The Importance of a Tree's Butt

The Base of a Tree is Also Called It's Butt

cypress butt swell
Cypress-gum Swamp. Steve Nix

The butt of a tree is it's bottom portion and this basal portion of the trunk is distinctively different from a tree's branches, roots, and upper trunk.  A tree's "butt" is above the roots but separated from the trunk which continues upward toward the terminal bud

A tree's butt is often referred to by loggers as the bottom log of a felled tree. The first cut nearly always starts at the butt or base of the tree for the initial cut.

It is the most valuable part of the tree when sold and converted to a wood product

A tree butt is also important when tree disease is detected at or near ground level. Butt rot diseases are serious concerns for tree owners and tree managers. A basal rot will inevitably weaken the tree to the point where its support system is compromised resulting in trunk failure and the eventual death of the tree.

The butt of a tree is also its most valuable section to a timber grower. If there is a defect in the butt log which by definition is the first 16 feet of a tree trunk, the tree's lumber grade is diminished considerably.

Butt Rot and Effects on Trees

Butt rot is a serious disease of trees and all species are susceptible to a greater or lesser degree. Fungal pathogens are the primary causal agent of butt rot and attack the moist, vulnerable and under-protected lower portion of a tree trunk where it's largest diameter is recorded.

A tree is most vulnerable to rot where the bottom end of the trunk stem makes contact with the soil. The tree butt's location, when diseased, can attack the roots as well causing a disease known as root rot. These kinds of infections are likely to impair the transport properties of the xylem tissue found in the cambial region under the tree bark.

Again, It also weakens the stem and makes the plant more vulnerable to toppling.

Rot in the area of the tree butt can spread to the roots and/or move up and into the tree "compartment" producing a roughly conical column of dead, rotted wood which increases in size proportional to a tree's age and ability to compartmentalize and stop the spread.

These wood-decay diseases can start as a root or butt disease but can overlap as both root and stem decays. Most are caused by Basidiomycota or fungi. They may get in through wounds in the lower part of the tree or penetrate roots directly.

Understanding a Butt Log  and It's Quality

The highest quality logs typically come from the first or lowest section called the butt log by timber harvesters. The butt log is where the best, highest quality wood veneer and lumber is found. Wood veneer (usually hardwood) that is sliced or plywood (usually pine) that is rotary cut command high prices. It should be noted that high-quality trees with butt log damage or disease will negatively effect what will be paid at the timber harvest time.​

Buyers of veneer and plywood quality wood will require certain minimum log lengths depending on the mill's operation and set up.

 A common minimum used in North America is 8 feet plus an extra 6 inches for trim allowance. However, different veneer markets have different requirements for species, wood color and grain quality and can take logs as long as 11 feet plus 6 inches. Top grade veneer logs may have a 14-inch diameter minimum and extra prime grade can only come from the first butt cut.

What is Tree Butt Swell?

All trees will have some taper but the most valuable timber tree will maintain a "cylinder-like" form extending up the trunk. Any extra expansion of tree trunk butt above the normal stump flare is called butt swell and is normal in some tree species (especially trees on wet sites like cypress and tupelo gum).

Sound wood within the butt swell can be used but only as non-construction materials including wood chips and specialty items.

Timber cutters are recommended to cut above the swell for construction logs. Butt swell is considered a defect for veneer logs.