Buttress roots and trunk flutes: what the sources say
Buttress roots are wide ridges where the trunk meets the large roots, and flutes are the grooves between them or down a trunk. A native-plant glossary, a pull-test study on red maple, a Forest Service research note and a tropical forest study describe what each is and what they report about it.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page describes what the named sources say. It does not diagnose a tree, say whether any tree or growth is safe or unsafe, or tell anyone to cut, keep or treat one. Each cause and claim belongs to the source that gives it.
What the sources call a buttress and a flute
The Master Gardeners of Northern Virginia illustrated glossary defines a flute as a vertical fold or groove in the stem of a tree. It says uneven growth around the stem makes flutes, which can run in a spiral down from a branch union or up from the root collar, usually in the lowest log of the trunk. For buttress roots it passes on a definition from a 2018 paper (Dean and others, AoB PLANTS), in which Kent Julin describes flutes as the hollows lying between the spurs, the ridges where the buttress ties the trunk to the big side roots. A 2014 study in Arboriculture and Urban Forestry (Smiley, Holmes and Fraedrich) describes buttress roots as roots at the foot of the tree that hold it up and spread mechanical stress evenly, citing Lilly (2011).
Where the sources place them
| Source | What it says |
|---|---|
| Master Gardeners of Northern Virginia glossary | Buttress roots are typical of shallowly rooted trees in tropical forests, but can also be found on large, old trees in temperate climates. It says smooth, fluted bark is a distinguishing genetic characteristic of American hornbeam and that eastern redcedar trunks are often fluted. It says genetics may be responsible for fluting in some trees and that flutes might also result from environmental factors. In western hemlock stands along the southeastern Alaska coast it says fluting is common and may run from root to crown, with a genetic predisposition plus "catastrophic disturbances such as clearcutting or windthrow" possibly contributing, as reported by Julin and Farr (1989). It says bald cypress develops butt swell with age and is usually deeply fluted with substantial roots. |
| Frontiers in Plant Science, 2025 (Wang and others) | Calls buttress roots a common feature of the above-ground part of most tropical forests, and says trees evolved them mainly because competition for resources meant trees had to grow quickly to reach the sunlight, which needed more structural support. In its Diaoluo Mountain plot in China, 69.57 percent of the buttress-rooted trees had 3 to 5 buttress roots per tree, and buttress roots made up 16.18 percent of total tree biomass. |
| Arboriculture and Urban Forestry, 2014 | The red maple trees in the study had 6 to 10 buttress roots. |
What the studies report
In the 2014 pull-test study, ten plantation-grown red maples were pulled to one degree from vertical with measured force while roots were severed one at a time near the trunk, until roots had been cut from 50 percent of the circumference. The authors report that the force measured fell in a nearly straight-line relation to the number of roots severed. They say that when buttress roots are significantly decayed or pruned, tree stability is reduced, citing earlier work by Smiley (2008). The same paper says little study has gone into how much root loss it takes to raise the chance of failure. For how tree risk assessment treats this, see tree risk assessment.
A US Forest Service research note (Kessler, North Central Forest Experiment Station, Research Note NC-358, 1992) reports a possible link between injuries at the base of the trunk and buttress roots and dieback of branches on black oak in forests of southern Illinois. Its keywords list Armillaria, borer, canker and Cryphonectria, and the abstract states an association as possible, not as a cause.
The 2025 tropical study reports that soil organic carbon was higher on average by 20.8 percent in the upslope areas with buttress roots, and that those areas had lower soil temperature and higher soil moisture than the other sectors measured.
Whether the sources call fluting harmful
The glossary says fluting can reduce a tree's lumber value, especially when the flutes are deeply incised into the butt, and that flutes may provide habitat for insects and thereby food for birds. For work near the root zone of a large tree, see trees and construction.
Other growth forms are on the odd tree growth page.
Sources
- Master Gardeners of Northern Virginia, Illustrated Glossary: Flute, read October 9, 2026
- Arboriculture and Urban Forestry, Pruning of Buttress Roots and Stability Changes of Red Maple (Smiley, Holmes and Fraedrich), July 2014, read October 9, 2026
- US Forest Service Research and Development, Basal Trunk and Buttress Root Injuries May Be Associated with Branch Dieback in Black Oak (Kessler, Research Note NC-358), 1992, read October 9, 2026
- Frontiers in Plant Science via PubMed Central, An assessment of the role of buttress roots in the carbon stocks of tropical forests (Wang and others), 2025, read October 9, 2026