Hello - I'm a naturalist with the Huron-Clinton Metropark system in MIchigan and I'm writing new trail signs on forest ecology. While cutting wood samples for sign photographs, I've come across several hardwoods which have excessive growth on one side of the stem. This growth would be similar to compression wood in a leaning conifer; i.e. the ring growth is wider on one side than it is on the opposite side. Since tension wood is not supposed to grow like this, I can't find an explanation. The wood I've seen this in is mainly elm and ash. In some trunk samples there's nearly twice as much wood on one side of the core than the other. Any ideas as to what causes this? Thanks. Steve Horn

Greetings Steve,

Reaction wood in conifers, as you've indicated, is termed "compression" wood. Reaction wood in hardwoods, is termed "tension" wood. Trees that lean, are uprooted, bent from ice/snow, or trees growing on steep slopes, may often have this eccentric reaction wood trait.

According to R. Bruce Hoadley's "Understanding Wood"...reaction wood forms predominantly toward the upper side of the leaning stem. Because gravity causes the upper side to be in tension, it is termed tension wood. In hardwoods, however, there is less tendency than in softwoods for the pith to be off-center in the stem, and tension wood may develop irregularly around the entire stem...Indications of crookedness or sweep in the log are signals of possible tension wood.

Hopefully this helped!