We’ve all hiked in the woods or seen a fallen tree in a park and looked at its rings. One common bit of knowledge passed on to us since we were kids was that if we count that tree’s rings we’ll know its age. Had an infomercial announcer been on-hand, he’d have said, “But wait! There’s more.”
Five Sections of a Tree
Pith. The pith, at the center of the tree, is the original stem.
Heartwood. The heartwood is the older, inactive, non-functioning wood at the center of the tree, surrounding the pith. Heartwood is darker and denser than sapwood.
Sapwood. The outer four to 20 rings of the tree are sapwood. The sapwood of a tree is living material, and it’s light in color.
Cambrium. Between the bark and wood is the cambrium layer. This layer is responsible for a tree’s growing diameter. It also is the layer than responds to external damage by developing callus tissue to repair, for examples, cuts into the tree.
Bark. The outer most layer of the tree is bark. It protects the tree from the environment. The outer layer of bark is dead, while the live inner layer of bark transports nutrients throughout the tree.
Image of tree anatomy from NWFA University's “Basic Tree Anatomy” online course for professionals.
Growth Rings | Purpose + Wood Floor Character
The annual rings of a tree are composed of large pores that carry water up to the leaves. Each annual ring acts as a vertical cylinder. Medullary ray cells run perpendicular to the annual rings, carrying sap and delivering nutrients to the inner layers of the tree.
If you look at a tree stump or a cut end of a tree, you’ll see medullary rays, or pith rays, as light-colored ribbons seeming to radiate out from the center of the tree. These lines create some of the visual appeal you see in quarter-sawn wood floors. The quarter-sawn wood cut exposes the rays as added character in a floor.
Early Wood and Late Wood
Early wood, or spring wood, is formed in the spring each year. Late wood, or autumn wood, forms during the winter. It’s denser and occurs when the tree goes into seasonal dormancy.
Late wood creates darker graining in wood flooring. Light and dark variations in the grain of a wood floor show the seasonal patterns of early and late wood.
Softwood and Hardwood
Softwoods come from conifers. Those are needle-bearing trees which remain green throughout the year. Examples of softwood trees are pine, spruce, Douglas fir, and cedar.
Hardwoods come from deciduous, broad-leafed trees. Hardwood trees lose their leaves annually. Examples of hardwood trees are oak, maple, ash and cherry.
But here’s the catch: Whether a tree is softwood or hardwood does not refer to density. A softwood tree can provide harder material than a hardwood tree.
Janka hardness information from the National Wood Flooring Association's technical manual.
Most Common Tree Species in North America
Wood flooring produced from trees grown in North America most commonly are of these seven species.
Oak. There are many subspecies of oak, but the most commonly grown and used in North America are red oak and white oak. Red oak has a pinkish to red-brown color and has a more open grain pattern. White oak has a light-brown appearance and has longer, more noticeable rays in its grain.
Red and white oak trees take 40 years to reach cut-ready maturity. But oak trees in the U.S. typically are not cut until they reach 60 years of age. This creates a surplus inventory that protects the forest.
Maple. There are nearly 150 subspecies of maple. Maple light-colored wood with a closed-grain pattern. It’s a common wood used in residential flooring and gym floors.
Hickory. There is wider color variation in hickory, from tan to reddish to cream color. Hickory has a much more open and irregular grain pattern. Bonus fact: Hickory’s strength has made it a choice species for the handles of striking tools (e.g. hammers, axes).
Cherry. This species has a light to dark red- brown color. It appears with a fine, uniform grain that makes it useful for wood flooring, furniture and musical instruments.
Walnut. The color of walnut is much darker, from dark brown to purplish black. Walnut shows a straight open-grain pattern that also can have burled, curly character.
Ash. Colors of ash range from tan to dark brown. Ash tends to have bold, straight, moderately open grain with occasionally wavy figuring. Bonus fact: Beyond wood flooring, ash is commonly used to make baseball bats, rowing oars, and pool cues.
Pine. Antique hard pine and Southern yellow pine are used for flooring. The antique pine is darker and has denser grain. Southern yellow has a closed grain with a high level of character, including knots.
Use the search bar at the top of this web page to find wood flooring by species.
After a Tree Is Cut
Wood shrinks. Wood expands. It’s natural and ongoing, even after the tree is cut. The difference is “water weight,” so to speak.
The absorption and release of moisture content from wood flooring differs depending on how the wood was cut. As moisture increases, the floor boards swell and expand width-wise. And vice-versa as moisture is lost in a drier environment.
How much wood flooring expands and shrinks, how reactive it is to changes to temperature and humidity in its environment, is referred to as stability. The higher the degree of stability in a wood floor, the less it reacts to those environmental changes by shrinking or expanding.
Lumber mills and flooring manufacturers use air- and kiln-drying processes to reduce the moisture content of wood to ready it for use. The moisture content of wood flooring needs to reach and be maintained at a certain level before and after it is installed. The level of moisture content a floor needs
depends on the environment where it is located.
We talk about the effect of geographic location, humidity and temperature on hardwood floors in our “Acclimation for Wood Flooring” and “Humidity Matters” posts on this blog. What’s needed for wood flooring success in Colorado is different than in the wet Pacific Northwest or highly humid Florida.
Trees, Wood Flooring + Environmental Sustainability
Most domestic wood flooring comes from trees harvested in the Eastern half of the United States. The U.S. Department of Agriculture counts more trees in North America now than in the 1950s, with 730 million acres of forest in the U.S.
The Eastern hardwood forests are being professionally managed, and grow more trees than the number being harvested. Limitations are set for harvesting from old-growth and endangered-species forests.
Because of the longevity of hardwood as a flooring material, which can last for more than 100 years in a home when maintained, wood flooring is considered an environmentally responsible choice for flooring. To learn more about how to make the most of your wood floors, check out our Ultimate Guide to Hardwood Flooring.
Palo Duro Hardwoods is the region’s leading expert on all things wood flooring. Subscribe to Palo Duro’s monthly email newsletter to get free knowledge for use on the job or in your home.
Have questions? Call Palo Duro’s sales team at 303-375-0280.