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# Harvard Forest Data Archive

### HF125

## Coarse Woody Debris in Hemlock Removal Experiment at Harvard Forest since 2005

Related Publications### Data

- hf125-01: coarse woody debris (preview)
- hf125-02: fine woody debris (preview)
- hf125-03: snags and stumps (preview)
- hf125-04: figure and tables referenced in methods

### Overview

**Lead:**Aaron Ellison, Audrey Barker Plotkin**Investigators:**David Foster, David Orwig**Contact:**Audrey Barker Plotkin**Start date:**2005**End date:**2017**Status:**ongoing**Location:**Simes Tract (Harvard Forest)**Latitude:**+42.47 to +42.48**Longitude:**-72.22 to -72.21**Elevation:**200 to 240 meter**Taxa:***Tsuga canadensis*(eastern hemlock)**Release date:**2018**Revisions:****EML file:**knb-lter-hfr.125.19**DOI:**digital object identifier**Related links:**- Understory Vegetation in Hemlock Removal Experiment at Harvard Forest since 2003
- Overstory Vegetation in Hemlock Removal Experiment at Harvard Forest since 2003
**Study type:**long-term measurement**Research topic:**large experiments and permanent plot studies**LTER core area:**organic matter, disturbance**Keywords:**coarse woody debris, hemlock, hemlock woolly adelgid, timber harvest, vegetation dynamics**Abstract:**The woody detritus survey is designed to measure coarse woody detritus that includes snags, logs, and stumps, and to estimate fine woody detritus which includes smaller pieces of downed wood. To capture both standing and downed wood, we based our survey around two main types of methods, the line intercept method and the fixed radius plot method. Surveys have been completed for 2005, 2007, 2009, 2011, 2013, 2015 and 2017.

**Methods:**Details of our wood detritus survey methods are described below. Please see HF125-04 for associated figure and tables.

*The Line-Intercept Method for Downed Wood*Within each of the eight 90m x 90m plots of the manipulation we laid out eight transects (Figure 1). As each of the line-transects converges in the central 30m x 30m plot we left a 5m x 5m square space in the center of the plot to define a boundary to keep each of the transects separate. Coarse Woody Detritus (CWD, wood pieces greater than 7.5cm in diameter) is measured along the entire transect length, and Fine Woody Detritus (FWD, wood 7.5cm-0.6cm in diameter) is measured along 2m a subsection of each transect.

A. Coarse Woody Debris (CWD): the diameter, species (or species group) and decay class (Table 1) of each downed piece of wood that intersects the line-transect is measured using a 50cm caliper. When possible, two diameter measurements are taken, to account for the fact that most stems are not uniformly round. Location within 10-m section of the transect is also recorded. From there we can calculate volume per unit area by using the formula V = 9.869 * (d/8L), where L is length and d is diameter squared (Harmon and Sexton 1996).

Calculation Details:

1. Average the diameters using equation 2 from Harmon and Sexton (1996), which is a modified formula for an ellipse: Round Diameter = SQRT (Diameter1 * Diameter2).

2. Use equation 7 from Harmon and Sexton (1996) to first determine the volume: V = 9.869 * Sum of (d^22/8L), where V is volume (m3/m2), d is round diameter divided by 100 (to give diameter in meters), and L is transect length (m).

3. To convert volume into mass, use published densities by species and decay class reported in Lui et. al (2006) (wood density, g/cm3), a study that was done nearby (Table 2).

B. Fine Woody Debris (FWD): FWD is tallied along a randomly selected 2m section of each transect. Downed wood that intersects the line-transect is tallied within two size classes: 0.6-2.5cm and 2.5-7.5 cm (Harmon and Sexton 1996). These size classes originally were used in fuel loading surveys. Species and decay class is not recorded for these size classes. From there we can calculate volume by converting size class to volume using size class averages of a particular diameter and secants of incidence angle (Harmon and Sexton 1996). We then use the equation V = 9.869 * N * a (d/8L), where V is volume per unit area, d is the quadratic mean piece diameter for a size class, and a is the average secant piece along the transect (Harmon and Sexton 1996).

Calculation Details:

1. Overall, the goal was to solve for volume and mass, using equation 8 in Harmon and Sexton (1996) and site-specific density values to then convert volume to mass: V = 9.869 * N * a * (dq2/(8L), where V is volume (m3/m2), N is the tally of pieces of a size class along a sampled transect – field collection, a is the average secant of the pieces (from published values for Tsuga canadensis for plots 1-6 or Acer/Betula/Tilia for plots 7 and 8, given in Table 3 of Harmon and Sexton 1996), Dq is quadratic mean piece diameter for the given size class (m) (based on field collection: see below), and L is the transect length (m) sampled. To determine the term Dq, and site-specific density, we sampled FWD from the plots in July 2005:

2. In the buffer area of each plot at the Simes Tract, samples of each FWD size class (size class 1 is 0.6-2.5cm diameter and size class 2 is 2.51-7.5cm diameter) were haphazardly (as opposed to randomly or systematically) collected in the field. Samples from plots 1-6 (hemlock-dominated) were combined (n=24 for each size class) and samples from plots 7 and 8 were combined (n=20 for each size class).

3. Diameter of each sampled piece was recorded. The averaged sum of squared diameters, multiplied by 0.0001 to convert cm2 to m2, gives the term dq2 for the volume equation.

4. Next, the volume of each FWD sample was measured by water displacement.

5. Then, the FWD samples were oven dried and mass measured to 0.01 g.

6. Find density (g/cm3) for each piece by dividing mass into volume. Now, average the pieces from each size class and forest type (plots 1-6 vs. plots 7 and 8) to get 4 average density values to use.

7. Using these density values, mass of FWD can be calculated by multiplying density(g/cm3) * (1cm3/0.000001m3) * volume (m3/m2) to get mass as g/m2.

Note: in 2013, we decided to use fine woody debris density values for T. Canadensis (plots 1-6) or Acer/Betula/Tilia (plots 7 and 8) published in Harmon and Sexton (1996) rather than these density values, so we re-calculated fwd mass for all years. We continue to use the locally derived dq2 values (Table 3).

*Strip Plots to Measure Snags and Stumps:*To account for standing dead wood, we sample snags and stumps along a 4m-wide strip plot that straddles the line transect. Species (or species group) and decay class (Table 2) is recorded for each individual. To find the volume for snags and stumps we use the formula for the frustum of a cone which requires that we estimate the diameter of the wood at the top and measure the diameter of the wood at the bottom, as well as estimate its height. Getting these measurements for snags can become complex depending on the type of snag. For short snags and stumps, a 50cm caliper is used to measure top and bottom diameters, and a meter stick is used to measure height. For intact trees and tall snags, top diameter is visually estimated, and height is measured with a clinometer. For intact trees, top diameter is estimated as 1.0cm. Bottom diameter is measured with 50cm caliper. From these measurements we calculate volume as a frustum of a cone (Harmon and Sexton 1996). For some stumps with little taper, only one diameter was recorded, and volume was calculated as a cylinder rather than a frustrum of a cone.

Calculation Details:

1. If there are two measurements available, average the diameters of the top and the bottom measurements using equation 2 from Harmon and Sexton (1996): Round Diameter = SQRT (Diameter1 * Diameter2).

2. Find the area of the top and the bottom measurements using the formula for area of a circle.

3. To calculate height (cm) from clinometer measurements: (top-bottom)* distance.

4. Calculate volume as a fustrum of a cone – equation 4 from Harmon and Sexton (1996): V = L (Ab + (( Ab At )^0.5) + At)/3, where L is length (i.e. height) and A and A are the diameters at the base and the top.

5. To convert volume to mass, use the density values from Lui et. al (2006) Table 3 and multiply the densities by the volumes to find mass.

6. Find mass per unit area by dividing the mass by the length of the transect multiplied by 4.

7. Sum the masses of each transect to get mass per unit area.

8. For hollows use the same step 5 to find the volume and then subtract that volume from the original volume.

In 2005, mass of 33 intact trees was estimated using published allometric equations with diameter at breast height as the only input. See below for a list of equations used. In 2015, we re-calculated volumes of these 33 trees using the frustrum of a cone formula, assigning the top diameter = 1, and the dbh measurement as the bottom diameter. The mass of these 33 trees is still based on the allometric equations.

*Long-term Tagged Subset*To understand how the woody detritus is changing over time we tagged all dead wood within one randomly chosen strip plot of each of the eight plots.

*Hollow Wood and Elliptical Wood*Some special cases can arise where varying measurements will need to be made. When a piece of wood is hollow on the inside we will need to subtract out the volume of the hollows. This will be done by noting the exterior diameter of the piece of wood and the diameter and length of the hollow (Harmon and Sexton 1996). For pieces of wood that have an elliptical shape we will measure the maximum and minimum diameters and convert this to a round equivalent diameter using a version of the formula for the area of a ellipse, where A = SQRT(diam1*diam2).

*References*Harmon, M.E. and J. Sexton. 1996. Guidelines for measurements of woody detritus in forest ecosystems. Not a formal publication.

Liu, W.H., D.M. Bryant, L.R. Hutyra, S.R. Saleska, E. Hammond-Pyle, D. Curran and S.C. Wofsy. 2006. Woody debris contribution to the carbon budget of selectively logged and maturing mid-latitude forests. Oecologia 148:108-117.

Van Wagner, C.E. 1968. The line intersect method in forest fuel sampling. Forest Science 14:20-26.

*Allometric Equations*Allometric equations used to estimate mass of intact dead trees in the 2005 survey. Used for only 33 stems, total. All equations come from the published compilation (L.M. Tritton and J.W. Hornbeck 1982. Biomass equations for major tree species of the Northeast. USDA Forest Service Northeastern Forest Experiment Station Gen. Tech. Report NE-69).

Birch sp. Mass in pounds = EXP(0.4792+2.6634*LN(dbh inches)). Young et al. 1980; Range: 1-20in.; n=51.

Hemlock (or conifer). Mass in pounds =EXP(0.6803+2.3617*LN(dbh inches)). Young et al. 1980; Range 1-20in; n=36.

Maple. Mass in pounds =0.07592*((dbhinches^2)*(htcm/328))^1.0316. Wiant et al. 1979; Range 2-16in; n=19-22.

Oak. Mass in pounds =1.68914*(dbhinches^2.65978). Wiant et al. 1977; Range 2-16in; n=19-22.

Pine. Mass in pounds =EXP(0.408+2.449*LN(dbh inches)). Young et al. 1980; Range 1-26in; n=35.

**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:**Ellison A, Barker Plotkin A. 2018. Coarse Woody Debris in Hemlock Removal Experiment at Harvard Forest since 2005. Harvard Forest Data Archive: HF125.

### Detailed Metadata

**hf125-01: coarse woody debris**

- year: year
- plot: plot number (1-8)
- tran: transect number (1-8). Plot 7 excludes transects 2, 3, and 4 from 2011 onward. Analyses should account for having only 5 transects in this plot for these years.
- loc: area along transect, in 10m increments
- 1: 0-10m
- 2: 10-20m
- 3: 20-30m
- 4: 30-40m (OR 30-35 for P1T1, P2T5, P2T7, P3T3)
- 5: 40-50m

- num: sequence sample number, not # in field; just to keep spreadsheet in order; integers except hollows which are integer.1
- tlength: transect length (unit: meter / missing value: NA)
- diam1: diameter 1. Field measurement, measured with calipers. (unit: centimeter / missing value: NA)
- diam2: diameter 2. Field measurement. Measured perpendicular to diameter 1, if possible (e.g.; not possible if wood is sunk in ground) (unit: centimeter / missing value: NA)
- diamavg: quadratic mean diameter. SQRT(diam1*diam2) (unit: centimeter / missing value: NA)
- decaycl: decay class (1-5). See methods. (unit: number / missing value: NA)
- species: genus or major group
- volumem3m2: volume, formula: 9.869*((diamavg/100)^2) /(8*transect length) (unit: meterCubedPerMeterSquared / missing value: NA)
- densitygcm3: density by species and decay class; see methods; from Liu et al. (2006) (unit: gramsPerCubicCentimeter / missing value: NA)
- massgm2: mass, formula: density*volume*1000 (unit: gramsPerSquareMeter / missing value: NA)
- notes: notes

**hf125-02: fine woody debris**

- year: year
- plot: plot number (1-8)
- tran: transect number (1-8). Plot 7 excludes transects 2, 3, and 4 from 2011 onward. Analyses should account for having only 5 transects in this plot for these years.
- count.cl1: number of pieces in size class 1 (0.6-2.5cm diameter) along the 2m of the transect sampled (unit: number / missing value: NA)
- count.cl2: number of pieces in size class 2 (2.5-7.5cm diameter) along the 2m of the transect sampled (unit: number / missing value: NA)
- loc: start and end point (in m) of the fine woody debris subsample along the transect
- length.m: length of transect sampled (2m in all cases for this data set) (unit: meter / missing value: NA)
- a.cl1: average secant (a) for correcting orientation bias used in planar or linear intercept methods (from Table 3; Harmon and Sexton 1996); size class 1 (unit: dimensionless / missing value: NA)
- dq2.m2.cl1: squared average quadratic mean diameter for size class 1, m2 (based on sample of FWD collected from this study in 2005) (unit: squareMeter / missing value: NA)
- dens.gcm3.cl1: bulk density by species/species group for size class 1 (from Table 3; Harmon and Sexton 1996) (unit: gramsPerCubicCentimeter / missing value: NA)
- a.cl2: average secant (a) for correcting orientation bias used in planar or linear intercept methods (from Table 3; Harmon and Sexton 1996); size class 2 (unit: dimensionless / missing value: NA)
- dq2.m2.cl2: squared average quadratic mean diameter for size class 2, m2 (based on sample of FWD collected from this study in 2005) (unit: squareMeter / missing value: NA)
- dens.gcm3.cl2: bulk density by species/species group for size class 2 (from Table 3; Harmon and Sexton 1996) (unit: gramsPerCubicCentimeter / missing value: NA)
- vol.cl1.m3m2: volume of FWD in size class 1. V= 9.869 * N * a * (dq2/(8L) See Methods (unit: meterCubedPerMeterSquared / missing value: NA)
- vol.cl2.m3m2: volume of FWD in size class 2. V= 9.869 * N * a * (dq2/(8L) See Methods (unit: meterCubedPerMeterSquared / missing value: NA)
- mass.cl1.gm2: mass of FWD in size class 1. Vol.cl1.m3m2 * dens.gcm3.cl1/0.000001 (unit: gramsPerSquareMeter / missing value: NA)
- mass.cl2.gm2: mass of FWD in size class 2. Vol.cl2.m3m2 * dens.gcm3.cl2/0.000001 (unit: gramsPerSquareMeter / missing value: NA)

**hf125-03: snags and stumps**

- year: year
- plot: plot number (1-8)
- tran: transect number (1-8). Plot 7 excludes transects 2, 3, and 4 from 2011 onward. Analyses should account for having only 5 transects in this plot for these years.
- loc: area along transect in 10m increments
- 1: 0-10m
- 2: 10-20m
- 3: 20-30m
- 4: 30-40m (OR 30-35 for P1T1, P2T5, P2T7, P3T3)
- 5: 40-50m

- num: sequence sample number, not # in field; just to keep spreadsheet in order; integers except hollows which are integer.1
- tlength: transect length (unit: meter / missing value: NA)
- dbh: diameter at breast height used in allometric biomass equations for intact trees in 2005 only (unit: centimeter / missing value: NA)
- dtop1: top diameter1, measured with calipers or estimated visually if beyond reach (unit: centimeter / missing value: NA)
- dtop2: top diameter 2, measured perpendicular to first diameter, if possible (unit: centimeter / missing value: NA)
- dtopavg: diameter average, formula: SQRT(diam1*diam2) (unit: centimeter / missing value: NA)
- dbot1: bottom diameter 1, measured with calipers (unit: centimeter / missing value: NA)
- dbot2: bottom diameter 2, measured perpendicular to first diameter, if possible (e.g.; not possible if wood is sunk in ground) (unit: centimeter / missing value: NA)
- dbotavg: diameter average, formula: SQRT(diam1*diam2) (unit: centimeter / missing value: NA)
- clindist: distance to tree used to calculate height with clinometer (unit: meter / missing value: NA)
- clinbot: bottom clinometer reading, percent scale, used to calculate height with clinometer (unit: dimensionless / missing value: NA)
- clintop: top clinometer reading, percent scale, used to calculate height with clinometer (unit: dimensionless / missing value: NA)
- clinht: snag/stump height, formula: tree height= clindist*(clintop-clinbot) (unit: centimeter / missing value: NA)
- height: snag/stump height, copied from clinht or measured directly with tape in field (unit: centimeter / missing value: NA)
- type: category of dead wood
- snag: broken dead tree
- stump: cut tree
- hollow: within a snag/stump
- standing piece: vertical dead piece of wood, but not rooted in ground

- decaycl: decay class
- 1: solid wood, recently fallen, bark and twigs present
- 2: solid wood, significant weathering, branches present
- 3: wood not solid, bark may be sloughing but nail still must be pounded into wood
- 4: wood sloughing and/or friable, nail may be forcibly pushed into wood
- 5: wood friable, barely holding shape, nail may be easily pushed into wood

- species: genus or major group
- method: calculation method for volume/mass
- 1: frustrum of cone
- 3b: cylinder, using dbotavg as the diameter input
- 4: volume as frustrum of cone using dbh for diameter1 and 1cm for diameter2; mass calculated using a species-specific allometry (used only for 33 intact dead trees in 2005)

- volm3m2: dead wood volume (unit: meterCubedPerMeterSquared / missing value: NA)
- densitygcm3: density by species and decay class; see methods; from Liu et al. (2006) (unit: centimeterCubed / missing value: NA)
- massgm2: mass, formula: volumem3m2 * densitygcm3 (unit: gramsPerSquareMeter / missing value: NA)
- notes: notes

**hf125-04: figure and tables referenced in methods**

**Compression:**none**Format:**PDF**Type:**PDF