Harvard Forest

Data Archive

HF005

Prospect Hill Soil Warming Experiment at Harvard Forest since 1991

Related Publications

Data

• hf005-01: trace gas flux (preview)
• hf005-02: lysimeter (preview)
• hf005-03: nitrogen mineralization (preview)
• hf005-04: soil temperature (preview)
• hf005-05: soil respiration (preview)
• hf005-06: fine root biomass (preview)
• hf005-07: soil moisture (preview)
• hf005-08: soil warming layout

Overview

• Lead: Serita Frey, Jerry Melillo
• Investigators: Kristen DeAngelis, Melissa Knorr
• Contact: Information Manager
• Start date: 1991
• End date: 2021
• Status: ongoing
• Location: Prospect Hill Tract (Harvard Forest)
• Latitude: +42.54 degrees
• Longitude: -72.18 degrees
• Elevation: 365 meter
• Datum: WGS84
• Taxa:
• Release date: 2024
• Language: English
• EML file: knb-lter-hfr.5.37
• DOI: digital object identifier
• EDI: data package
• DataONE: data package
• Related links:
• Barre Woods Soil Warming Experiment at Harvard Forest since 2001
• Study type: long-term measurement
• Research topic: large experiments and permanent plot studies; soil carbon and nitrogen dynamics
• LTER core area: mineral cycling, disturbance patterns
• Keywords: carbon, carbon dioxide, climate change, methane, nitrogen, nitrogen mineralization, nitrous oxide, soil moisture, soil respiration, soil temperature, soil warming
• Abstract:

  The soil warming experiment was installed on the Prospect Hill tract in 1991 to allow us to investigate the effects of a 5 deg C temperature increase on soil processes fundamental to the global cycling of carbon and nitrogen. The experiment is located in an even-aged mixed hardwood forest. Six replicates of three treatments, Heated (resistance heating cables buried at 10cm and maintained at a 5 deg C differential from the control plots), Disturbance Control (cables installed but not powered) and Control treatments make up the randomized block design. The temperature differential is maintained with monitoring at five minute increments by an automated thermistor network in the plots, wired to a multiplexer and a datalogger in the control shed. In the plots, measurements of trace gasses (CO2, N2O and CH4), nitrogen mineralization, soil moisture and soil water chemistry have allowed us to quantify changes in the soil system.

  Ten years of elevated soil temperatures at the Harvard Forest soil warming experiment suggest that there are limits to a positive feedback to the global warming cycle. After many early years of increased CO2 fluxes from the warmed plots, years nine and ten have revealed no significant differences in releases of CO2 between the heated and control plots. Nitrogen mineralization has shown a large response to warming as well, with twice the rate of N mineralized in years 1-4, followed by a gradual decrease in rates to about the 40% level in 1998. Resumption of mineralization measurements in 2001 reveals a continued decrease in mineralization rates.

  Field results from the soil warming experiment indicate that only a small fraction of the soil carbon in this mid-latitude forest ecosystem will be lost to the atmosphere in response to warming. We find that a 5 deg C warming of the soil for a decade results in a loss of about 11% of the carbon stored in the top 60 cm of soil, with most of this loss occurring in the first four to five years. By the end of the decade, warming no longer stimulates soil carbon loss. In addition, we find that warming accelerates the soil nitrogen cycle, particularly in the early years of warming. This acceleration has the potential to stimulate plant carbon storage.

  Calculations based on nitrogen uptake in vegetation at the Chronic N Experiment (Magill, Aber et al. 2000) allow us to estimate how much additional carbon might be stored in plants as a result increased N availability at soil warming. Our calculations show that the potential increase in carbon stored is large enough to more than compensate for the soil carbon loss, so that warming may actually stimulate carbon storage at the ecosystem level in this mid-latitude forest.

  We are currently expanding our research from the original soil warming experiment to investigate this important feedback at the Harvard Forest. The existing 6x6m plots on the Prospect Hill tract are not large enough to allow for the study of treatment effects on trees, so we are installing a larger warming experiment. The new experiment will have two 30x30m plots, a heated and a control plot, in the Slab City Tract of the Harvard Forest. Many aspects of this experiment will be the same as the original. Using resistance heating cables and thermistors, we will maintain a 5 deg C differential between the heated and control plots, year-round. In addition to the trace gas, nitrogen mineralization and soil water parameters measured to date, we will also be measuring woody increment and other vegetation metrics to allow us to investigate the plant response to perturbations in the carbon and nitrogen cycles.

• Methods:

  Gas measurements were made by placing chamber lids over anchored collars for 15 min and sampling the headspace at 5-min intervals. Samples were analyzed for trace gas concentrations by gas chromatography or infrared analysis, and the changes in concentration were used to calculate net flux rates. On each sampling date, fluxes were measured at early morning and afternoon intervals. N2O and CH4 fluxes were measured from 1991 to 1995 along with the CO2 measurements using the same static chamber method.

  Soil temperatures were measured at the surface and 2 and 4cm at the time of each gas sampling. Plot temperatures were also constantly monitored by an automated thermistor system, allowing comparison between control and heated plots at 5 minute intervals, with according powering up or down of the plots as needed.

  Soil moisture measurements were conducted using gravimetric techniques for the first 4 years of the study and by time domain reflectometry (TDR) from 1995-2002.

  Net N mineralization and nitrification were measured for the forest floor and mineral soil using an on-site buried bag incubation. Incubations were for 6 weeks, April- November, and for 5 months through the winter. Initial samples were collected and analyzed for extractable (2N KCl, 48 hours) NH4+ and NO3- content. The same analysis was carried out on the incubated samples. The difference in total mineral N content between initial and incubated soils is the net mineralization rate.

  Concentrations of inorganic N in water leaching below the rooting zone were measured using high-tension lysimetry. Soil water samples were collected from one porous cup lysimeter per plot on two occasions every month for the first 2 years of the experiment, then monthly. Lysimeters were installed at a depth of 50 cm and evacuated to 15 in Hg 24 h before sampling. Samples were frozen until they were analyzed for NH4+ and NO3-.

• Organization: Harvard Forest. 324 North Main Street, Petersham, MA 01366, USA. Phone (978) 724-3302. Fax (978) 724-3595.

• Project: The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. (ROR).

• Funding: National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210.

• Use: This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.

• License: Creative Commons Zero v1.0 Universal (CC0-1.0)

• Citation: Frey S, Melillo J. 2024. Prospect Hill Soil Warming Experiment at Harvard Forest since 1991. Harvard Forest Data Archive: HF005 (v.37). Environmental Data Initiative: https://doi.org/10.6073/pasta/abf59a218a5868baf5b2c073a7dd1d7f.

Detailed Metadata

hf005-01: trace gas flux

1. year: year
2. rep: replicate number
3. date: sample date
4. treatment: treatment code
   • 1: control
   • 2: disturbed control
   • 3: heated 5 deg C
5. block: block number. There are 3 blocks, each with 6 plots grouped in a randomized block design.
6. co2_flux: CO2 flux (mg C/m2/hr). Samples collected every 5 min for 15 min using a static chamber method. Samples analyzed by infrared analysis (unit: milligramPerMeterSquaredPerHour / missing value: NA)
7. ch4_flux: CH4 flux (mg C/m2/hr). Samples collected every 5 min for 15 min using a static chamber method. Samples were analyzed by gas chromatography. (unit: milligramPerMeterSquaredPerHour / missing value: NA)
8. n2o_flux: N2O flux (ug N/m2/hr). Samples collected every 5 min for 15 min using a static chamber method. Samples were analyzed by gas chromatography. (unit: microgramPerMeterSquaredPerHour / missing value: NA)
9. temp_2cm: soil temperature at 2 cm depth taken at the time of gas sampling (unit: celsius / missing value: NA)
10. temp_4cm: soil temperature at 4 cm depth taken at the time of gas sampling (unit: celsius / missing value: NA)
11. grav_h2o_org: organic gravimetric soil water (g H2O/g soil) (unit: gramsPerGram / missing value: NA)
12. grav_h2o_min: mineral gravimetric soil water (g H2O/g soil) (unit: gramsPerGram / missing value: NA)
13. vol_h2o: soil water (cm3 H2O/cm3 soil) measured using time domain reflectometery (TDR) (unit: cubicCentimetersPerCubicCentimeters / missing value: NA)

hf005-02: lysimeter

1. date: sample date
2. year: year
3. plot: plot number
4. treatment: treatment code
   • C: control
   • DC: disturbed control
   • H: heated 5 deg C
5. lys_no3: samples were collected from a high-tension lysimeter installed at a depth of 50cm. Samples were analyzed for dissolved NO3- (unit: milligramsPerLiter / missing value: NA)
6. lys_nh4: samples were collected from a high-tension lysimeter installed at a depth of 50cm. Samples were analyzed for dissolved NH4+ (unit: milligramsPerLiter / missing value: NA)
7. volume: volume of sample collected (unit: milliliter / missing value: NA)
8. notes: notes

hf005-03: nitrogen mineralization

1. year: year
2. rep: replicate number
3. date: sample date
4. horizon: soil horizon
   • 0: organic
   • 3: mineral
5. treatment: treatment code
   • C: control
   • DC: disturbed control
   • H: heated 5 deg C
6. plot: plot number
7. net_no3: net N mineralization in the form of NO3- (mg N/kg) released during incubation period (unit: milligramPerKilogram / missing value: NA)
8. net_nh4: net N mineralization in the form of NH4+ (mg N/kg) released during incubation period (unit: milligramPerKilogram / missing value: NA)
9. net_ion: combined net mineralization (mg N/kg) released during incubation period (unit: milligramPerKilogram / missing value: NA)
10. days_incu: number of days of on-site buried bag incubation (unit: number / missing values: NA)
11. depth: depth of soil horizon (unit: centimeter / missing value: NA)
12. bd: bulk density greater than 2mm (unit: gramPerMeterCubed / missing value: NA)

hf005-04: soil temperature

1. date: date
2. year: year
3. doy: Julian date (unit: nominalDay / missing value: NA)
4. month: month
5. day: day
6. plot1h: temp measured at 5 cm depth in plot 1 (heated) (unit: celsius / missing value: NA)
7. plot6h: temp measured at 5 cm depth in plot 6 (heated) (unit: celsius / missing value: NA)
8. plot8h: temp measured at 5 cm depth in plot 8 (heated) (unit: celsius / missing value: NA)
9. plot12h: temp measured at 5 cm depth in plot 12 (heated) (unit: celsius / missing value: NA)
10. plot15h: temp measured at 5 cm depth in plot 15 (heated) (unit: celsius / missing value: NA)
11. plot16h: temp measured at 5 cm depth in plot 16 (heated) (unit: celsius / missing value: NA)
12. plot3d: temp measured at 5 cm depth in plot 3 (disturbance control) (unit: celsius / missing value: NA)
13. plot5d: temp measured at 5 cm depth in plot 5 (disturbance control) (unit: celsius / missing value: NA)
14. plot9d: temp measured at 5 cm depth in plot 9 (disturbance control) (unit: celsius / missing value: NA)
15. plot10d: temp measured at 5 cm depth in plot 10 (disturbance control) (unit: celsius / missing value: NA)
16. plot13d: temp measured at 5 cm depth in plot 13 (disturbance control) (unit: celsius / missing value: NA)
17. plot17d: temp measured at 5 cm depth in plot 17 (disturbance control) (unit: celsius / missing value: NA)
18. plot2c: temp measured at 5 cm depth in plot 2 (control) (unit: celsius / missing value: NA)
19. plot4c: temp measured at 5 cm depth in plot 4 (control) (unit: celsius / missing value: NA)
20. plot7c: temp measured at 5 cm depth in plot 7 (control) (unit: celsius / missing value: NA)
21. plot11c: temp measured at 5 cm depth in plot 11 (control) (unit: celsius / missing value: NA)
22. plot14c: temp measured at 5 cm depth in plot 14 (control) (unit: celsius / missing value: NA)
23. plot18c: temp measured at 5 cm depth in plot 18 (control) (unit: celsius / missing value: NA)
24. avg_heat: average temp in Heated plots (unit: celsius / missing value: NA)
25. avg_cont: average temp in Control plots (unit: celsius / missing value: NA)
26. avg_dcon: average temp in Disturbance Control plots (unit: celsius / missing value: NA)
27. shed_air: average air temp taken at the Prospect Hill Soil Warming site (unit: celsius / missing value: NA)

hf005-05: soil respiration

1. datetime: date and time
2. year: year that the data was collected
3. month: month that the data was collected
4. day: day the data was collected
5. time: time data was collected rounded to the nearest hour
6. treatment: treatment code
   • C: control
   • DC: disturbance control
   • H: heated plot
7. plot: Plot ID
8. co2_flux: CO2 flux in mg C m-2 h-1 (unit: milligramPerMeterSquaredPerHour / missing value: NA)
9. temp_4cm: soil temperature at 4 cm depth (unit: celsius / missing value: NA)
10. moisture: soil moisture (% volumetric moisture content) (unit: dimensionless / missing value: NA)
11. rainflag: whether or not sampling was likely affected by a respiration pulse from a recent (within 2 days) significant precipitation event
    • 0: not likely affected by rain pulse
    • 1: likely affected by rain pulse
12. measurement: measurement type
    • Li8100-a: automatic LI-COR measurement
    • static: static chamber gas syringe measurement

hf005-06: fine root biomass

1. date: sample date
2. plot: plot number
3. treatment: treatment code
   • DC: disturbed control
   • H: heated
4. horizon: soil horizon
   • M: mineral
   • O: organic
5. sorter: technician who sorted roots into live and dead pools
   • 1: technician 1
   • 2: technician 2
   • 1,2: both techician 1 and technician 2 worked on this sample
6. live_dead: whether live or dead roots
   • Live: live roots
   • Dead: dead roots
7. size_class: root diameter size class (mm)
8. biomass: root biomass (unit: gramsPerSquareMeter / missing value: NA)
9. n_per: percent nitrogen content of bulked roots of this class, expressed as a decimal (unit: dimensionless / missing value: NA)
10. c_per: percent carbon content of bulked roots of this class, expressed as a decimal (unit: dimensionless / missing value: NA)
11. d15n: nitrogen isotope ratio content of bulked roots of this class, expressed as d15N (o/oo vs. AIR) (unit: dimensionless / missing value: NA)
12. d13c: carbon isotope ratio of bulked roots of this class, expressed as d13C (o/oo vs. PDB) (unit: dimensionless / missing value: NA)

hf005-07: soil moisture

1. date: date
2. p1_sm: TDR volumetric soil moisture in Plot 1 (Heated) (unit: dimensionless / missing value: NA)
3. p2_sm: TDR volumetric soil moisture in Plot 2 (Control) (unit: dimensionless / missing value: NA)
4. p3_sm: TDR volumetric soil moisture in Plot 3 (Disturbance Control) (unit: dimensionless / missing value: NA)
5. p4_sm: TDR volumetric soil moisture in Plot 4 (Control) (unit: dimensionless / missing value: NA)
6. p5_sm: TDR volumetric soil moisture in Plot 5 (Disturbance Control) (unit: dimensionless / missing value: NA)
7. p6_sm: TDR volumetric soil moisture in Plot 6 (Heated) (unit: dimensionless / missing value: NA)
8. p7_sm: TDR volumetric soil moisture in Plot 7 (Control) (unit: dimensionless / missing value: NA)
9. p8_sm: TDR volumetric soil moisture in Plot 8 (Heated) (unit: dimensionless / missing value: NA)
10. p9_sm: TDR volumetric soil moisture in Plot 9 (Disturbance Control) (unit: dimensionless / missing value: NA)
11. p10_sm: TDR volumetric soil moisture in Plot 10 (Disturbance Control) (unit: dimensionless / missing value: NA)
12. p11_sm: TDR volumetric soil moisture in Plot 11 (Control) (unit: dimensionless / missing value: NA)
13. p12_sm: TDR volumetric soil moisture in Plot 12 (Heated) (unit: dimensionless / missing value: NA)
14. p13_sm: TDR volumetric soil moisture in Plot 13 (Disturbance Control) (unit: dimensionless / missing value: NA)
15. p14_sm: TDR volumetric soil moisture in Plot 14 (Control) (unit: dimensionless / missing value: NA)
16. p15_sm: TDR volumetric soil moisture in Plot 15 (Heated) (unit: dimensionless / missing value: NA)
17. p16_sm: TDR volumetric soil moisture in Plot 16 (Heated) (unit: dimensionless / missing value: NA)
18. p17_sm: TDR volumetric soil moisture in Plot 17 (Disturbance Control) (unit: dimensionless / missing value: NA)
19. p18_sm: TDR volumetric soil moisture in Plot 18 (Control) (unit: dimensionless / missing value: NA)

hf005-08: soil warming layout

• Compression: none
• Format: gif
• Type: image