, NM

*Study Area Description:  Mixed creosote and gramma grass shrubland

*GPS Coordinates:  

North Coordinate:  33°56'54.88"N

West Coordinate: 106°57'6.26"W

Study Area 2:  

*Study Area Name:  Tres pistoles 

*Study Area Location:  BLM land 13 miles east of Albuquerque, NM

*Study Area Description:  Mixed shrub and gramma grassland

*GPS Coordinates:  

North Coordinate:  35° 4'44.38"N

West Coordinate: 106°26'48.29"W

Capital Breeding and Allocation to Life History Demands are Highly Plastic in Lizards at the Sevilleta National Wildlife Refuge, New Mexico: Experimental Study

Abstract: 

The use of stored resources to fuel reproduction, growth and maintenance to balance variation in nutrient availability is common to many organisms. The degree to which organisms rely upon stored resources in response to varied nutrients, however, is not well quantified. Through stable isotope methods we quantified the use of stored versus incoming nutrients to fuel growth, egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual’s body condition. Furthermore, given sufficient income lizards in poor condition can allocate simultaneously to storage, growth, and reproduction, which allowed them to catch up to better conditioned animals. In a parallel, inter-specific survey of wild lizards we found that the degree of capital breeding varied widely across a diverse community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs, but is a function of the condition state of individuals and the availability of nutrients during both breeding and non-breeding seasons. Here we explore the implications of these findings for our understanding of capital breeding in lizards and the utility and value of the capital-income concept in general. 

Core Areas: 

Data set ID: 

260

Keywords: 

Methods: 

Lizard Capture and Maintenance:

Thirty two female prairie lizards (Sceloporus undulatus) were caught on Bureau of Land Management reserves near Albuquerque, NM during the last two weeks of July, 2007 and maintained in a room at the biology department of the University of New Mexico under the approval of the UNM-IACUC (#07UNM007).   Two lizards were housed per 20 gallon glass terrarium and were provided a sand substrate, as well as perch and shelter spaces built by stacked pieces of plywood and rock.  Lizards were kept on a 12 hour (light:dark) photoperiod and a temperature gradient was provided by a 100 watt heat lamp placed at one end of the terrarium and focused on the wood perch, which provided a stable heat gradient that ranged from 39 ± 1.7ºC at the perch to 26 ± 0.8ºC at the cool end of the tank.  Resulting mean daytime body temperatures were 36.3 ± 6.2ºC (n = 18).  An ultraviolet-B fluorescent light (ZooMed® UVB 10.0 fluorescent) was also provided for vitamin D synthesis. 

Experimental dietary treatments and reproduction:

S. undulatus were captured from a cottonwood woodland field site and paired by Snout Vent Length (SVL) and then randomly split into either a high (n = 16) or low nutrient treatment (n = 16).  The high nutrient diet consisted of seven crickets and two mealworms per week; similar to an ad libitum diet found by Angilletta (2001).  We estimated that a low nutrient diet reduced by ~30% of ad libitum (five crickets/week and one mealworm every other week) would reduce body condition and reflect the poor conditions experienced by lizards in the wild (see Ballinger 1977, 1979, Ballinger and Congdon 1980, Sinervo and Adolph 1994).   These low diet lizards were switched to the high diet after hibernation, referred to hereafter as the LH treatment (n = 16).   The high treatment prior to hibernation was split into a high diet post-hibernation (HH, n = 8) and a low treatment (HL, n = 8).  We did not have an LL treatment because we assumed that they would be in such low body condition that they would not reproduce.

The lizards were prepared for hibernation during November 2007 by gradually reducing the photoperiod to 7 hours per day, and were fasted for two weeks. Lizards were then placed in 27 liter plastic containers with a sandy substrate and wood shavings for burrowing on November 17, 2007 and maintained at 10.2 ± 3.1ºC.  The lizards were removed from hibernation on February 2, 2008. To induce reproduction, male prairie lizards that were maintained for a separate study were introduced for two weeks to the female terrarium in mid-February of 2008.  Reproduction was observed in numerous tanks (mounting and copulation), and signs of reproduction (bite marks) were apparent on all females. The female lizards were then palpated weekly to monitor egg development.  When eggs appeared to be nearly shelled or shelled, the lizards were euthanized via an intraperitoneal injection of sodium pentobarbital (using a dose of 60 mg/kg).   Two lizards were euthanized in late March following rapid development of shelled eggs.  All other lizards were euthanized during the last week of May 2008, at which time most were found to have either large follicles or shelled eggs. 

Stable isotope treatments:

After the lizards were euthanized liver, fat body, and thigh muscle samples were harvested, freeze dried and a 0.5 mg sample was placed into a pre-cleaned tin capsule (Costech, #041074, Valencia, CA) for stable isotope analysis.  Eggs and follicles were also harvested, their length and width measured and freeze dried.  All lipids were extracted from freeze dried and ground muscle and eggs/follicles by a 2:1 chloroform and methanol bath; lizard muscle had undetectable amounts of lipids.  The suspended lipids from eggs were pipetted into separate storage vials and air dried.  Lipids and lipid-free egg tissues were then loaded into tin capsules.  We measured the δ13C of each egg and follicle greater than 6mm in length (½ the length of shelled eggs and assumed to reflect reproductive allocation).  Our stable isotope methodology follows standard methods and our protocol is described in detail in Warne et al. (2010a, 2010b).  We report all isotope values in the standard delta notation (δX = (Rsample /Rstandard – 1) x 1000) in parts per thousand (‰) relative to the international carbon standard VPDB (Vienna Pee Dee Belemnite).  Measurements were conducted on a continuous flow isotope ratio mass spectrometer in the UNM Earth and Planetary Sciences Mass Spectrometry lab.  The precision of these analyses was ± 0.1‰ SD for δ13C based on long-term variation of the working laboratory standard (valine δ13C = -26.3‰ VPDB), samples of which were included on each run in order to make corrections to raw values obtained from the mass spectrometer. 

Essential to this study is the observation that differences in photosynthetic biochemistry inherent to C3- and C4-plants produces distinct differences in the d13C of their tissues, which can be used to trace the movement of nutrients through consumers (Hobson et al. 1997, O'Brien et al. 2000).  The lizards were collected from cottonwood woodlands in which their diet was largely composed of C3-plant derived carbon, as evidenced by a baseline muscle δ13C of -25.1± 0.1‰ VPDB, near that of the mean value for C3 plants of -27.3 ± 0.04‰.  Prior to hibernation lizards were maintained on a diet composed of crickets (mean δ13C ± SEM for lipids = -22.5 ± 0.1‰ and lipid free carbon = -21.7 ± 0.1‰ VPDB, n = 16) raised on C3-plant derived dog food (Nutro® Natural Choice® large breed puppy lamb and rice formula) and mealworms (lipids = -26.3 ± 0.1‰ and lipid free = -24.35 ± 0.1‰ VPDB, n = 8) raised on bran meal.  Here we used the mathematical normalization model of Post et al. (2007) to determine the lipid-free δ13C values for these insects, assuming reported lipid contents of 13.8% for crickets and 32.8% for mealworms (Bernard and Allen 1997).  Maintaining lizards on a C3 diet prior to hibernation insured that their capital stores of fat bodies and muscle would have consistent carbon isotope values.  After hibernation the lizards were switched to a C4 based insect diet of crickets (lipids = -16.3 ± 0.1‰ and lipid free = -15.53 ± 0.1‰VPDB, n = 35) raised on a C4 - corn based dog food (Iams® Smart Puppy large breed formulaTM) and mealworms (lipids = -13.0 ± 0.3‰ and lipid free = -10.2 ± 0.2‰ VPDB, n = 9) raised on coarse ground cornmeal; which provided an ‘income’ diet with δ13C values distinct from the pre-hibernation C3 diet.   

We used tissue d13C values and a standard two-end-point mixing model to estimate the proportion of endogenous fat or muscle (capital) and incoming insect-dietary sources used to provision eggs.  Because crickets and mealworms had different δ13C values and the dietary treatments imposed on the lizards also consisted of differing quantities of feeder insects (high = 7 crickets + 2 mealworms/week; low = 5 + 0.5/week) we used a weighted mean to calculate the insect δ13C for each treatment in this model.   The weighted δ13C value for the high dietary treatment for C4 insect lipids was -15.6‰ and -14.3 for lipid free carbon; for the low treatment C4 insect lipids was -16‰ and -15‰ for lipid-free carbon.  The discrimination (Δ13C) values used in this model for muscle (-1.9‰) and fat bodies (0‰) were experimentally determined for S. undulatus (Warne et al. 2010a).  

Statistical analysis:

The effect of dietary treatment on the body condition of lizards was analyzed by repeated measures ANCOVA with treatment and stage of the experiment as fixed effects, individuals as random effects nested within treatment, and snout-vent length (SVL) as a covariate.  Body condition was estimated as the least squares (LS) mean of body weight (minus eggs) adjusted for SVL in this ANCOVA model; a method argued to be more statistically sound than other condition indices (Packard and Boardman 1988, García-Berthou 2001).  Treatment effects on SVL were similarly analyzed by repeated measures ANOVA.  Mauchly’s test was used to confirm that the assumption of sphericity for repeated measures analysis was valid, and epsilon corrections to the degrees of freedom were applied when necessary.   Dietary treatment effects on growth were measured by the specific growth rate of SVL (ln(SVL2/SVL1)/Δdays) for the pre- and post hibernation periods, and analyzed by one-way ANOVA.   Dietary treatment effects on reproductive effort, measured as relative clutch mass (RCM = clutch mass/body mass with no eggs) and clutch size were analyzed by one-way ANOVA.  The effect of dietary treatment on tissue δ13C values were similarly analyzed by one-way ANOVA.  Post-hoc comparisons of treatment effects during the four experimental stages were conducted using Tukey-Kramer’s HSD test.  Prior to all analyses the data were tested for homogeneity of variance and confirmed to meet model assumptions.  These analyses were performed in JMP® 8.0 (SAS Institute Inc., Cary, NC, 1989-2007).  All values are reported as mean ± SEM.

Piñon Pine (Pinus edulis) Responses of Annual Growth to Water Availability in a Pinyon-Juniper Forest at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

Increased incidence of large-scale forest die-off attributed to drought has been observed globally over the past decade, raising concern about the future stability of forests as carbon sinks.  To understand the mechanistic basis of semi-arid woodland responses to drought, we measured annual increment growth from branches of Pinus edulis in a rainfall manipulation experiment at the Sevilleta National Wildlife Refuge and LTER site in central New Mexico, USA. We collected 4 branches from each of five trees growing in drought, irrigation, cover control, and ambient control plots at a site in the Los Pinos Mountains.  We measured annual branch elongation, stem diameter, sapwood area, and leaf area.  We compared these structural data to fluctuations in annual precipitation across treatments to understand how such variation in available water influence branch growth.  Rainfall manipulation produced clear differences among treatment groups, with drought trees exhibiting shorter stem lengths, decreased stem and sapwood diameters, and decreased leaf area production than control treatments.  Irrigated trees displayed increased stem length, stem diameter, sapwood diameter, and leaf area production relative to ambient controls.  The net effect of these responses is a likely shift in the allometric relationships, such as hydroactive xylem and absorbing root area.

Additional Project roles: 

18
19
20

Data set ID: 

248

Core Areas: 

Keywords: 

Methods: 

Branch sampling, four small branches were removed from each of five target trees per plot according to aspect (North, South, East, West). 

Experimental design:  Single block from complete block design.

Plots:  Four plots of varying treatments (Irrigation, Drought, Cover control, Ambient control) were used from preexisting study, each 40m X 40m.

Sampling:  Samples taken according to aspect (North, South, East, West) on all pinon target trees within one replicate block.

Measurements:  Stem length, two perpendicular midpoint diameter, and two perpendicular sapwood diameters were taken for each growth increment for each sample using digital callipers. Needles from each age cohort were scanned and leaf area was estimated using ImageJ software.

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