Throwback Thursday: Studying Wood Density

The density of a tree significantly affects the properties of wood products. Density is determined by a number of factors, including wood species, growth condition (such as type of soil, available water, and sunlight) and competition from other trees and plants.

This image of two southern pine logs below shows the drastic effect growth conditions can have on wood density. Although both were of the same species, the tree on the left grew slowly and has high density, whereas the tree on the right grew quickly and has low density.


The density of a tree can be determined before it’s cut down using an increment borer to sample the wood in the tree. This photo from the 1960s show’s Forest Service employee Richard Nielsen taking a sample with an increment borer.


Here’s what the increment borer wood sample looks like: CORENote the annual growth rings. By counting the rings, the age of the tree can be determined; measuring the space between the rings can estimate the rate of growth. The density can also be estimated by weighing the sample and knowing its volume.

A western wood density survey was conducted in the 1960s by FPL along with industry and university partners. Some timber was commercially inaccessible, such as this sample of Englemann spruce, which had to be packed out of the forest on horseback.

135387-6Back at the Lab, the researchers got to work. Here, Dimitri Pronin and Arnie Okkonen weigh disks of wood to determine specific gravity.


Throwback Thursday: 65 Years, 77 Degrees Difference

It doesn’t take a scientist to tell you that it’s been an unseasonably warm winter in the Midwest. Sometimes, all you need is a photographer.


View from the top of the FPL January 30, 2015. The temperature reached 40 degrees that day.


The same view from the top of the FPL January 30, 1951. The temperature plunged to -37 degrees that day.

True to tradition, Forest Products Laboratory (FPL) photographer Stephen Schmieding, ascended to the top of the laboratory Saturday to capture this striking image of a warming Wisconsin. Comparing the 40 degree weather to the -37 degree bone-chilling temperatures of winters past is a striking reminder of the roller-coaster weather our nation has, and will continue to experience.

Throwback Thursday: Statistics Program Transcends Decades

The following blog is from the book Forest Products Laboratory 1910-2010, Celebrating A Century of Accomplishments.

This major study, preformed in the 1980s, is referred to as the “in-grade testing of structural lumber program,” and is one of the largest cooperative research programs ever undertaken by the North American wood engineering community.

It included universities, the Southern Pine Inspection Bureau, the West Coast Lumber Inspection Bureau, the Western Wood Products Association, a number of companies, and the Forest Products Laboratory (FPL).

Failure of a piece of structural lumber that was subjected to bending forces to help determine allowable design properties for structural lumber.


Physical and mechanical properties information was obtained on 33 species or species groups of visually graded structural lumber. Over an eight-year period, nearly 70,000 pieces of lumber — approximately 1,000,000 board feet — were tested to destruction in bending, tension, or compression.

The information provided the basis for more accurately estimating mechanical properties of lumber and revising allowable design properties.

Thanks to FPLs statistical design for selecting the wood samples, testing them, and analyzing the outcomes, the results from the study were useful and applicable to structural lumber in general. The data garnered from this research is now part of the National Design Standard, and is still used today.

Throwback Thursday : Pine Posts Preserved Despite Surrounding Soil

An aerial view of FPL from the 1970s with its signature light posts clearly visible.

Recently, the Forest Products Laboratory (FPL) said goodbye to several hard-working members of a team that has posted silent guard over the parking lots since the late 1960s.


A light post awaits removal and replacement in front of FPL.

The distinctively curved, brown, wood-laminated, light posts were unceremoniously removed from FPL’s parking lots amid fears of waning structural integrity. For nearly five decades, these lights have greeted employees and visitors, but have lost the battle of time to the relentless forces of wind, water, and heat — at least above ground.

Though flaking paint and rusting metal fasteners may be what these sentinels are remembered for, below ground, they remained remarkably well preserved.

They will soon be replaced with newer, safer, metal counterparts — and although they no longer stand at FPL, they will forever stand as examples of the incredible durability and longevity of wood products.

Beneath the ground, the light posts remained in remarkable condition.

Throwback Thursday : FPL Helps to Catch a Crimson Criminal

The following is an excerpt from Forest Products Laboratory 1910 – 2010 : Celebrating a Century of Accomplishments.

Wood science is not always about designing ingenious experiments or cutting-edge inventions. Over the years, researchers at the Forest Products Laboratory (FPL) have been called upon to use their expertise to help other agencies. Sometimes, this amounts to nothing more than uncovering decayed trees in a local city park, but in this case, it meant helping to convict a killer on the other side of the country.

In the “Case of the Red Paint Chip,” a murder had taken place in Georgia. The victim was found in the woods covered with debris, including chairs, rugs, cushions and two red painted posts. This area was used by hunters, who apparently brought the items and left them there.

The red posts, however, were thought to belong to the suspect, the husband of the victim. The victim’s son confirmed that red posts were stored in the house and that he had seen them in his father’s pickup truck.

In the victims house, under the stairs where the red posts had been stored, a red paint chip was found on a piece of yellow pine. This red paint was compared with the red paint on the posts, and a good match was noted in gross structure and chemical analysis. The forensic scientist in charge noted that there were a few fibers clinging to the back of the red paint chips.

Regis Miller, from the Center for Wood Anatomy Research at FPL, was asked to examine these fibers to determine whether they were conifer fibers from the yellow pine lumber, or fibers from the red painted posts, which were identified as from a species in the white oak group.

Sample and magnified view of the paint chip found on a pine board in the basement of the accused murderer’s home.

The ray cells did not have any cross-field pitting and no ray tracheids were evident, suggesting that they were hardwood ray cells and not rays from a conifer. These fibers were of two types: pointed thick-wall fibers and long, broad, thin-walled fibers. Fibers of two distinct types do not occur in the conifers, but they do occur in some hardwoods.

Miller concluded that the fibers were libriform fibers and vasicentric trachids that are typical of oak. Under high magnification and polarized light, the fibers from the red paint chip appeared to have large slit-like structures that initially were thought to be pits. Upon closer scrutiny, however, these slit-like structures were found to be the openings caused by decay fungi.

This decay pattern was found both in the fibers clinging to the red paint chip and the white oak posts. Not only were the decay patterns the same, they came from the same type of fungus. This case used both identification and comparative anatomy to show that the red paint chip found in the house did come from the red painted posts found at the scene of the crime.

Miller concluded that the, “analysis of the fibers attached to the paint chip indicated that the paint was from some hardwood posts that were found with the victim’s body and had been stored in the basement of the accused murderers home, and not from the pine 2×4. The paint was evidently chipped off when the posts were moved from the basement and used to help cover the victim’s body.”