Resource Allocation and Allometry of Plant Growth at Selected Sites in the Arctic: 2003-2005 Growing Seasons

Summary

This data set consists of seven data files containing measurements from Arctic field sites during the summer months from 5 July 2003 to 5 August 2005 as part of the Land-Atmosphere-Ice Interactions (LAII) International Tundra Experiment (ITEX). Investigators designed this research, which compares an extensive range of vegetation types that exists in widely-separated sites, to help identify the relative vulnerability of different vegetation types, plant functional types, and species to climate change and other forms of disturbances. They evaluated specific parameters to improve understanding of the broad patterns of vegetation change and vegetation function across the Arctic and quantify the constraints on the patterns of growth of arctic-plant feedbacks to the Arctic System. The research sites are located in Alaska, USA; Abisko, Sweden; and Svalbard, Norway.

Data are in Microsoft Excel (.xls) format, viewable with spreadsheet software. Data are distributed as an approximately 575 KB compressed file and are available via FTP.

Citing These Data

Shaver, G., and L. Street. 2006. Resource allocation and allometry of plant growth at selected sites in the Arctic: 2003-2005 growing seasons. Boulder, Colorado USA: National Center for Atmospheric Research, ARCSS Data Archive.

Overview Table

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigators

Gaius Shaver
Marine Biological Laboratory
The Ecosystem Center 7 MBL Street
Woods Hole, MA 02543 USA

Lorna Street
Marine Biological Laboratory
The Ecosystem Center 7 MBL Street
Woods Hole, MA 02543 USA

Acknowledgements

This research was funded by the National Science Foundation (NSF) Office of Polar Programs (OPP) grant 0352897 to Gaius Shaver.

2. Detailed Data Description

Format

Data are in Microsoft Excel (.xls) format and are viewable with spreadsheet software.

File and Directory Structure

Click on the record title to view the structure of each data file.

File Size

Data files range from 30 KB to 1.03 MB.

Spatial Coverage

Toolik Lake, Alaska USA:
     Latitude: 68.6334° N
     Longitude: 149.5667° W

Imnavait Creek, Alaska USA:
     Latitude: 68.6167° N
     Longitude: 149.3000° W

STEPPS site, Abisko Sweden:
     Latitude: 68.3000° N
     Longitude: 18.8500° E

Paddus, Abisko Sweden:
     Latitude: 68.3167° N
     Longitude: 18.8500° E

Latnjajaure, Abisko Sweden:
     Latitude: 68.3500° N
     Longitude: 18.8500° E

Adventdalen, Svalbard Norway:
     Latitude: 78.2167° N
     Longitude: 15.6334° E

Temporal Coverage

Investigators collected data during the summer months from 5 July 2003 to 5 August 2005.

Parameter or Variable

Investigators designed this research as a search for the general characteristics of plant growth, resource allocation, and allometry to be used in the development of large-scale, long-term predictions of vegetation properties and of the role of arctic vegetation in the Arctic System. They evaluated primary production, carbon fluxes, nitrogen turnover, normalized difference vegetation index (NDVI), and canopy structure, all key components of the feedbacks and interactions between the terrestrial landscape and the cycles of energy, water, and elements in the Arctic System. Field research at each site includes quadrant harvests for analysis of production-biomass relationships, biomass allocation patterns, nitrogen turnover and use, and canopy leaf area-leaf nitrogen interactions. All sampling relates these variables to carbon dioxide fluxes, stem density and branching patterns, and NDVI.

Parameters measured for this study include:

• soil temperature
• soil volumetric water content (VWC)
• air pressure
• air temperature
• average chamber CO₂ concentration
• average chamber H₂O concentration
• average photosynthetic active radiation (PAR) level
• maximum PAR
• range of PAR
• normalized difference vegetation index (NDVI)
• net ecosystem productivity (NEP)
• H₂O flux
• ecosystem respiration (Re)
• gross primary productivity (GPP)
• light saturated rate of GPP
• half saturation constant of GPP
• ecosystem light compensation point
• initial light use efficiency
• latitude
• longitude
• elevation
• vegetation description
• species
• functional group
• estimated cover
• percent plant cover by functional type
• point intercept.

Sample Data Record

These data are from point_framing.xls. See ITEX circumarctic CO₂ flux survey: point framing for a description of the data file structure.

3. Data Access and Tools

Data Access

Data are available for ordering through NCAR.

Volume

The entire data set is 1.84 MB uncompressed, but is distributed as an approximately 575 KB compressed file.

See Also

• Arctic Long Term Ecological Research (ARC LTER)
• Snow in Tundra Environments: Patterns, Processes and Scaling (STEPPS)

4. Data Acquisition and Processing

Soil temperatures

Investigators measured soil characteristics every time they collected CO₂ flux data on a plot. They measured soil temperature 5 times per plot at 5 cm and 10 cm below the soil surface using traceable soil temperature probes (Fischer Scientific). Where possible, they acquired 5 thaw depth measurements (Alaska only) and 5 volumetric water content (VWC) measurements from the soil. Investigators used a Hydrosense Water Content Sensor (time domain reflectometry probe, TDR) with 20 cm tines (Campbell Scientific) to measure VWC and inserted the TDR probe into the soil to the full depth of 20 cm whenever possible (If this was not possible, the tines were inserted at an angle.). They indicated the approximate depth in the COMMENTS column of the data file. At times, the soil was too rocky to penetrate for temperature measurements or VWC measurements, indicated in the COMMENTS column of the data file.

Investigators measured thaw depth using a graduated steel rod pushed down through the soil to the top of the permafrost. From the abruptness of change in penetrability of the soil investigators indicated that rock and not permafrost was the underlying material in the COMMENTS column of the data file.

Processing:

The manufacturer calibrated the TDR probe for use in agricultural soils. For tundra soils, meter readings were corrected using the following equation:

actual VWC (%) = 0.5952 * (meter reading) + 7.684
R² = 0.8649 (J. Powers, unpublished data, 2003)

CO2 flux measurements and light response curve parameters

Investigators took 3059 individual CO₂ flux measurements to produce 277 light response curves on 145 plots in northern Alaska, northern Sweden, and Svalbard.

Investigators measured CO₂ and H₂O flux using a LiCor 6400 photosynthesis system (Li-Cor Inc., Lincoln, Nebraska USA) connected to a 1 m x 1 m x 0.25 m plexiglass chamber. At the Alaska sites in the late summer of 2003 and 2004, they used a LiCor 2600 photosynthesis system (Note: The LiCor 6200 does not measure air pressure; estimates from Toolik weather station data are used with correction for altitude at Imnavait). Measurements made with the 6200 system are corrected for effects of water vapor flux using protocols recommended by Hooper et al. 2002.

Investigators fitted the chamber over a square aluminum base supported several centimeters above the ground surface by hollow steel legs driven down to the permafrost. They created an airtight seal between the base and the chamber by lining adjoining surfaces with rubber gasket. They sealed the base to the tundra by weighting an attached plastic skirt with heavy chains. Where possible, they pushed the chains firmly down into the moss layer to create a good seal.

Investigators screwed the LiCor custom chamber head attachment over holes drilled into the plexiglass chamber, again sealing it with a rubber gasket. They mixed the air in the chamber using four small fans powered by a 12 V battery.

At each plot, investigators took measurements to create a light response curve. Two to three measurements were made at ambient light conditions, followed by 2 flux measurements at each of 2 successive shading levels with finally 3 measurements under complete darkness. They shaded the chamber by layering 3 fine mesh net cloths with tarpaulin to block all light from the chamber. Flux measurements under complete darkness represent ecosystem respiration. At each light level a flux measurement lasted 45 - 60 seconds in total. The LiCor recorded CO₂ and H₂O concentrations in the chamber every 2 - 3 seconds. After each measurement, investigators lifted the chamber until CO₂ and H₂O concentrations had stabilized at ambient levels.

After they created each light curve response, investigators measured a grid of 36 depth measurements from the top surface of the base to the ground to determine the chamber volume. They placed a 1 m x 1 m plastic frame with a 20 cm x 20 cm string grid on top of the base. They then added the volume of the space below the chamber base to the volume of the chamber itself and measured the surface area of the inside of the chamber to be 0.89 m³.

Investigators usually calculated NEP from the first 15 - 20 seconds of measurement. They used the entire period of 45 - 60 seconds where the data is scattered due to very small net changes in CO₂ over time. If light levels change during a measurement, investigators used only the periods where the light is constant to calculate the flux. Investigators often discarded the first few seconds of data (under shade or darkness) because the CO₂ concentration change over time is non-linear, representing adaptation of the system to new conditions.

Investigators usually calculated H₂O flux from the first 15 - 20 seconds of the measurement period. However, they calculated H₂O flux over the entire 60-second period where the CO₂ flux was calculated over the entire 60-second period. The build up of water vapor in the chamber almost always followed a curve, which began to plateau towards the end of 60 seconds.

Investigators measured NDVI on each flux plot using either a portable 2 channel field sensor (Skye Instruments) or Unispec spectral analyzer (PP Systems) or both:

• Toolik 2003: Skye sensor
• Toolik 2004: Unispec and Skye sensor
• Abisko 2004: Unispec and Skye sensor (Unispec only at STEPPS site, phase 2)
• Abisko & Svalbard 2005: Unispec and Skye sensor (Unispec only during June at Abisko)

The Unispec spectral analyzer measures reflected light intensity in 256 portions of the visible spectrum from approximately 300 nm to 1000 nm. A foreoptic cable transmits light from the target to the instrument; each measurement scan lasts for approximately 10 ms. Investigators measured 9 scans in a regular grid for each of the flux plots. They kept the end of the fiber optic 60 vertical centimeters above the ground surface, which resulted in a view of the vegetation that was approximately 20 cm in diameter. They measured the incident radiation using a reference standard so that the reflectance from the vegetation could be calculated as a percentage of incoming solar radiation. Investigators used the program Multispec5.1.5.exe to compile the Unispec reflectance spectra from the raw target spectra.

The Skye NDVI sensor measures total radiation reflected from the vegetation (without measuring incident radiation) in the wavebands 570 nm - 680 nm and 725 nm - 1000 nm. NDVI for both instruments is calculated as indicated in the Data Processing section. Investigators reported all times as local times. They did not record shade levels in 2003.

Processing (CO₂ flux measurements):

Fluxes are calculated from the slope of chamber CO₂ (µmol*mol^-1) [or H₂O mmol*mol^-1] concentration recorded by the LiCor against time.

NEP = (rho*vol*dC/dt)/SA rho = (P_av*1000)/(R*T) where
     NEP = net CO₂ flux (µmol m^-2*s^-1)
     rho = air density (mol/m³)
     vol = chamber volume (m³)
     dC/dt = slope of chamber CO² concentration against time (µmol*mol^-1*s^-1)
     SA = chamber surface area (m²) = 1
     P_av = pressure (kPa)
     R = ideal gas constant 8.314 (J*mol*K^-1)
     T = temperature (K)

RE = NEP_{measured under complete darkness}
GEP = RE - NEP
NDVI = (RII-RI)/(RI+RII) where
     RI = average light reflectance from 570 nm - 680 nm (µmol*m^-2*s^-1)
     RII = average light reflectance from 725 nm - 1000 nm (µmol*m^-2*s^-1)

Processing (Light response curve parameters):

Investigators fitted a saturating (Michaelis-Menton-type) function to the measured flux. They calculated the best-fit parameters describing each light curve by minimizing the sum of squared errors between measured and modeled NEP. The light response curve is modeled as follows:

NEP = Re - ((Pmax*max PAR)/(K+max PAR)) where
     Re = ecosystem respiration (µmol C*m^-2_ground*s^-1)
     Pmax = theoretical light saturation GPP (µmol C*m^-2_ground*s^-1)
     K = half saturation constant (µmol PAR*m^-2_ground*s^-1)
     max PAR = maximum ambient PAR at which a flux measurement was taken for the sunlight curve (µmol PAR*m^-2_ground*s^-1)

Investigators calculated initial slope of the light response curve (light use efficiency of E₀) and the light compensation point (LCP) from these parameters as follows:

E₀ = Pmax/K
LCP = (Re*K)/(Pmax-Re)

NDVI = (RII-RI)/(RI+RII) where
     RI = average light reflectance from 570 nm - 680 nm (µmol*m^-2*s^-1)
     RII = average light reflectance from 725 nm - 1000 nm (µmol*m^-2*s^-1)

Plot GPS locations and vegetation description

Percent plant cover by species

No cover data are available for flux plots at Imnavait Creek, Alaska in 2003.

Investigators estimated absolute aerial cover by species for all vascular plants in each flux plot (Total cover can be greater than 100%). They also noted bryophtye cover, bare ground, cryptigamic crust, rock, and standing water. In 2004, they split each flux plot into 25 sub plots using a grid, estimated the percent cover in each of the sub plots individually, and then calculated an average. In 2005, they used the same grid but counted running totals of percent cover in squares 1 through 25. Investigators reported the total cover for the flux plot.

Investigators assigned each species a six-letter code; the first three letters of the genus species name. SPP indicates that species is not known. Investigators reported the total for the growth form where many graminoids were growing together and it was not possible to judge the individual percentages. The main species present are listed in the COMMENTS column of the data file.

Percent plant cover by functional type

No cover data are available for flux plots at Imnavait Creek, Alaska in 2003.

Investigators estimated absolute aerial cover by species for all vascular plants in each flux plot (for example, total cover can be greater than 100%). They also noted bryophtye cover, bare ground, cryptogamic crust, rock, and standing water. In 2004, they split each flux plot into 25 sub plots using a grid and estimated percent cover in each of the sub plots individually, then calculated an average. In 2005, they used the same grid but counted running totals of percent cover in squares 1 through 25. (Investigators reported the total cover for the flux plot.)

Investigators assigned each species to a growth form.

D = Deciduous shrub
E = Evergreen shrub
F = Forb
G = Grass
GRM = Graminoid
S = Sedge/rush
P = Pteridophyte
B = Bryophyte (mosses and liverworts)
L = Lichen
U = Unclassified
W = Water
R = Rock
X = Litter, bare, or crust
++ = Plus other species

Processing:

Total vascular cover equals the sum of all deciduous, evergreen, forb, grass, sedge, graminoid, and pteridopyte cover:

TotVasc = D + E + F + G + P + S + GRM where
     TotVasc = total absolute vascular cover
     D = Deciduous shrub
     E = Evergreen shrub
     F = Forb
     G = Grass
     P = Pteridophyte
     S = Sedge/rush
     GRM = Graminoid

Investigators calculated the abundance of each growth form as a proportion of the total vascular cover (such as, for deciduous vegetation):

Vasc%Decid = (D/TotVasc)*100 where
     Vasc%Decid = % of total vascular cover that is deciduous
     TotVasc = total absolute vascular cover
     D = total deciduous cover

Point framing

Investigators collected point frame data on 8 flux plots along the topographic sequence of the west facing slope of Imnavait Creek (Alaska USA) catchments in 2003.

Investigators characterized each flux plot by point-intercept sampling. They used a 0.75 m x 0.75 m point frame with a 10 x 10 grid of sampling points. They dropped a 5 mm pin vertically through the vegetation at each of the 100 points and recorded total number of contacts made with any leaf material (equaling the number of LEAF HITS) after the pin was fully lowered.

Investigators assigned each species to a growth form.

D = Deciduous shrub
E = Evergreen shrub
F = Forb
G = Grass
GRM = Graminoid
S = Sedge/rush
P = Pteridophyte
B = Bryophyte (mosses and liverworts)
L = Lichen
U = Unclassified
W = Water
R = Rock
X = Litter, bare, or crust

5. References and Related Publications

Hooper, D. U., Z. G. Cardon, F. S. Chapin III, and M. Durant. 2002. Corrected calculations for soil and ecosystem measurements of CO₂ flux using the LI-COR 6200 portable photosynthesis system. Oecologia 132:1-11.

Williams, M., L. Street, M. T. Van Wijk, and G. R. Shaver (in press). Identifying differences in carbon exchange among arctic ecosystem types. Ecosystems.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document:

Document Creation Date

October 2006

Document URL

http://data.eol.ucar.edu/codiac/dss/id=106.ARCSS162