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GROWTH RINGS


NOTE: for identification of specific species, there are links
at the bottom of this page (click) that will take you on a
guided tour of 2998 detailed images of 1068 species


INTRODUCTION


transverse sections showing full sets of growth rings


There are two basic conditions in which trees grow. These are temperate zones, with a climate that has varying seasons, with a warm summer and cold winter, and tropical zones, with a climate that has only very mildly varying, even unchanging, seasons or summer and winter. In temperate zones, trees grow in summer and go dormant in winter and this constitutes as growth season. In tropical zones there is little to no difference between summer and winter, so the concept of a "growth season" is not applicable.

In the spring when the trees in a temperate zone start to grow for the year that new growth is called earlywood (or, less commonly, spring wood) and in the late summer as growth slows the growth area is called latewood (or, less commonly, summer wood). This cycle of earlywood and latewood gives rise to rings in the tree, called growth rings. The exact transition from earlywood to latewood varies from very clear to quite vague.

The nature of these rings depends on the kind of tree, the two basic types being hardwoods and softwoods. These terms are based on the fact that in general (but NOT as anything like an absolute rule) hardwoods are harder than softwoods, and the names derive from that fact. Technically, hardwoods are angiosperms (trees that drop their leaves in the fall), and softwoods are gymnosperms (trees that keep their leaves, or needles, throughout the year). A fairly strong generalization, but not an absolute rule, that can help you know which is which for some types of tree is as follows: trees that bear nuts (chestnut, hickory, etc.) and trees that bear fruits with a "pit" inside, which is the seed (apple, pear, etc.) are all hardwoods and trees that have needles and/or cones are softwoods.



Annual growth rings --- Trees in temperate climates grow at different rates during the seasons, ranging from exuberant early growth in the spring when the sap is flowing in the tree and in the early summer, to a slower late growth in the late summer and fall, becoming more sluggish and then dormant as the winter sets in and then essentially none in the winter itself. The early growth is typically wider, less dense, weaker, and more porous (in hardwoods) than the late growth and in many cases is significantly lighter in color. These seasonal growth spurts create differing cell structures which, when a tree is cut perpendicular to the axis of growth, show up as what are called "rings", for the obvious reason that they are, geometrically speaking, a series of concentric rings that start at the center of the tree and occur outward, one for every year of the tree's growth. NOTE: false rings occur in some species, sometimes due to a late frost, others due to unknown reasons.

Tree rings can be counted to tell how old a tree is, and the size of the rings can tell a lot about the growth conditions of their year. Drought years have narrow growth rings as opposed to years of plentiful rain, which have wide growth rings. By working with long-dead trees, whose growth rings ended many years ago, and overlapping them with trees whose earliest growth rings happened before the older tree died, scientists have been able to date some events back for several thousand years. This is the science of dendrochronology.

Trees that grow in tropical zones (that is geographic regions where there is little change in climate throughout the year) grow pretty much the same amount every day throughout the year and consequently have little variation in texture. In some temperate zone species (e.g. black gum and sweet gum) and many tropical species, particularly those whose growth ranges do not get too far from the equator, annual growth rings can be anything from very hard to detect to essentially non-existent.

There are many ways that one can distinguish among different trees based on the growth rings. First, there are macro (large scale) characteristics and then micro (small scale) characteristics. Micro characterises can be viewed by eye, with a 10X hand lens, or in a microscope. Because this site is not for wood scientists or botanists, but rather for woodworkers, I am only going to discuss viewing by eye and by hand lens.



Macro growth ring characteristics --- Macro characteristics of growth rings can be put into numerous categories. I find the three most helpful to be those that are readily apparent to the naked eye, which are:
Many species have a wide range of rings per inch but most species are fairly consistent with their texture and visibility. Here are representative examples of various woods showing these three characteristics:

representative examples of ring appearance --- VISIBILITY
strong / clear
Lebanon cedar
strong / clear
Russian olive
weak / faint
basswood
weak / faint
narrowleaf cottonwood
vague / non-existent
Amazon rosewood
vague / non-existent
Madagascar rosewood


representative examples of ring appearance --- COUNT
2 rings / inch
redwood
8 rings / inch
beech
40 rings / inch
old growth Douglas fir
Showing a wide range of rings/inch from plank to plank. Redwood can have a high ring
count and Douglas fir can have a fairly low ring count. These examples are just to
show representative example of the COUNTS, not of these particular species


representative examples of ring appearance --- COUNT
4 rings / inch
Douglas fir
40 rings / inch
old growth Douglas fir
Showing a highly variable count within a single species


representative examples of ring appearance --- COUNT
1/4" x 1" cross section of English brown oak with the pith to the left and the bark to the right and showing a variable
ring count in a single piece of wood, which happens if there are years of good growth (wide rings) and years
of poor growth (narrow rings). This tree had a lot of bad years in a row there in the middle. In the early
and late years it has about 14 rings/inch but in the middle years it has more like 50 rings/inch


representative examples of ring appearance --- TEXTURE
coarse
black oak
smooth
grand fir




Micro growth ring characteristics --- A discussion of the micro scale characteristics of growth rings is best done with separate discussions of hardwoods and softwoods since they have significantly different characteristics.

GROWTH RINGS IN SOFTWOODS: NEED DISCUSSION

GROWTH RINGS IN HARDWOODS: NEED MORE DISCUSSION THAN JUST WHAT FOLLOWS

Pores Individually and in small groups:

Hardwoods have little hollow tubes running up and down the tree called pores. The fundamental factors in the identification of various hardwood are based on characteristics of pores, both how they look individually and in small groups and how they are arranged in larger structures. The most obvious first-level characterization of hardwoods is how the pores are arranged in groups in the growth rings but those are the most macro characteristics and are best understood by first looking at pores at a more micro level, both individually and in small groups.

Pores can be looked at in cross-sections that show them running up and down the tree (a radial or tangential cross-section) and they can be looked at in a cross-section that looks down into the pore (an end grain cross-section, formally called a transverse cross section). For the purposes of this article, I will only use end grain cross sections.

The main characteristics of pores taken individually are size, (that is, their diameter), and density, (that is, how many of them are there in a given area). Another significant factor is the kind of parenchyma cells that surround the pores but that is discussed on the parenchyma page (which also discusses other aspects of parenchyma) and is not repeated here.

Pore sizes range from large enough to be easily seen with the naked eye in end grain cross section, such as in the earlywood of most oaks, down to sizes so small that they cannot be individually distinguished even with a 10X loupe and could only be studied with a microscope, such as in most fruitwoods. I'm not going where only microscopes can go, other than perhaps a mention in passing here and there. Some types of wood have all or most of the pores with the same size, others have a modest range of pore sizes, and some have a wide range of pore sizes (most oaks, for example)

Pore densities range from very sparse, perhaps 100 or so per square inch of end grain cross section in some pieces of cocobolo, which has an unusually sparse pore count, up to so small and jam-packed as to be commonly described as "uncountable", a description which is not literally true but which IS true for all practical purposes in all cases and IS literally true when you have nothing more than a 10X loupe to work with. Most commonly, pore counts are very high, ranging from many hundreds to many thousands per square inch. This kind of numeric specificity on ring count is not something that is generally used in talking about wood anatomy, particularly at the level of this article. More commonly it's just said that the pores are sparse, medium, dense, and uncountable (meaning very dense indeed).

representative examples of pore density and sizes
(images are 1/4" square end grain cross sections shown here at 9X)
SPARSE
(mockernut hickory)
large to tiny pores
MEDIUM
(tropical walnut)
medium to small pores
DENSE
birch
small pores
UNCOUNTABLE
apple
tiny pores


Pores In Larger Groups

At the next level above individual pores and small groups, it is informative to look at how pores exist in various woods in larger groupings of various shapes and sizes. The fundamental arrangement of pores includes random distribution of individual pores in addition to groups. Random pore distribution occurs in many diffuse porous woods such as most of the rosewoods. These groupings can overlap and more than one can exist in the same piece of wood. Groupings include:





representative examples of pore multiples
random individual pores
(extremely sparse)
pore multiples
(in various orientations)
internet blowup showing
different multiple lengths
It's important to note that just because two pores are smashed up next to each other it does not mean that they share a common cell wall. This is excellently (and, I have to admit, accidentally) illustrated by the pic that is 2nd from the right in the upper row where I have circled a couple of pairs. These are not a multiple pore configuration, I was just a bit too fast in selecting pics for this illustration. No, wait ... actually, I did this on purpose to illustrate this point. Yeah, that's it. On purpose! That's my story and I'm sticking with it.

representative examples of pores in radial strands and wavy bands
radial strands
wavy bands


representative examples of pores in dendritic groups
some of the many "looks" of dendritic groups




Pores in the Aggregate: Ring Porous, Diffuse Porous, and Semi Ring Porous (aka Semi Diffuse Porous)

Because hardwoods have pores, the growth rings are usually very easy to see, although not invariably so. The arrangements of the pores and their relative size throughout the growth season generally fall nicely into one of three categories, although it CAN get a little vague sometimes as to where the boundaries are.

The three types are ring porous, diffuse porous, and a middle one that is called either semi ring porous or semi diffuse porous depending on whether it is closer to ring porous or closer to diffuse porous. Some references make little or no distinction between the two "semi" types and just name everything in between clearly ring porous and clearly diffuse porous as semi ring porous. I have done my best in this document to show the distinction between semi ring porous and semi diffuse porous but it can be a hard call and I don't think it's worth too much effort anyway since it gets a bit subjective.

Ring porous woods have a very clear line of large pores in the earlywood, transitioning quickly to noticeably smaller pores, even down to tiny pores, in the latewood. In these woods, the transition from earlywood to latewood is very clear and even more clear is the demarcation between latewood and the following earlywood. Diffuse porous wood have uniform-sized pores running throughout the growth ring so that the demarcation between latewood and earlywood can be hard to discern, or even missing entirely.

In between the two, to varying degrees, is a type that has relatively large pores in the earlywood, trailing off smoothly to relatively small pores in the latewood with no sudden jumps in pore size. In such woods the transition from earlywood to late wood is not clear. Usually, but not necessarily, there is a clear demarcation between the latewood of one ring and the earlywood of the next ring. If such a wood looks mostly like ring porous, it is called semi ring porous and if it looks more like diffuse porous it is called semi diffuse porous.

For many woods, the distinction is quite clear but for others, not so much. Some woods can fall into TWO categories, either ring porous and semi ring porous or diffuse porous and semi diffuse porous. For example Tectona grandis (teak) can be either ring porous or semi ring porous. Again, some authors make little or no distinction between the two "semi" types and just name everything in between clearly ring porous and clearly diffuse porous as semi ring porous, and again, it can be a hard call just where the borderline is between ring porous and semi ring porous and between diffuse porous and semi diffuse porous.



The fundamental "look" of the types is:

representative examples of ring porosity types:
(images are 1/4" square end grain cross sections shown here at 9X)
RING POROUS
black oak
Quercus velutina
SEMI RING POROUS
teak
Tectona grandis
SEMI DIFFUSE POROUS
black willow
Salix nigra
DIFFUSE POROUS
birch
Betula spp.
NOTE: distinctions between ring porous and semi ring porous are often not as clear-cut as these examples show and the distinctions between semi diffuse porous and diffuse porous can be even more problematic.



More examples of each --- The point of the rest of this page from here to the links at the bottom is to help you know in advance which page or pages in the links (and their subpages) you should check for any mystery wood you may be trying to identify


To give a bit more of a feel for the "look" of the three types, here are examples of each, followed at the bottom of this page by links to pages for each of the three. These pages a large number of species for each type and I have included on those pages every wood for which I have personally taken end grain closeups that are suitable for use in this discussion. For those species that have a bit of a range in the look, and for which I have suitable images, I've included more than one pic each. There are about 625 pics of some 450 species shown (some species have multiple pics). Some woods, such as maple, may be represented by many different species. A few such even have their own page. Maple, for example, has a page showing 14 species, a few of which have multiple pics.


examples of ring porous
(images are 1/4" square end grain cross sections shown here at 9X)
black oak
quercus velutina
chinkapin oak
Quercus mohlenbergii
catalpa
catalpa spp
Northern catalpa
catalpa speciosa
American chestnut
castanea dentata
chinkapin
Castanopsis chrysophylla
english elm
Ulmus procera
mockernut hickory
Carya tomentosa


examples of diffuse porous
(images are 1/4" square end grain cross sections shown here at 9X)
birch
Betula spp
Eastern hophornbeam
Ostrya virginiana
chittamwood
Sideroxylon lanuginosum
kempas
Koompassia malaccensis
little-leaf linden
Tilia cordata
Madagascar rosewood
Dalbergia monticola
Oregon myrtle
Umbellularia californica
pear
Pyrus communis


example of semi ring porous
(images are 1/4" square end grain cross sections shown here at 9X)
camphor
Cinnamomum camphora
tamarisk
Tamarix spp
teak
Tectona grandis
Arizona black walnut
Juglans major


example of semi diffuse porous
(images are 1/4" square end grain cross sections shown here at 9X)
European beech
Fagus sylvatica
butternut
Juglans spp
amendoim
Pterogyne nitens
peachleaf willow
Salix amygdaloides




Extensive further examples

(automatic stats)
2998 pics of 1068 species at 12X

The links below go to pages for each type. Within each type, woods are arranged very loosely by general "look" for ease of matching up with "mystery woods" that you might be trying to identify and comments are made about the general characteristics of each type of wood.

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