CITESwoodID: descriptions, illustrations, identification, and information retrieval

H.G. Richter, K. Gembruch, G. Koch

Authors

CITESwoodID was developed between June and November 2005, in response to a proposal by the German CITES Scientific Authority. It was carried out by K. Gembruch and Dr. H.G. Richter, in cooperation with Dr. G. Koch, at the Thünen-Institute, Hamburg, Germany, and to this day is available in the four languages English, German, French and Spanish. Subsequent updates (2008 and 2013) were put into effect by the latter two authors.

Species included

At present the database contains a) the 22 CITES protected timbers (19 hardwoods, 3 softwoods) known for their potential in the manufacture of lumber and downstream processing into products, and b) 34 trade timbers which can be easily mistaken for CITES protected timbers due to a very similar appearance and/or structural pattern. In few individual cases CITES protected plants/trees utilized for non-wood products have also been included.

Introduction

CITESwoodID enables the user to identify by means of macroscopic characters trade timbers which are controlled under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Macroscopic characters are all those which can be observed or perceived, respectively, with the unaided eye and a hand lens of approximately 10-fold magnification. The database also offers access to descriptions and illustrations of additional, unprotected timbers which are so similar to the respective CITES timbers that they can easily be mistaken for the latter.

The data are recorded in the DELTA System, and the interactive key uses the program Intkey – see delta-intkey.com.

Particular care has been taken to provide high quality photographic illustrations with the database of both the characters used for identification and the timbers comprising the database. The photo macrographs of transverse sections were taken at a magnification commensurate with that of a common hand lens (ca. 10-fold). Illustrations of wood surfaces are reproduced in natural size (1:1). These illustrations provide an excellent means of visualizing certain character expressions and directly compare the results of an identification run and the unknown object to be identified. Furthermore, nearly all characters used for description and identification are accompanied by explanatory notes with definitions, examples, procedures, etc..

CITESwoodID serves as a visual (illustrations) and textual (descriptions) identification aid to all institutions and persons involved in controlling the import as well as export of wood and wood products under particular consideration of CITES regulations. It also caters to all primary and secondary educational facilities with a curriculum related to forestry, forest products, and related subjects. Moreover, continuous use of the system is extensively self-educating to the effect that, after some time, even persons unfamiliar with wood and its structure can use it successfully.

Ever since wood identification became a necessity with the advent of more and more foreign timbers in local and regional markets, macroscopic characters were part of the process, primarily serving as a first indication as to what an unknown timber might be. Final identification was left to microscopic scrutiny as it offers a range of additional structural features for species recognition. While this situation has not changed, the circumstances have. Wood identification has become, by necessity, a vital part of quality control exercised by importers and manufacturers and, for that matter, now by CITES authorities. However, practitioners do not usually possess the sophisticated infrastructure, i.e., laboratory equipment and reference collections, required for microscopic identification. Hence, macroscopically visible features are the only means to provisionally satisfy quality control requirements and verify whether a given timber is correctly named.

From the beginning it must be quite clear to the user that the possibilities of macroscopic wood identification are much more limited than those of microscopic study. Firstly, the number of characters available for observation is considerably smaller. Secondly, in macroscopic identification one has to rely quite often on characters subject to a high variability due to different growth conditions of the tree (viz. formation of growth rings) or exposure to oxygen and UV radiation (viz. wood color). This may lead to subjective judgment by the user, and errors which might result in wrong decisions. In fact, in cases of closely related trade timbers, the use of macroscopic characters will end with a choice of several likely matches whose safe separation must be left to microscopic study performed by any of the scientific institutions in Europe with the necessary equipment and experienced staff — in Germany the Thünen-Institute, Hamburg (http://www.ti.bund.de).

Planes of observation

Wood identification is based on observations in the following planes:

•           Transverse (perpendicular to the stem axis),

•           Radial (parallel to the stem axis) and

•           Tangential (parallel to the stem axis),

plane (often also referred to as “face”, “section” or “surface”).

Observations made in these different planes add up to a three-dimensional picture of the gross wood structure. Observed differences in structure between the various timbers can be described, attributed to certain characters, and used for wood identification with the help of reference material for comparison.

Transverse plane is sometimes also called a cross-sectional plane or simply a cross section. For macroscopic and microscopic wood identification, the transverse plane usually offers the most useful diagnostic information about type, distribution, and arrangement of the axially orientated wood tissues, including the important growth ring characteristics. Even a very small transverse area may still reveal more information about the wood structure (composition) than large longitudinal (radial and/or tangential) surfaces. However, there are limits to how small a transverse area may be in order to still reveal useful structural details. In the case of thin (generally around 0.5 mm thick) veneers, for instance, typical structural patterns cannot be recognized in the transverse plane and need to be reconstructed from the corresponding patterns on longitudinal surfaces.

Radial plane is any plane whose surface parallels the stem axis and passes through the pith (in practice often referred to as “quarter sawn” surface). It exposes the longitudinal expression of the axially orientated tissues (vessels, axial parenchyma, fibers) transected at a 90° angle by bands of the horizontally oriented rays. However, because of slight irregularities in the structure (rays “curve” around large pores and often do not run in perfectly straight radial lines), exposure of the rays may be intermittent. The distinctive appearance of larger rays as dark bands (for instance in maple and black cherry) on a radial surface is called „ray fleck“. The term “silver grain” is often used with reference to the silvery sheen of very large rays (for instance oak) due to the reflection of incident light. Growth ring boundaries appear as nearly parallel axial/vertical lines in radial view.

Tangential plane like the radial plane, parallels the stem axis. However, its orientation is that of a tangent to the cylindrical growth rings and thus perpendicular to the rays at that point. Rays are visible in tangential view only if they are medium to large-sized; they usually appear as dark lines or lens-shaped flecks along the grain. Growth ring boundaries appear as U-shaped or V-shaped markings (superposed arcs). In practice tangentially cut boards or outer slabs are often referred to as “flat-sawn”.

For convenience, transverse, radial and tangential planes are often designated by the letters X (for cross-sectional), R (radial) and T (tangential), in the context of microscopic observation also as TS (transverse section), RLS (radial longitudinal section) and TLS (tangential longitudinal section). Due to the modest resolution of the unaided eye and hand lens, recognition of individual cells is all but impossible. Only the vessel elements of hardwoods and also the less frequent resin canals are generally large enough to be discerned individually, either as more or less circular openings in the transverse plane (pores) or as minute grooves (vessel lines) in the longitudinal planes. All other cell types (fibers, tracheids, and parenchyma) become macroscopically visible only when forming larger agglomerates (groups of cells) or tissues which differ from the surrounding tissues in shape and color.

Macroscopic structure of hardwoods

Hardwoods are composed of the following main tissues:

•           Fibers (mechanical support),

•           Parenchyma (storage and transport of nutrients),

•           Vessels (conduction of water) and, of rather rare occurrence,

•           Resin canals (secretory tissue).

In simple terms, fibers impart mechanical strength. They are responsible for resisting the many dynamic and static stresses in the living tree and in wood under load. Fibers usually make up the largest part of the wood volume. They are among the smallest diameter cells and, because of their often thick walls, appear as darker areas when seen en mass in cross section. At the macroscopic level they simply form a (usually darker) background for pores, rays and parenchyma.

Parenchyma cells are responsible for axial and radial transport and storage of nutrients in the living tree, and serve as depositories of accessory compounds during heartwood formation. Parenchyma tissues are orientated axially (parallel to the stem axis = axial parenchyma) or horizontally (perpendicular to the stem axis = rays). Parenchyma cells are nearly always thin-walled and become visible macroscopically only when forming larger agglomerates. In hardwoods the axial parenchyma can be very conspicuous and its various expressions are of high diagnostic value.

The rays also have an important role in macroscopic wood identification, particularly as regards size (width and height) and arrangement on tangential surfaces (storied vs. not storied).

The vessels of hardwoods constitute the principal passageways in the living tree for axial transport of water from the roots to the crown. On cross sections they are visible as pores (openings) arranged in a variety of distinctive patterns, on longitudinal sections as shallow grooves (vessel lines) which, depending on diameter and presence or absence of contents, may have a conspicuous and unique appearance. Vessels are the only cells which grow to dimensions (diameter, length) visible to the unaided eye or with a hand lens.

Few hardwoods also possess longitudinal and/or radial (forming part of a ray) resin canals, tubular passages in wood which are actually intercellular spaces surrounded by specialized secretory cells. Resin canals are a characteristic feature of some tropical timbers, for instance of the large Dipterocarpaceae family. Presence vs. absence, size and arrangement of axial resin canals are often highly diagnostic features. On cross sections resin canals are difficult to distinguish from the vessels/pores unless still exuding resin (dark irregular patches around the openings) or containing crystallized dry resin of a brilliant white color.

Macroscopic structure of softwoods

Conifers, here referred to as softwoods, evolved on earth before the angiosperms (hardwoods), and retain a relatively primitive wood structure compared with the more specialized and complex structure of hardwoods. Because macroscopic identification of softwoods is much more difficult due to the lack of distinctive features they are discussed here last. Essentially, softwoods are characterized by only three cell elements or tissues:

•           Tracheids (combined mechanical and conductive functions),

•           Parenchyma (storage tissue), and

•           Resin canals (secretory tissue).

The tracheids of softwoods serve the combined functions of mechanical strength and conduction. Their diameter is highly variable and rarely large enough to become visible under a 6x-12x magnifying lens. Nevertheless, tracheids produced early and late in the growing season of a tree may differ in size and, particularly, cell wall thickness, thus forming lighter colored early wood and darker colored latewood. Latewood width and the appearance of the transition of early wood to latewood within a growth ring is, in some instances, a very useful feature in macroscopic softwood identification.

Axial parenchyma cells, though present in many softwoods, never form large enough agglomerates to become macroscopically visible. Rays in all softwoods are generally uniseriate (narrow) and low, and therefore cannot contribute to the distinction of individual softwood timbers. Rays containing radial resin canals (“fusiform rays”) are the exception to the rule and, when large enough, may be a useful feature in softwood identification.

Resin canals occur in all species of several genera within the Pine family (Pinaceae), among them pines (Pinus spp.), spruces (Picea spp.), larches (Larix spp.) and Douglas-fir (Pseudotsuga spp.) which contain both axial and radial resin canals. The presence of resin canals thus provides an initial basis for separating pine, spruce, larch and Douglas-fir from the remaining conifers. Size, frequency and arrangement of axial resin canals can be helpful for distinction between and within these four taxonomic groups.

Colour calibration of images

The color illustrations of longitudinal wood surfaces have been adjusted “true to color” using a high quality conventional monitor calibrated in the ADOBE-GAMMA system. However, color reproduction cannot be trusted completely as in most cases; conventional monitors in use are simply not calibrated in the ADOBE-GAMMA system or else, cannot be calibrated at all as for instance most TFT monitors.

Supplementary information

The character list features a number of text “characters” for entry of additional observations or comments under the various main topics. These text characters are used to store information on particular attributes of a given timber which are not covered by the other, rigidly structured characters. However, when the need arises to distinguish between two or more nearly identical timbers such additional observations may assume a highly diagnostic value and thus facilitate a final decision at the end of an identification, either by comparing the full descriptions of the species or using the Intkey ‘Differences’ function (see below).

How to use Intkey for wood identification and information retrieval

Specimen preparation

Observations of wood structural and other features are made on transverse and longitudinal faces. A fresh end grain cut is an absolute necessity as only a clean surface will reveal sufficient details of wood structure. A carpet knife with (high quality) disposable blades is recommended for end grain cutting. The blade should always be moved in a sliding motion to produce clean cuts. Hand or machine planing usually yield clean enough longitudinal surfaces for observation. Just as important as clean cuts is adequate lighting which greatly enhances observation with the unaided eye or with a hand lens. Be sure to turn the specimen at various angles under the light as the reflectivity of wood tissues varies under different light angles. With very soft woods use a flexible razor blade. Very hard woods often require several overlapping strokes with the knife to produce a clean surface large enough for initial evaluation of macroscopic features. Fixing the specimen in a vice is recommended when dealing with very hard timbers. Change blades frequently because the inevitable nicks will leave traces on the cut surface which may obscure details of wood structure or may even are mistaken for such.

Identification

The Intkey screen is divided into four panes (1a; 1b; 2a; 2b of the illustration) which allow the user to follow the steps of an identification.

By default, the available characters are automatically listed in a sequence of “Best Characters”. Your identification will usually be quicker and more accurate if you use characters near the top of the list. If you want to use a particular character without visually scanning the whole list to find it, use the button  (“Find text in characters”). A further option is using the button  (“Natural order”) to display the available characters as ordered in the original character list. To return to “best” order, use the button  (“'Best' order”).

Available characters (upper left pane), used characters (lower left pane), remaining taxa (upper right pane) and eliminated taxa (lower right pane) will be indicated after each step of an identification.

Be sure to operate with positive affirmative character states as long as possible. Using negative states, for instance “absent”, bears considerable risk of going the wrong way as “present” may indeed be a fact (and be coded that way in the database) but may be overlooked by the user at first sight.

Most characters are accompanied by explanatory notes with information on definitions, explanations as to how observations can be correctly interpreted, procedures concerning specimen preparation for certain purposes, examples of timbers with a very typical expression of the character in questions, cautionary notes on how to guard against misinterpretation, information on specific wood characters not covered by the character list, etc. In addition, characters and the timbers in the database are accompanied by high quality color images illustrating important macroscopic features on both transverse and longitudinal faces. These images can be of considerable help in finding a character and using it in an appropriate way. Images are also very useful when it comes to confirming (or rejecting) identification results by visual comparison.

Information retrieval

The button  (“Introduction and references”) allows you to access, via a Web browser, the following information: an introduction to the database (this file); the character list, with and without explanatory notes; abbreviations (internal codes used in the database); implicit attributes; acknowledgements; references; citation; and contacts, disclaimer, and copyright.

The button  (“Information about taxa”) opens a window where descriptions of the taxa as well as the accompanying illustrations are available.

Differences between remaining taxa (text and pictures)

Macroscopic identification, even if done to the best of knowledge, will often result in a choice of several similar timbers which are difficult or even impossible to separate with the help of the still available characters. In such cases, clicking the button  (“Differences”) will produce a list of differences between selected timbers either for all characters or for a selected subset of characters.

The button  (“Information about taxa”) allows images of timbers to be viewed together for direct comparison.

A careful comparison of the listed differences and the images might give valuable hints for successfully matching an unknown timber with one of the remaining taxa.

Learning more about Intkey

The program is initially in “Normal Mode”, which is suitable for most purposes. For more options, select “Advanced Mode” from the “File” menu.

Help for all the Intkey options is available in Advanced Mode.

Worked examples using Intkey for identification and information retrieval are available at http://delta-intkey.com under “Overview of the DELTA System”.


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