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Harvard Forest Data Archive

HF179

Inorganic Nitrogen Pools and Tree Composition in Hemlock Removal Experiment at Harvard Forest 2007-2009

Related Publications

Data

Overview

  • Lead: Tara Sackett, Nathan Sanders, Aimee Classen, Aaron Ellison
  • Investigators:
  • Contact: Tara Sackett
  • Start date: 2007
  • End date: 2009
  • Status: completed
  • Location: Simes Tract (Harvard Forest)
  • Latitude: +42.47
  • Longitude: -72.22
  • Elevation: 200 to 240 meter
  • Taxa:
  • Release date: 2011
  • Revisions:
  • EML file: knb-lter-hfr.179.6
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement
  • Research topic: invasive plants, pests and pathogens; soil carbon and nitrogen dynamics
  • LTER core area: inorganic nutrients
  • Keywords: ammonium, hemlock, hemlock woolly adelgid, leaf litter, nitrate, nitrogen
  • Abstract:

    This study assessed how the change in leaf litter input and environmental conditions, from that of hemlock stands to earlier successional deciduous stands, will affect inorganic nitrogen availability at the interface of the mineral soil and LFH horizons. In early October 2007 we exchanged 0.5 x 0.5 m "loaves" of LFH horizons from hemlock and deciduous stands between forest types, while keeping control plots in the original forest stands. Inorganic nitrogen outputs from the litter loaves were monitored for 20 months using ion-exchange resins, removing and replacing the resins three times at 5 - 8 month intervals. Results indicated that there were differences between the control hemlock and deciduous loaves - NO3 and NH4 availability were higher in deciduous stands. However, the transfer of litter loaves from one stand type to another did not reveal changes in nutrient availability due to a shift in habitat. Rather, the methodology of moving litter loaves to a new site caused greater changes in nutrient availability, particularly over the summer months.

  • Methods:

    Field Study

    1. Study sites: At each of two sites (A and B) in the Simes Tract of Harvard Forest (see map) we located a deciduous and hemlock forest stand. At site A, the hemlock and deciduous stands were within 100 m of each other. At site B the stands were within 600 m of each other.

    2. Plot selection: Within each stand we selected 18 0.5 x 0.5 m plots (total 72 plots). We chose plots haphazardly, but with the following restrictions: (a) Must only be underneath hemlock canopy in H stands, and underneath deciduous canopy in D stands. (b) Within a stand, must be separated at least 7-10 m. (c) Flat(tish) (d) Without small trees or shrubs (e) No visible rocks or tree roots.

    3. Treatments: We used reciprocal switching of the LFH horizons in 0.5 x 0.5 m plots from deciduous and hemlock stands to investigate how a shift in litter inputs and environments would influence inorganic nitrogen availability. There were six treatments, each with 3 replicate in each site (n=6 total): (1) Deciduous to deciduous switch (DD-swi), (2) Deciduous to hemlock switch (DH-swi), (3) Hemlock to hemlock switch (HH-swi), (4) Hemlock to deciduous switch (HD-swi), (5) Hemlock control (no switch) (HH-con), (6) Deciduous control (no switch) (DD-con).

    4. Plots: We cut the LFH "litter loaves" as follows: I measured out plots (0.5 m x 0.5 m) with a quadrant, made initial cut with a bread knife, and then final cuts with a flat-edged spade. Small roots were cut with a saw. Rocks were left behind because they were usually big. We cut down to above the mineral layer of soil, and so the loaf consisted mainly of LFH horizons, although some A horizon was included. Loaves were a mean of 12.6 plus or minus 0.3 (SE) cm (n=48) in height. Loaves were lifted out of the ground and placed on an aluminum sheet, on top of a square of plywood. We measured the height of the soil and litter layer on each of the four sides of the loaves, and the height at the centre of the loaf (to the nearest cm) (Table 1). A 4-sided "cookie cutter" of aluminum flashing was placed around the litter loaf so it wouldn’t fall apart or lose litter while being moved around. Undisturbed controls were flagged but not cut. Litter loaves were switched haphazardly (we only made sure that adjacent plots weren’t ending up near each other) within or between forest types within each site. No across site switches were made. We carried the loaves on the plywood to the plot where they would be placed. The aluminum flashing cookie cutter was taken off the loaf, it was lifted off the plywood, still on top of the aluminum sheet, and placed in the hole. We then slid out the aluminum sheet, settled the loaf into the ground, and flagged each corner of the plot.

    5. Plot loss: In site A, a HH-con and HD-swi plot were lost as the following spring it turned out they had been placed in spot where there is a shallow vernal pool.

    6. Measurement of inorganic N in soil solutions: Ion-exchange resin bags were made by using rubber tubing to form a ring with a surface area of 64 cm2, placing the rubber ring in the toe of an (unenforced) nylon stocking, and measuring out 15 mL of ion-exchange resin (MTO-Dowex MR-3 LCNG) into the nylon bag. Bags were tied off securely. One resin bag was inserted below each litter loaf on 1 November, 2007. Resin bags were removed and new ones inserted on 22 May 2008, 1 Oct 2008, and 4 July 2009. At the time of collection 1, resin bags had disappeared or been damaged from 4 plots; at the time of collections 2 and 3 from 2 plots. These data are missing from the dataset.

    7. Soil samples: In July 2009 humus samples were taken from the bottom of the litter loaf (~ 20g) for inorganic N measurements. At this point the flags were removed from the plots. An inadequate quantity of soil was taken from 3 plots, these data are missing from the dataset.

    Laboratory Analysis

    Resins: To determine NO3 and NH4 adsorbed to the resin surface, resins were dried, and then extracted with 100 mL of 2M KCl. Upon addition of KCl, bottles were shaken manually, and then placed on an orbital shaker for an additional 45 minutes. Extracts were filtered through #1 Whatman filters and frozen until analysis. NO3 and NH4 concentrations were determined colourimetrically on a Lachat flow injection analyzer (Lachat Instruments, Milwaukee, WI, USA).

    Soils: To determine extractable NO3 and NH4 concentrations from the humic fractions, ~ 10 g (fresh weight) of soil was extracted with 100 mL of 2M KCl. Samples were shaken with KCl for 1 hour, allowed to settle overnight (refrigerated), and filtered through Whatman #2 filter paper. NO3 and NH4 concentrations were determined as for resin extracts.

  • Use:

    This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.

  • Citation:

    Sackett T, Sanders N, Classen A, Ellison A. 2011. Inorganic Nitrogen Pools and Tree Composition in Hemlock Removal Experiment at Harvard Forest 2007-2009. Harvard Forest Data Archive: HF179.

Detailed Metadata

hf179-01: treatment and sample information

  1. plot: number assigned to each sample plot for analyses
  2. site: site
    • A: site A
    • B: site B
  3. origin: habitat where litter loaf was removed from
    • H: hemlock
    • D: deciduous
  4. destination: habitat where litter loaf was inserted
    • H: hemlock
    • D: deciduous
  5. sample: description of field plot of origin and destination. C = control; H=hemlock; D=deciduous.
  6. disturbance: whether litter loaves were switched or remained in place (disturbance control)
    • switch: litter loaves were switched
    • control: litter loaves remained in place (disturbance control)
  7. treatment: code describing each of the six treatments
    • DD_swi: deciduous to deciduous switch
    • DH_swi: deciduous to hemlock switch
    • HH_swi: hemlock to hemlock switch
    • HD_swi: hemlock to hemlock switch
    • HH_con: hemlock control (no switch)
    • DD_con: deciduous control (no switch)

hf179-02: resin data

  1. collection: collection
    • 1: 1st resin bag installation and collection period
    • 2: 2nd resin bag installation and collection period
    • 3: 3rd resin bag installation and collection period
  2. plot: sample plot code
  3. site: site
    • A: site A
    • B: site B
  4. treatment: code describing each of the six treatments
    • DD_swi: deciduous to deciduous switch
    • DH_swi: deciduous to hemlock switch
    • HH_swi: hemlock to hemlock switch
    • HD_swi: hemlock to hemlock switch
    • HH_con: hemlock control (no switch)
    • DD_con: deciduous control (no switch)
  5. date.install: date resin bag buried
  6. date.remove: date resin bag retrieved
  7. days: number of days resin bags were buried (unit: number / missing value: NA)
  8. no3: NO2/NO3 measured by Lachat (unit: milligramsPerLiter / missing value: NA)
  9. nh4: NH4 measured by Lachat (unit: milligramsPerLiter / missing value: NA)
  10. no3.blank: Lachat measurement of blank for NO2/NO3 (unit: milligramsPerLiter / missing value: NA)
  11. nh4.blank: Lachat measurement of blank for NH4 (unit: milligramsPerLiter / missing value: NA)
  12. volume: volume of KCl used to extract resin (unit: liter / missing value: NA)
  13. no3.day: NO2/NO3 standardized as μg /day adsorbed by resin (unit: microgramPerDay / missing value: NA)
  14. nh4.day: NH4 standardized as μg /day adsorbed by resin (unit: microgramPerDay / missing value: NA)

hf179-03: soil data

  1. plot: sample plot code
  2. site: site
    • A: site A
    • B: site B
  3. treatment: code describing each of the six treatments
    • DD_swi: deciduous to deciduous switch
    • DH_swi: deciduous to hemlock switch
    • HH_swi: hemlock to hemlock switch
    • HD_swi: hemlock to hemlock switch
    • HH_con: hemlock control (no switch)
    • DD_con: deciduous control (no switch)
  4. no3: NO2/NO3 measured by Lachat (unit: milligramsPerLiter / missing value: NA)
  5. nh4: NH4 measured by Lachat (unit: milligramsPerLiter / missing value: NA)
  6. no3.blank: Lachat measurement of blank for NO2/NO3 (unit: milligramsPerLiter / missing value: NA)
  7. nh4.blank: Lachat measurement of blank for NH4 (unit: milligramsPerLiter / missing value: NA)
  8. volume: volume of KCl used to extract soil (unit: liter / missing value: NA)
  9. mass.soil: dry weight soil extracted (unit: gram / missing value: NA)
  10. no3.soil: μg NO2/NO3 per g dry weight soil (unit: microgramsPerGram / missing value: NA)
  11. nh4.soil: μg NH4 per g dry weight soil (unit: microgramsPerGram / missing value: NA)

hf179-04: hemlock litter loaf map

  • Compression:
  • Format: jpg
  • Type: jpg