growth rings

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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 3170 detailed images of 1036 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:

visibility --- do the rings stand out strongly or are the harder to see? Many hardwood have extremely clear growth rings whereas tropical woods such as the rosewoods tend to not have visible growth rings
ring count --- how many rings are there per inch ? Trees that grow really quickly have very few growth rings per inch and at the other extreme, old growth trees can have a very large number of rings per inch. Many species can have an extremely wide range of growth ring counts, so ring counts are of limited utility in wood identification.
texture --- do the rings look smooth or do they look coarse? Most softwoods have smooth textured rings but hardwoods can have either (although they tend to be coarse)

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:

multiples --- pores growing with shared cell walls between contiguous pores

random arrangements --- two or more pores together in a random orientation
radial strands --- two or more pores together in a grouping that is oriented radially
tangential bands --- two or more pores together in a tangential band

radial strands --- lots of pores loosely associated in a long radial grouping that may be fairly straight or may wander a bit
wavy bands --- bands of pores that are sometimes short straight bands that are grouped in a way so as to look wavy, and sometimes pores grouped directly into bands that are themselves wavy. These are a form of confluent parenchyma
dendritic groups --- pores grouped in tree-like structures (sometimes with other vessels included)

thick --- lots of very small pores (and sometimes other vessels) in thick groups
sparse --- medium to small sized pores that are individually distinct but grouped in a very roughly tree-like structures

representative examples of pore multiples

random individual pores (extremely sparse)	pore multiples (in various orientations)	internet blowup showing different multiple lengths

random smattering of individual pores in a piece of cocobolo
various arrangements of multiple pores (individual images are 1/12" square end grain cross sections shown here at 12X). For those groups that are not oriented radially (radial being by far the most common orientation), I have emphasized the direction of the groups by adding a blue line.

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 ("ulmiform pore groups")

radial strands of pores is a fairly common occurrence and this is a pretty good showing of the range of "looks" the strands can take on
wavy bands of pores are very distinctive but relatively rare. Elm and hackberry (both shown here) are two of the few woods that have them. Elm in particular is so well known for them that an alternate term to "wavy bands" is "ulmiform" (meaning "having the form of elm") bands because elms are in the genus Ulmus and these bands are a distinctive feature of all elms.

representative examples of pores in dendritic groups

some of the many "looks" of dendritic groups

Dendritic groups usually are made up of either uncountable individual pores or tiny pores surrounded by other vessels, and that is mostly what is shown here. These groups occur in a number of woods and are particularly common in the oaks and chestnut. The upper left pic shows a fairly uncommon dendritic group of sharply distinct pores.

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.

ring porous --- Clear line of relatively large early wood pores, one to several thick, dropping quickly to much smaller pores in the latewood
semi ring porous --- well defined row of earlywood pores with a gradual change to smaller and smaller pores in the latewood rather than the abrupt change in size that is characteristic of ring porous
semi diffuse porous --- pores are almost the same size through the growth ring but are somewhat smaller, and usually a bit more sparse, at the end of the latewood so that there is a noticeable demarcation between latewood and the following earlywood. Also, semi diffuse porous often has darker tissue at the end of the latewood, which also helps make the growth ring boundaries look sharply defined.
diffuse porous --- pores are identical in size all the way through the growth ring so the growth ring boundaries are somewhere between thin and non-existent, sometimes distinguished by marginal parenchyma

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

black oak that is classic ring porous with a big obvious earlywood line of large pores and then going immediately to much smaller pores throughout the latewood
chinkapin oak with a clear line of earlywood pores just one pore deep and then going immediately to much smaller pores throughout the latewood
catalpa with an obvious line of earlywood pores that terminate fairly cleanly and graduate somewhat slowly to smaller and smaller pores in the latewood
Northern catalpa with an obvious line of early wood pores that graduates somewhat gradually to smaller pores in the latewood. This is a wood that is sometimes ring porous and sometimes semi ring porous and this sample is pushing close to semi ring porous
American chestnut with a clearly defined start to the earlywood but a somewhat slow transition to smaller pores in the latewood. The fairly thick, close-together pores in the early wood is how one can distinguish chestnut from chinkapin. The pores are encircled by vascular tracheids and parenchyma, forming dendritic groups
chinkapin with a clear earlywood line of spares, fairly evenly-spaced, pores in the earlywood changing immediately to smaller pores in the latewood and including the dendritic groups seen in chestnut (the sample just to the left) but clustered in somewhat of a "V" shape moving from earlywood to latewood
English elm with a clearly one-pore-thick line of earlywood then changing immediately to smaller pores in the latewood
mockernut hickory with a look that could be described as either ring porous or semi ring porous since the sparse line of earlywood pores graduates fairly evenly to smaller and smaller pores in the latewood. Since the pores in the latewood are not immediately smaller than those in the earlywood, this is really closer to semi ring porous. Hickories and pecans both include some species that are ring porous and some that are semi ring porous

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

birch with the classic diffuse porous look of identically sized pores spread evenly throughout the growth ring
Eastern hophornbeam with a fairly clear area of earlywood pores but with the same size pores moving into the latewood
chittamwood with pores that are fairly evenly sized in radial bands but encircled by vascular tracheids and parenchyma, forming dendritic (i.e. "treelike") groups
kempas with the classic diffuse porous look of identically sized pores spread evenly throughout the growth ring. These pores are surrounded by beautifully formed lozenge shaped groups of aliform parenchyma
little-leaf linden almost semi diffuse porous by virtue of the smaller sized pores towards the end of the latewood. This is a borderline call as to which it is, diffuse porous or semi diffuse porous
Madagascar rosewood with almost randomly spaced pores of pretty much the same size. This look is very common for tropical hardwoods in general the rosewoods in particular
Oregon myrtle with a look that is kept from being totally classical diffuse porous because it has some smaller pores right at the end of the latewood but I don't consider this enough to make it semi diffuse porous
pear with tiny same-sized pores throughout the growth ring which This is common in the fruit woods. By the end of the latewood growth the pores have become slightly smaller and less dense, thus causing a noticeably darker area at the end of the latewood than at the beginning of the next ring's earlywood. This type of demarcation between the two is fairly common in diffuse porous sand semi diffuse porous woods.

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)

3170 pics of 1036 species at 12X

To see ALL of the end grains as jpg images without titles but
with a mouseover that shows the type of wood and a link that
takes you to the anatomy page contining that wood, click HERE

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.

HARDWOODS

ring porous (168 pics of 41 species)
- includes: ailanthus, ash, autumn olive, blue mahoe, catalpa, chestnut, chinaberry, coffee tree, elm, hackberry,
  laburnum, locust, mulberry, oak, osage orange, paulownia, russian olive, sassafras, sen, sugarberry, sumac
semi ring porous (aka semi diffuse porous) (28 pics of 6 species)
- includes: almond and tamarisk, amendoim, butternut, camphor, hickory, live oak, narra, pecan, persimmon,
  redbud, smoketree, teak, walnut and a few others
diffuse porous (2490 pics of 842 species)

domestics (863 pics of 264 species)

includes: birch, fruitwoods (apple, cherry, pear, plum, etc.), hawthorn, maple, willow, and LOTS of other diffuse porous domestics

exotics (1627 pics of 578 species)

includes: the acacias, the ebonies, the eucalypts, the rosewoods, the mahogany family, The Shoreas, The Grasses, and LOTS of other exotics

SOFTWOODS (IN PROGRESS, not well organized as yet; mostly just alphabetical) (484 pics of 147 species)

includes: arborvitae, cedar, cypress, Douglas-fir, fir, hemlock, juniper, larch, pine, redwood, spruce, yew, and a few others

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