Biomass Sampling Protocol
for Broadleaved Deciduous Species

FIA Study Plan

Draft 1 - 06182012

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Sample Tree Selection

Species selectionis based on ranks of growing stock volume in eastern or western regions. Species identified for southeastern United States for the 2012 field season include red maple (Acer rubrum L.) and white oak (Quercus alba L.). Additional species and species groups will be selected in subsequent years to comprise 70% of growing stock.

Site selection in the 2012 field season should take into consideration opportunities for working in sites, stands, and tracts where accessibility and proximity to laboratory facilities are favorable. We hypothesize that differences in ecological and edaphic factors will have significant relationships with aboveground tree biomass and carbon content; however, the focus in year 1 is the development and testing of procedures that will be most efficacious in quantifying the nature of these relationships over a broad geographical extent.

Tree selectionshould account for the widest range of ecological and edaphic factors possible, given the opportunities available for selecting sites in year 1. At minimum, trees selected should span one order of magnitude in dbh, e.g., spanning a range from 3 to 30 inches, and uniformly cover the range of dbh with gaps generally no larger than 2" in the sample range. Trees should be selected from as many as possible of five canopy position categories for forest-grown trees - open-grown, dominant, codominant, intermediate, and suppressed - recognizing that it may not be possible to sample all tree sizes in all canopy positions. To the extent possible, when more than one tree is selected in any 2" diameter class, variation in their heights and crown architectures - numbers, sizes, and heights of branches - should be as large as possible. While trees exhibiting defects such as hollow stems, broken tops or branches, poor form, etc., can be selected, the majority of sample trees should be relatively free from major defects of this type.

Measurements of Stand and Site Attributes

The geographic coordinates of each sample tree should be collected using a GPS receiver accurate, nominally, to within ± 10 feet. Where possible, GPS coordinates should be corrected using DGPS to achieve accuracy within ± 5 feet.

A circular plot of radius 24 feet, centered on the subject tree pith, shall be used to determine the numbers, sizes (dbh and height), and species of all neighboring trees ≥ 4" dbh. Where several subject trees will be selected for measurement in close proximity to each other, it may be advantageous to construct a stem map extending out 24' from any of the subject trees.

Timing of Measurements

Foliage biomass can only be measured in deciduous broadleaved trees during the summer growing season when foliage is fully displayed; however, when foliage biomass observations are not needed, considerable effort can be saved by making observations during the dormant season.

Growing season measurements should be made following the complete expansion of the initial (spring) flushes of leaves in red maple and white oak, and before the onset of late season (autumn) senescence. Completeness of leaf expansion can be observed directly, or approximated by allowing 4-6 weeks to pass after bud burst. Senescence can be determined based on late-season foliage colors.

Dormant season measurements should be made following autumn leaf drop, and prior to spring bud burst.

Standing Tree Measurements

Standing tree measurements are necessarily limited by the tools and time available to conduct observations without sacrificing the sample tree. Translation of standing tree protocols tested here to an operational procedure is expected; therefore, measurements deemed excessively detailed or inappropriate for operational use will not be considered. Exceptions will be made in the 2012 field season to allow for the development and testing of novel methods or tools.

Tree. The following tree attributes should be recorded for trees to be included in the standing-tree measurements database for the 2012 field season:

Main Stem. The main stem is generally defined as the largest-diameter branch at a fork or node that ultimately leads to an apical control point (Cost 1978). If it is not clear which branch to consider as the main stem based on diameter and position, then the selection that extends to the highest point will be chosen. When neither distinction can be made, the branch on the observer's right, or one chosen through a flip of a coin should be classified as the main stem.

The following attributes of the main stem should be recorded for trees to be included in the standing-tree measurements database for the 2012 field season:

Branches. (First order) branches are those that originate along the main stem and are at least 0.5" in diameter at their origin. The following attributes of first-order branches should be recorded.

Felled Tree Measurements

Following completion of the standing tree measurements, the tree will be felled at or below the 0.5" stump height. A Humboldt notch is preferred, when possible, to preserve the bole section above the stump height. Once the tree is safely on the ground, the following measurements will be made.

Tree. The taped total height of the tree, including the 0.5" stump height.

Main Stem.

The following attributes of the main stem should be recorded based on taped heights, where the taped heights are aligned with the standing tree measures, e.g., stump height breast height, 8', 12' etc.

Branches. The following attributes of first-order branches should be recorded.

Dissected Tree Fresh Measurements

Stem Sections.

Stem sections are numbered consecutively with integers starting with the first section cut above the stump. Marking each section number on the cut surface, large end, is helpful for avoiding mix-ups during subsequent handling and processing. Other than section 1, heights of the small ends (tops) of each section should correspond to tape-measured heights of (section #) × (4 feet). The following measurements should be recorded from each stem section.

Note: coloration due to heartwood is not considered a defect

Stem Disks.

One or more disks (1" to 3" thickness) should be cut from each stem section for the purpose of determining dry-to-green weight ratios and basic density measurements. When saw-kerf loss measurements by weight are desired, a convenient method is to make three saw cuts near the stem-section midpoint, about 2" apart. The three cuts produce two disks, which should be labeled with the section number and letters A and B.

Unitless dry-to-green weight ratios determined from disks will be used to estimate stem-section dry weights without having to oven-dry entire sections. Collection of disk specimens at regular intervals up the stem allow for determination of any systematic variation in moisture content or basic density with stem height. Collection of two or more disks in a single section allow for additional characterization of variance in moisture content or basic density within sections.

The following green measurements should be recorded from each disk as soon as possible after felling. Disks not immediately available for measurement should be stored in sealed plastic bags or containers and kept cool to avoid moisture loss, shrinkage, or molding.

Note: U.S. standard units (0.1 inches, 0.1lb) may be used, but effort should be made to maintain 3 significant digits in disk measurements.

Fresh Bark Measurements (optional).

Fresh bark measurements provide a means to develop estimators for green bark weight and volume, along with inside bark green weight and volume. On sample disks selected for fresh bark measurements, bark should be carefully removed as soon as possible after felling and the following additional disk measurements should be recorded:

Note: U.S. standard units (0.1 in, 0.05 lb) may be used, but effort should be made to maintain 3 significant digits in disk and bark measurements.

Kerf Weight (optional).

Kerf weight losses can be important to account for biomass lost during the dissection of stems and large branches. Saw kerf weight loss can be measured in the field by subtracting stem weight sections before and after cutting disks, and dividing by the number of cuts made ( Figure 1 ). Due to the relatively low resolution of affordable field scales, it is recommended that multiple saw cuts be made for each difference calculation. A convenient method is to make three saw cuts through the stem near the section midpoint, about 2" apart, producing two disks. The following weight measures and calculations are then made.

Branches - Leafless (dormant season).

The green (field) weight of each first-order branch should be measured in the field and recorded alongside the branch number. It may be necessary to section branches to fit them into the scale apparatus or weigh in stages, then sum the weights. When removing branches from the main stem, chainsaw cuts should be made that generally preserve the stem form ( Figure 1 ). The whole branch weight to be measured is

Following weighing, small branches may be clipped using shears or loppers and placed in labeled paper bags or boxes for subsequent transportation and drying. Large branches may be further processed by subsampling (see Optional Subsampling next section).

Optional Subsampling. For large branches, some subsampling of the branch material may be required to reduce the amount of material to be transported and dried. The subsample weight to be measured is

Following weighing, the subsample should be clipped using shears, loppers, or saws and placed in labeled paper bags or boxes for subsequent transportation and drying.

Branches with Leaves (growing season).

Separation of leaves from branches is generally not practical in the field; therefore, the processing of branches during the growing season should be done in steps to provide a way to distinguish between dry weights of branch foliage and wood components. The field procedure below, listed as a sequence of steps, provides a means to accomplish this goal.

The partial (leafless) branch weight (step D) to be measured in the field is

Following weighing, the partial (leafless) branches may be clipped using shears or loppers and placed in labeled paper bags or boxes for subsequent transportation and drying. Large partial branches may be further processed by subsampling (see Optional Subsampling next section).

Optional Subsampling. For large partial (leafless) branches, some subsampling of the branch material may be required to reduce the amount of material to be transported and dried. The subsample weight to be measured is

Following weighing, the subsample should be clipped using shears, loppers, or saws and placed in labeled paper bags or boxes for subsequent transportation and drying.

Green Foliage Weights (optional).

Measurements of green foliage weights followed by subsequent drying and reweighing, provide a means to estimate the green weight of foliage by branch or whole tree. Since it's generally impractical to separate all the leaves from a branch while fresh, a subsample of leaves should be collected from each branch selected for green foliage weight measurement, recording:

Dry weight measurements should be recorded in the same units and same decimal precision as green weights were recorded, whether in the field (branches, branch subsamples) or laboratory (disks, bark). Drying oven temperatures should be set between 100° - 105° C. Oven-dry condition of specimens should be by verified by noting that no appreciable weight change occurs over a 24 hr period. A separate document, Equilibrium Moisture Content in Wood Specimens, describes a procedure for adjusting weights of specimens dried at oven temperatures lower than 100°C.

Twig and foliage specimens (see section Branches with Leaves) from each branch are oven-dried and sorted to separate the leaf & twig components ( Figure 4 ). Twig dry weights must be attributed to the corresponding branch they were excised from to properly determine the dry weight of wood & bark of each branch. Foliage dry weights are also attributed to the corresponding branches they were excised from. In cases where subsamples of foliage were (optionally) weighed green (see section Green Foliage Weights), their weights must be recorded in the subsample database, then also attributed to the total foliage dry weight for the branch from which they were taken.

Bark Measurements.

Two biomass attributes that require the measurement of bark are I.) the dry weight contents of bark, e.g., as a fraction of total tree weight, or as a fraction of the weight of a cross-section cut from a stem or branch, and II.) the volumetric contents of bark in relation to outside-versus-inside-bark green volumes of stems or branches. While both I. and II. require separating bark from wood, weight determinations are flexible to allow separation of bark from wood either before or after specimens are oven-dried. Volumetric measurements should be made prior to drying to avoid irreversible dimensional changes. In cases where separating bark from disk specimens while fresh is not feasible, partial information can be obtained by separating bark from disks after drying.

Bark weight.

Bark weight determination as a fraction of stem cross-section can be made conveniently on disk sections after their ovendry weights have been recorded. Using a chisel or other sharp instrument, bark should be removed from the disk specimen. It may be necessary to bag and re-dry the separated bark to oven-dry condition again before re-weighing. Several measurements required for determining bark fraction of a disk are identical to the standard the disk measurement protocol (see section Stem Disks). In addition, bark dry weight should be recorded.

Pairing bark dry weight with disk dimensional and dry weight measurements ensures that bark-weight:disk-weight ratios can be computed for sample disks of any diameter. Further, the dry weight of bark per unit of green disk volume can be computed for sample disks or sections of wood of varying diameters.

Optional Detailed Stem and Branch Measurements.

Randomized branch sampling (RBS) and importance sampling (IS) from whole-tree taper models are candidate procedures for estimating whole tree and component biomass without separating and weighing tissues from whole trees. The following optional measurements can aid in assessing the precision of either method. In addition, since whole-tree taper models are seldom available ( e.g., Van Deusen and Roesch, 2011 ), detailed measurements from felled trees can be collected here for that purpose.

A meaningful numbering system for RBS segments branches assigns integers 1, 2, 3 etc. to segments that originate from a single node. For consistency, the integer digits are assigned in descending order of the segment diameter, i.e. the largest stem or branch at a node is numbered 1 and the next largest branch is numbered 2, etc., but this ordering is not strictly necessary. Following the RBS layout, the main stem below the first node is numbered as segment 1. Its dimensions and green weight are measured from the stump to the cut points immediately above the first node ( Figure 2, cut points d and e). The digit 1 is preserved to serve as the ID of the node from which the next two segments originated. They are distinguished from one another by a new digit (either 1 or 2) appended to their originating node ID. At each node encountered, a new digit is appended to the path ID accumulated to that point. The ID of a terminal segment includes identifying information for all the segments followed as a path is traversed from base to tip. For example, the terminal segment 1121 (Figure 2 ) followed a path through stem segments 1 and 11, branch segment 112, and finally branch segment 1121.

Measurements to be made for each segment include

An additional pair of measurements to collect from each stem or branch segment includes the segment diameter immediately below its upper node, along with the length along the segment from its base to the measurement point. These measurements can be used to parameterize whole-tree taper models that represent accumulated cross-sectional area of stem and branch material at specified distances from the stump. In Figure 2, the optional segment length (between cut point "g" and the point immediately below the upper node) of segment ID 111 is labeled, along with the point of measurement for its diameter.

Additional measurements of branch segment diameters at specified distances along segments may optionally be collected. Presumably, any additional measurement pairs would be collected on relatively long (e.g., > 2 ft) branch or stem segments.