Like all trees in the temperate regions of the world. Hardwood species put on an annual ring of growth. These rings can be easily seen in a cross section of a log or limb.
Each spring as trees break dormancy a new growth ring starts to form; these new cells are also called early wood. The tree grows through the summer adding more wood cells, this is latewood. In late fall early winter growth stops, and the tree goes dormant for the cold winter months.
Hardwood species can be grouped into 3 categories depending on their annual ring growth structure. These are ring porous, semi-ring porous and diffuse porous.
Ring Porous- These species which include oaks, ash, chestnuts and others produce large cells in the spring called vessels to transport large amounts of water for photosynthesis. These vessel cells are easily visible with the naked eye. Once these cells are formed, there is an abrupt change in cell formation in the latewood. More wood fiber is produced for structure and the vessels are smaller in size.
This tree most likely grew under larger trees for most of its life. The tight growth rings indicate it was starved of light and nutrients. Once the older trees were harvested, it was released and allowed to grow at a faster rate. Which you can see from the wider growth rings. With proper forest management, this can be avoided. Trained professionals can pick out the suppressed trees in a stand and have them removed with the overstory and allow the next generation of trees to grow unobstructed.
This repeated pattern of early wood and late wood is what gives oak is beautiful grain pattern.
Diffuse porous – The vessel cells of these species are all similar in size and spread evenly from early wood to late wood. This gives the wood of these species a smooth appearance and feel. Yellow poplar, hard and soft maple are some of the most common lumber species in the diffuse porous group.
Semi-Ring Porous- These species fall in-between ring porous and diffuse porous. Vessel cells will cluster in groups in the early wood and will gradually even out in the late wood. Unlike ring porous there is not abrupt transition from early wood to late wood. These species include black cherry and black walnut.
Why is this important in the world of log buying!? For one it helps to identify logs. It also helps to recognize issues within the log. Deformation in the rings can mean internal defects or poor growth habits which can lessen the value of a log. The rings can also tell us what happened in the life of a tree. Did it suffer a drought, suppression, lighting strikes, cattle grazing, logging damage, etc. All these forces will have a direct effect on the growth of a tree. Which in turn, will affect the lumber or veneer produced from the log.
In figure 4 you can see the difference in growth ring size from the center of the tree to the outside. Note the abrupt change in ring size. This is referred to as double textured. When this log is sawn two different grain patterns will be present. This causes issues when drying lumber and will have an inconsistent appearance.
