What’s in that Woodpile? Firewood Identification Firewood is a pathway for movement of invasive species. Knowing the species of wood a pest is found on or in can provide clues to identifying the pest.

Since so many problems are associated with the transport of firewood, firewood identification is becoming a more important monitoring tool. How might we begin to identify the species of wood found in this firewood pile?

Wood Id: Key Characteristics Presence or absence of pitch Bark Color Pattern Thickness Cellular structures Wood color Density Odor

Hardwoods-Softwoods Types and arrangement of cells Pores (Vessels) Ring and diffuse porous Ray cells Fibers Softwoods/Conifer Tracheids Resin canals Firewood will either fall into the softwood or the hardwood category. Neither category refers to the strength of the wood, rather it is based on whether the tree is a gymnosperm or angiosperm. Hardwoods are more complex and thus easier to identify without magnification. Softwood anatomy is less complicated than hardwood anatomy thus there are fewer features to use for identification. Hardwood vessels or pore size and arrangement are keys to identification. The presence or absence of ray cells can distinguish between oak and ash as well as other species. The fibers, parenchyma and tracheid cells create both texture and color in the hardwoods. In softwoods tracheids are the most common type of cell and are responsible for the wood texture. Actually it is the cell diameter of the tracheid that produces the texture. Resin canals are not cells but spaces between specialized epithelial cells. These occur in four genera, pines, larch, spruce and douglas-fir

Ring Porous Hardwoods Ring porous woods have large pores in earlywood (spring) and small pores in latewood (summer) Earlywood (spring) shows as obvious lines Hardwoods are further classified as either ring porous or diffuse porous. Ring porous woods have distinct “layers” of wood within an annual growth ring. The spring or earlywood is comprised of larger vessels (pores), while the slower growing summer or late wood produces pores that are very small in diameter and tightly arranged. In the heartwood (the discolored center wood of some cross sections), the spring wood often looks lighter in color. In sapwood (the lighter, not discolored wood in cross sections), the spring wood often looks a bit darker. The point is, with a hand lens or strong eye sight, one can distinguish the layers of spring versus summer wood. Most firewood that needs to be monitored for invasive pests is ring porous.

Hardwood - Ring Porous Black Ash All ash are ring porous, such as this black ash.

Hardwood - Ring Porous Green Ash All ashes are ring porous, such as this black ash.

Hardwood - Ring Porous Bur Oak All oaks are ring porous.

Hardwood - Ring Porous American Elm So, for most firewood monitoring instances, ring porous woods are the potential vectors. For example, oak wilt, Dutch elm disease, emerald ash borer. It’s not always so easy to distinguish between ring and diffuse porous pieces of firewood, but there are some other unique characteristics. For instance, the bark cross sections of rock and American elm have a two-colored, layered appearance. This is sometime referred to as “bacon strips,” or “oreo cookie” bark. American and rock elm bark cross section has a “oreo cookie” effect or alternating light dark pattern

Hardwoods - Diffuse Porous Pores about same size Pores distributed evenly throughout the growth ring Diffuse porous woods do not have the distinct layers of spring and summer wood. The wood within an annual growth rings appears fairly homogenous.

Hardwood - Diffuse Porous Basswood The flame pattern in the bark is also characteristic of basswood Basswood (Tilia, Linden) is a classic example of diffuse porous wood.

Hardwood - Diffuse Porous Boxelder Boxelder and all other maples are diffuse porous.

Hardwood - Diffuse Porous Big Toothed Aspen Most species of Populus including big-toothed aspen are diffuse porous.

Hardwood - Semi Ring Porous Black Walnut Medium brown to dark chocolate heartwood. Black Walnut Semi-Ring-Porous Hardwoods Pores: earlywood pores fairly large, decreasing gradually to quite small in outer latewood; pores solitary or in radial multiples of 2 to several Rays: fine, visible but not conspicuous with hand lens, 1-5 seriate, cells appear round in tangential view

Bark Hackberry Hackberry has Corky Ridges on Bark Elms and hackberry are often confused for each other, but hackberry does not have the “bacon strip” bark in cross section, and American elm does not have the characteristic corky or “warty” bark that hackberry has.

Cell Arrangement Elm and Hackberry American Elm Elms and hackberry also have kind of a unique characteristic to their summer wood. If you look at the wood in cross section, it has kind of a wavy “tiretrack” appearance to the summer wood. This is most noticeable with a hand lens. Both have wavy (tire track) latewood (summer)

Rays Oak Rays Oak and ash cross sections can look very similar, but oaks have distinct parenchymal rays, whereas ash don’t.

No Visible Rays Ash Cracks or Checks, but not Rays Sometimes when ash firewood cracks or checks, it may look like rays, but if examined closer it’s obvious that these lines are random cracks and not continuous rays.

Let’s Quiz the Log Splitter! This is strictly for fun and to wake people up. Feel free to skip it for the First Detector training. These are representatives of a state-wide survey conducted by the Department of Forest Resources, Outreach and Extension. The survey focussed on determining the 20, most-common species of firewood found in Minnesota.

Which log is hardwood?

Which log is hardwood? Log on the left Log on the right Response Counter

What is this?

What is this? Oak Ash Walnut It’s a conifer I don’t know Response Counter

What is this?

What is this? Maple Oak Walnut Pine Don’t know. Response Counter

Which one is ash? Lightly green, photosynthetic bark with diamond shaped patterns to the development of older bark.

Which one is ash? Pictures on the left Pictures on the right Response Counter

Resource for Wood Id Identifying Wood: Accurate Results with Simple Tools by R. Bruce Hoadley Taunton Press, 1990 Under $30

Gary Johnson UM Urban & Community Forester University of Minnesota Extension Foresters: Angela Gupta, Rochester Mike Reichenbach, Cloquet Gary Wyatt, Mankato