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Harvard Forest Data Archive


Nonstructural Carbohydrates in Defoliated Oaks in Central Massachusetts 2019-2020

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  • Lead: Audrey Barker Plotkin, Meghan Blumstein
  • Investigators: Danelle Laflower, Greta VanScoy
  • Contact: Information Manager
  • Start date: 2018
  • End date: 2020
  • Status: completed
  • Location: Central Massachusetts
  • Latitude: +42.3144 to +42.5313
  • Longitude: -72.5308 to -72.1676
  • Elevation: 60 to 300 meter
  • Taxa: Lymantria dispar (gypsy moth), Quercus alba (white oak), Quercus rubra (red oak)
  • Release date: 2021
  • Revisions:
  • EML file: knb-lter-hfr.369.2
  • DOI: digital object identifier
  • EDI: data package
  • DataONE: data package
  • Related links:
  • Study type: short-term measurement
  • Research topic: invasive plants, pests and pathogens; physiological ecology, population dynamics and species interactions
  • LTER core area: organic matter, disturbance
  • Keywords: carbohydrates, defoliation, disturbance, invasive species, mortality, oak, tree physiology
  • Abstract:

    Carbon starvation posits that defoliation- and drought-induced mortality results from drawing down stored nonstructural carbohydrates (NSCs), but evidence is mixed and mortality is often observed prior to full drawdown of NSCs. We tested the relationship between defoliation severity, NSC drawdown, and tree mortality by measuring NSCs in mature oak trees defoliated by gypsy moths across a natural experimental gradient of defoliation severity. We collected stem and root samples from oaks (Quercus rubra and Q. alba) in interior forests (n=34) and forest edges (n=47) in central Massachusetts, USA. Total NSC (TNC; sugar + starch) stores were analyzed with respect to tree size, species, and defoliation severity, which ranged between 5 and 100%. Forest edge trees had higher TNC stores that were less sensitive to defoliation than interior forest trees. However, TNC stores declined significantly in both groups with increasingly severe defoliation. Furthermore, we observed a mortality threshold of 1.5% dry weight TNC. Our study draws a direct link between insect defoliation and TNC reserves and defines a TNC threshold below which mortality is highly likely. These findings advance understanding and improve model parametrization of tree response to insect outbreaks, an increasing threat with globalization and climate change.

  • Methods:

    Study sites and sample selection

    During the mid-late growing season of 2018, we established two study sites. We established plots in the Quabbin Watershed Forest (‘Forest’). Plots had varying defoliation severity, as classified by a published Landsat timeseries analysis (Pasquarella, V.J., Bradley, B.A, and Woodcock, C.E. 2017 Near-real-time monitoring of insect defoliation using Landsat time series. Forests 8(8), 275; doi:10.3390/f8080275.). Within plots, defoliation of oaks also varied. That is, even in lightly defoliated areas we observed a few oaks that were severely defoliated. We also tagged 85 individual oak trees from roadsides and hedgerows in and within 15 km of the mid-sized town of Amherst, Massachusetts (‘Town’). For each tree, we recorded diameter at breast height (DBH), species, and canopy position (1 = full sun; 2 = partially shaded; 3 = mostly/fully shaded). In the Forest plots, we recorded defoliation class (1 = 0-25% defoliated; 2 = 25-50% defoliated; 3 = 50-75% defoliated; 4 = 75-100% defoliated). For the Town trees, we estimated defoliation to the nearest 5%. These two sites were established independently and came together in Winter 2018-2019 for this study.

    From these sites, we selected 34 Forest trees (from four plots) and 47 Town trees for NSC sampling, representing a range of defoliation severity in 2018. Note: we did not use the data collected from Quabbin Plot 6, because these trees likely died prior to autumn 2018, nor did we use the ‘Harvard Forest’ site in our analyses. All selected trees were alive in late summer 2018, although some were predicted to die within a year based on a visual assessment of crown dieback. Secondary selection criteria included sampling a range of tree size and species. Diameter of the sample trees ranged from 15-69 cm at the Forest site (mean 49 cm) and from 12-66 cm at the Town site (mean 35 cm). Most of the oaks at the two sites were red oak (Quercus rubra L., n = 66) but we included white oak (Q. alba L., n = 15) to the extent it was available.

    NSC sampling

    We sampled NSCs in February 2019, and again in February 2020. From each sample tree, we collected a 2 cm (under bark) sample of wood from: 1) the stem, at ~1.3 m height; and 2) a coarse root, at ~20 cm from the base of the tree. Samples were collected using a standard 4.3 mm diameter increment borer, stored on ice in the field, and then stored in a −80o C freezer until processing.

    Tree defoliation, dieback, and mortality assessments

    We assessed defoliation and/or dieback four times over the course of the study. At the initial defoliation assessment in late summer 2018, some of the Forest trees exhibited branch dieback and browning leaves. We recorded crown dieback and mortality status at leaf-out in May 2019, during June – August 2019 and in July – August 2020. A tree was presumed dead if it did not produce leaves; no tree that failed to leaf out in May 2019 produced leaves later that season or in 2020. Crown dieback was rated visually on a five-point scale (1 = 0-25 dieback; 2 = 25-50% dieback; 3 = 50-75% dieback; 4 = 75-99% dieback; 5 = dead). In 2019, we recorded defoliation by gypsy moths during their larval period from late May – early July. Despite high egg-mass counts in Fall 2018, high larval mortality in 2019 led to very low defoliation (Brown, 2019). There were few gypsy moth larvae and minimal defoliation in 2020.

    NSC analysis

    Total NSC reserves were extracted from freeze-dried and ground woody tissue samples following the protocol of Landhäusser et al. (Landhäusser SM, Chow PS, Dickman LT, Furze ME, Kuhlman I, Schmid S, Wiesenbauer J, Wild B, Gleixner G, Hartmann H, et al. 2018. Standardized protocols and procedures can precisely and accurately quantify non-structural carbohydrates. Tree physiology 38: 1764–1778.). In brief, after grinding the wood samples using a Wiley mill and then a ball grinder, we extracted sugars from 30 mg of dried tissue using 80% hot ethanol, then read them using a phenolic colorimetric assay and a spectrophotometer at 490 nm (ThermoFisher Scientific Genesys 180 UV-Vis Spectrophotometer). The methodology extracted and quantified all soluble sugars in the samples, including glucose, sucrose, fructose, and other oligosaccharides and glucans. We included two internal laboratory standards (Q. rubra stem-wood) with each set of samples, with sets within 10% of the laboratory estimate (42 mg g-1) accepted.

    Starch was extracted from the tissue remaining after sugar extraction. We solubilized the tissue in NaOH, then incubated it with alpha-amylase and amyloglucosidase digestive enzymes, which digest starch into glucose. Solutions were assayed using a PGO-color reagent solution (Sigma Chemicals) and read on the spectrophotometer at 525 nm. Starch concentrations of mg glucose-starch-equivalent per g dry wood were calculated based on a glucose standard curve (Sigma Chemicals).

  • 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.

  • Citation:

    Barker Plotkin A, Blumstein M. 2021. Nonstructural Carbohydrates in Defoliated Oaks in Central Massachusetts 2019-2020. Harvard Forest Data Archive: HF369 (v.2). Environmental Data Initiative:

Detailed Metadata

hf369-01: trees

  1. site: site
    • Amherst: Town
    • Harvard Forest: Simes
    • Quabbin: Forest
  2. plot: plot name
  3. tree: tree number. Unique identifier is combination of plot and tree
  4. tag: tag number for Quabbin plot trees that are part of related permanent plot study
  5. point: one of 3 variable-radius plot centers established in 2018 in the Quabbin plots
  6. species: species
    • Q. alba: white oak
    • Q. rubra: northern red oak
  7. diameter at breast height (unit: centimeter / missing value: NA)
  8. can.exp: canopy exposure
    • 1: full sun
    • 2: partially shaded
    • 3: mostly/fully shaded
  9. ref.class.18: defoliation class in 2018. Based on def.per.18 for the Amherst trees
    • 1: 0-25% defoliated
    • 2: 25-50% defoliated
    • 3: 50-75% defoliated
    • 4: 75-100% defoliated
  10. def.per.18: percent defoliation in 2018; to nearest 5% for Amherst and mid-point of ref.class.18 for Quabbin (unit: dimensionless / missing value: NA)
  11. n.egg.masses.18: number of gypsy moth egg masses counted in summer-fall 2018; 30 means more than 30 and 100 means WAY more than 30 (unit: number / missing value: NA)
  12. cond.19: condition
    • D: dead
    • L: live in 2019
  13. defol.2019: defoliation class in 2019
    • 1: 0-25% defoliated
    • 2: 25-50% defoliated
    • 5: dead
  14. dieback.2019: dieback classes
    • 1: 0-25% dieback
    • 2: 25-50% dieback
    • 3: 50-75% dieback
    • 4: 75-99% dieback
    • 5: dead
  15. notes.18: notes about the tree in 2018
  16. notes.19: notes about the tree in 2019
  17. ind_leaf_defoliation_S19: average herbivory percent based on a sample of 30 individual leaves from that tree; summer 2019; Amherst trees only (unit: dimensionless / missing value: NA)
  18. defoliation_canopy_pct_F19: estimated percent defoliation; Amherst trees (unit: dimensionless / missing value: NA)
  19. ind_leaf_defoliation_F19: average herbivory percent based on a sample of 30 individual leaves from that tree; fall 2019; Amherst trees only (unit: dimensionless / missing value: NA)
  20. new_eggmasses_below2m_19: number of new gypsy moth egg masses counted in fall 2019 below 2 m on the tree (unit: dimensionless / missing value: NA)
  21. cond.20: condition in 2020
    • D: dead
    • L: live
  22. dieback.20: percent dieback in 2020
    • 1: 0-25% dieback
    • 2: 25-50% dieback
    • 3: 50-75% dieback
    • 4: 75-99% dieback
    • 5: dead
  23. note.20: notes about the tree in 2020

hf369-02: nonstructural carbohydrates

  1. identifier for sample vial
  2. site: site
    • Amherst: Town
    • Quabbin: Forest
    • Simes: Harvard Forest
  3. plot: plot name
  4. tree_id: unique identifier is combination of plot and tree
  5. tissue: root or stem
    • root: root
    • stem: stem
  6. sample weight (unit: milligram / missing value: NA)
  7. sugar.perc.dw: sugars in percent dry weight (unit: dimensionless / missing value: NA)
  8. starch.perc.dw: starch in percent dry weight (unit: dimensionless / missing value: NA)
  9. tnc.perc.dw: total nonstructural carbohydrates (sugars and starches) in percent dry weight (unit: dimensionless / missing value: NA)
  10. date: date that the sample was collected in the field
  11. month: month that the sample was collected in the field
  12. year: year that the sample was collected in the field
  13. note: note about the sample