IAWA Bulletin n.s., Vol. 10 (2),1989: 123-132

APPEARANCE AND PERIODICITY OF GROWTH RINGS IN SOME TROPICAL WOODS

by

Pierre Detienne Centre Technique Forestier Tropical, 45bis avenue de la Belle Gabrielle, 94736 Nogent-sur-Marne Cedex, France

Summary Trees belonging to 30 tropical African and thus calculating their growth rate; detecting South American hardwood species were variations in growth rate during the tree life wounded annually. This made it possible, or accurately dating phenomena that left after the trees had been felled, to mark pre­ traces in the wood, e.g. insect attack or slight cisey the annual growth rings and determine fire damage. their boundaries. These boundaries are al­ ways formed during the longest dry season Materials and Methods and clearly express the rhythm of cambial Experiments were carried out on 2 to 10 activity. The appearance and nature of these trees selected from 30 species belonging to growth rings vary according to genera rather 26 genera of 16 families, in Guinean-Congo­ than to types of climate. lese Africa and French Guiana. The species Key words: Annual growth rings, tropical are listed in Table 1. African and American hardwoods, wood The cambial activity was recorded every structure. two weeks with band dendrometers at a pre­ cision of 0.2 mm over periods of 4 to 7 years Introduction depending on species or observation stations. For a long time tropical trees have been The accurate detection of growth rings described as fast and continuously growing was accomplished thanks to scars left in the plants for their entire life span. Consequent­ wood by wounds inflicted on living trees. ly, the occurrence of annual growth rings in These wounds, 0.5 cm wide and 4 or 5 cm their wood was not acknowledged, although high, were made in the bark, up to the cam­ several authors had hinted at their existence, bium which was locally destroyed, but the yet without being able to demonstrate their wood was kept devoid of lesions. Wounding annual character (Chowdhury 1939, 1940; was done once a year, during the longest dry Alvim 1964), except in Swietenia mahagoni season, either between December and March Jack, Azadirachta indica Juss. and in Tectona in Guinean -Congolese Africa, or between grandis L.f. (Coster 1927). However, some July and September in French Guiana, authors succeeded in explaining periodicity in always at the same height in the trunk wood formation linking physiology and anat­ (Detienne & Barbier 1988). omy (Fahn 1958; de Fay 1986). Mter the trees had been annually wounded From 1965, studies have been carried out several times, they were felled and cross cut at the Centre Technique Forestier Tropical in­ at wound height. Mter drying, the end grain to the possible annual periodicity of diameter was sanded with extremely fine carborundum growth of tropical trees, and into the struc­ paper (400 grains per cm2). The scars left by tural characters by which this periodicity is the wounds were still quite visible and some­ marked in the wood. The knowledge of the times underlined by local formation of dis­ appearance and the annual periodicity of these coloured wood in species with well-defined variations can be applied to several problem heartwood (Figs. 1-5). Dating each scar was areas, e. g. determining the age of trees and performed easily, the oldest one being the

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most distant from the bark, the others short dry season, interruptions in cambial ac­ following from right to left or left to right tivity starting a few months before the dry according to the direction chosen to inflict the season or, but less frequently - and only in wounds. trees with very slow growth - temporary The growth rings are visible to the naked shifts in the normal rhythm. The possibility eye on trees with considerable growth during that these abnormalities were caused by phe­ the experiment. However, a magnifying lens nological events (e.g., massive flowering or (x 6 or x 12, or even x 25) is generally fruiting, top damaged by insect attack) cannot needed to determine the growth rings of most be excluded, but this has not been studied in species accurately (Figs. 1-5). detail.

Rhythm of cambial activity Appearance and nature of growth rings The trees studied always showed a rhyth­ The wood formed before the period of mical circumference increment. Our band complete standstill, or during the long period dendrometer measurements showed that the of reduced growth, generally shows a thin growth in trunk diameter generally starts layer of fibres with slightly thicker walls around the beginning of the rainy season and and/or with a more flattened outline in cross goes on, on a regular basis or not, until section than the others. The phenomenon is the long dry season, i.e. for 7 to 10 or similar to that observed in species of tem­ 11 months. Then the cambial activity either perate climates; however, it is less marked comes to a complete halt, or the growth rate and thus less clearly visible. Seen with a is clearly slowed down. magnifying lens, this thin layer of wood The complete halt lasts for various lengths looks slightly darker. This character is not of time depending on species, specific years, always very obvious, so it can be used only but, above all, on the vigour of the tree which in species with no variations in other tissues, may change with age or depend on external such as softwoods or hardwoods with a very factors such as for instance social position. low tissue proportion of parenchyma. Growth is generally interrupted for 15 days The only experiment on softwoods was up to 3 months, but sometimes for 6 months carried out on two trees of Agathis moorei in moderately vigorous trees, or even over Mast. from New Caledonia. The annual 1 year in weak and suppressed trees. In the growth ring boundary is marked by a thin latter case, on the disk of the felled tree, no dark band composed of fibres with thicker growth ring was shown to have been formed walls, but it may be blurred, or even invisible for such a period of time. In some species, on part of the section. The small number of a small decrease in the circumference was samples does not permit to define the real noted during the inactive period. This phe­ annual growth ring exactly; often individual nomenon can probably be attributed to a dark bands are only present on part of the slight contraction of the bark during the dry disk surface; these could represent false rings season. when they are only present in one sector; al­ Periods of reduced cambial activity during ternatively annual growth rings may be partly the long dry season were principally observ­ (locally) or completely missing. Such a dark ed in fast growth species or vigorous speci­ band formed by flattened fibres with thicker mens. They always last longer and/or their walls is also the only charactistic of the ring increment reduction is greater than in other boundaries of Yayamadou, Virola melinonii periods of slow growth occurring during the A.C. Smith (Myristicaceae). The transition vegetative period, e.g., during the short dry between this band of latewood and the lighter season. coloured earlywood is abrupt or more or Abnormalities occasionally occur in some less gradual depending on the year. It rarely trees during certain years, but these do not occurs in combination with a thin continu­ directly call the annual rhythm into question. ous band of marginal parenchyma. They mainly concern short periods of re­ duced growth during rainy seasons or the (text continued on page 128)

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Figs_ 1-5. Annual scars showing growth ring boundaries. - 1: Chlorophora excelsa. - 2: Triplochiton scleroxylon. - 3: Ajzelia ajricana. - 4: Entandrophragma angolense. - 5: Entandrophragma cylindricum.

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Figs. 6-9. Annual growth rings. - 6 & 7: Entandrophragma utile, x 1.5 & 7.7 respectively.- 8: Jacaranda copaia, x 14. - 9: Terminalia ivorensis, x 7.7.

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Figs. 10-13. Annual growth rings. - 10: Tectona grandis, x 7.7. -11: Chlorophora excelsa, x 7.7. - 12: Mansonia altissima, x 14. - 13: Pterocarpus soyauxii; the double arrow shows a false limit which is identical to a real annual boundary, x 7.7.

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No false rings or boundary duplication were but they can be misleading in a superficial observed in this species. The same does not study with the naked eye. hold true for Okoume, Aucoumea klaineana Well-marked boundaries of annual growth Pierre (Burseraceae), where the situation is rings are those delimited by marginal bands slightly different and more complex (Mariaux of parenchyma. These bands are easy to de­ 1970). The wood formed during a vegetative tect in species having mostly paratracheal or year comprises four different layers of fibres: apotracheal parenchyma in short bands. The a light one, then a dark layer composed of boundaries are sometimes not as easily de­ narrower fibres, then a second light layer and tectable when they appear in woods with at last a thin terminal dark layer. This pattern parenchyma throughout the growth ring in of annual growth rings is found in moder­ long bands or when the marginal parenchyma ately to fast growing trees. In trees growing band is discontinuous. Woods with continu­ more slowly the second light layer is some­ ous and distinct bands include species of times absent, and the dark terminal band is Entandrophragma, Meliaceae (Detienne & then fused with the first dark layer, or the Mariaux 1977), E. angolense C. DC. (Tiama, dark layer is reduced to a thin band resem­ Fig. 4), E. cylindricum Sprague (Sapelli, Fig. bling the terminal layer. Moreover, since the 5), E. utile Sprague (Sipo, Fig. 6), and a trunks of young Okoume are often fluted, the group of Leguminosae, A/zelia spp. (Dous­ rings are uneven: they are very thick in some sie), Andira coriacea Pulle (Saint Martin sectors, very thin or even absent elsewhere. rouge) and Pterocarpus soyauxii Taub. (Pa­ Among the other woods with sparse paren­ douk, Fig. 13). It is highly probable that the chyma, another member of the Burseraceae, same type of marginal band delimits annual Canarium schwein/urthii Engl. (Aiele), the rings in woods of other Entandrophragma Meliaceous Khaya anthotheca C. DC., Khaya species with sparse parenchyma (E. congo­ ivorensis A. Chev. (African mahogany) and ense A. Chev., E. spicatum Sprague, etc.), Lovoa trichilioides Harms (Dibetou), Goupi, of Swietenia spp., and of a number of genera Goupia glabra Aubl. of the Goupiaceae and of the Caesalpinioideae (Leguminosae), e. g. Grignon franc, Ocotea rubra Mez (Lauraceae) Brachystegia, Daniellia (Amobi1973), Deta­ show dark fibre zones of which the appear­ rium, Hymenaea, Macrolobium, Monopeta­ ance is sometimes underlined by a lower fre­ lanthus, Peltogyne, but this hypothesis needs quency of vessels. However, these bands are further experimental support. In A/zelia and not always clearly distinct and, moreover, Andira, the thin marginal band, even if it is others that are considered as false rings are sometimes occasionally interrupted, is always more or less frequent. In Ocotea rubra, the clearly visible and does not pose any inter­ orientation of the diagonal arrangement of pretation problems. False rings were not de­ vessels shows a certain periodicity, but the tected in either genus but their presence in change in orientation occurs several times a Padouk seems to be frequent enough so as to year. Thus, the accurate delimitation of an­ make the dating of the trees inaccurate be­ nual growth rings in these species cannot be cause of overestimation. Incomplete or mis­ expected. sing rings seem to be scarce; they have been Only few tropical woods, such as Teak, recorded in only one slow growing specimen Tectona grandis L.f. (Verbenaceae; Fig. 10) of Andira. The annual marginal band of En­ and American Cedro, Cedrela odorata L. tandrophragma can easily be detected because (Meliaceae) are semi-ring-porous and have it is continuous and straight in contrast to the rings visible to the naked eye: a thick band of other shorter and/or wavy bands occurring initial parenchyma partly including the wide within the annual rings of Sapelli and Sipo. earlywood vessels mark the ring boundary. Besides, this band is generally followed by a However, in some young fast growing thin zone of earlywood poor in vessels and Cedro, some very wide rings show bands parenchyma. No real false rings could be which are very rich in vessels alternating with observed in the 3 species of Entandrophrag­ zones where vessels are sparser. These varia­ ma, except for a few scarce bands of pa­ tions can easily be identified as false rings, renchyma comprising numerous vessels in

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Table 1. Annual growth ring features in some trees from tropical Africa and French Guiana.

., "'bO ~ ::t <) <) .5 '.:1i5·El -5-5 6 ~ ~ ~ ...0 ~~ . -5 "'0... c;~ 8~j :a ~ ~ ! > ~ ...... <) bOl .. 6 ·El ~l ::t Po] '" ;( s~ E'-"as .J. ~. 50£ S'il :9bO S"''O S lAM ·s a·S gj 'S Species ::t bO <) 6 ~ 'fa -5 ~ .D bO~ z·El £! CI) ~.£l u.s S >.=-.- u::..!l ~~ Araucariaceae Agathis moorei 2) (7) ± Bignoniaceae Jacaranda copaia (Fig. 8) 10 + 0 ± + Bursernceae Aucoumea klaineana 161 + + ± Canarium schweinfurthii (11) 0 Quyocaraceae Caryocar glabrum (5) ± 0 Clusiaceae Symphonia globulifera 8 0 0 ± ± ± Combretaceae Terminalia ivorensis (Fig. 9) 44 + + + Terminalia superba 219 + ± ± 0 + Goupiaceae Goupia g/abra (10) 0 L.aurarele Ocotea rubra (10) Legum.-Caesalpinioideae AJzelia sp. (Fig. 3) 32 0 + ± + Andira coriacea 10 + ± + Dicorynia guianensis 10 ± ± ± Legum.- Papilionoideae Pterocarpus soyauxii (Fig. 13) (19) ± 0 Meliaceae Cedrela odorata3) 10 + + ++ + Entandrophragma angolense (Fig. 4) 28 0 ++ 0 + Entandrophragma candollei 29 0 + ± ± Entandrophragma cylindricum (Fig. 5) 164 ± ++ + ± + Entandrophragma utile (Figs. 6, 7) 38 ± + + 0 + Guarea cedrata 23 0 0 + 0 ± Khayasp. (30) 0 Lovoa trichilioides (27) 0 0 Moraceae Chlorophora excelsa (Figs. I, 11) 70 ± ± ± ± + Myristicaceae Virola melinonii 10 + 0 + Sapotaceae Tieghemella heckelii 13 ± + + ± Simaroubaceae Simarouba omara 10 + ± + Sterculiaceae Mansonia altissima (Fig. 12) 49 ± ± ± 0 + Tarrietia utilis 44 ± ± ± ± Triplochiton scleroxylon (Fig. 2) 91 ± 0 ± ± Verbenaceae Tectona grandis 3) (Fig. 10) 14 ++ + ± + +

Legend: ++ =feature always present; + =generally present and distinct; ± =more or less present or distinct; see also 1); 0 =infrequent or not very distinct; - =absent 1) ± = depending on growth rate. - 2) New Caledonian species. - 3) Trees from plantations in Africa.

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Sapelli. In this species, the young suppressed Jacaranda copaia D. Don (Bignoniaceae, Fig. trees with little vigour may not fonn rings for 8), Iroko, Chlorophora excelsa Benth. & 1 year, or even 2 or 3 years running. The Hook. (Moraceae, Figs. 1, 11), Limba, Ter­ annual wounds enable the detection of these minalia superba Engl. & Diels (Combre­ missing rings: the earlier ring and the ring taceae) (Mariaux 1969; Rogers 1981), and formed after a year devoid of growth are Marupa, Simarouba amara Aubl. (Simarou­ separated by a nonnal band of parenchyma, baceae). Besides the narrow band of darker similar to that separating two consecutive an­ fibres characterising the end of the ring and nual rings. contrasting with the light earlywood, the In species with abundant parenchyma, in latewood often shows confluent parenchyma tangential bands, or paratracheal and conflu­ whilec the earlywood is characterised by a first ent, the annual growth rings are marked, but layer of wood with relatively low frequency are sometimes more difficult to delimit. In of vessels and shortly alifonn rather than Kosipo, Entandrophragma candollei Harms, confluent parenchyma. Occasionally in some Bosse, Guarea cedrata Pellegr. (Meliaceae), very wide growth rings, especially in Copaia Makore, Tieghemella heckelii Pierre (Sa­ and Limba, a band of parenchyma tangen­ potaceae), Angelique, Dicorynia guianensis tially links the first vessels of the earlywood. Amsh. (Caesalpinioideae, Leguminosae) and Because of its appearance and position in the Manil, Symphonia globulifera L. f. (Clusia­ earlywood it can never be considered as an ceae) , several variations converge towards initial band of a successive ring. It can never delimiting the annual rings. The thin marginal be associated with a false ring since, in Lim­ band of parenchyma is, if it exists, distinct ba as well as in Iroko, the actual growth ring from the other bands because it is straight and boundary is often traced by a thin, frag­ thin. When it is absent, especially in Ange­ mented tenninal band or by alifonn/con­ lique, the last band of parenchyma within the fluent parenchyma stretching into thinner and latewood generally tends to distinguish itself straighter wings that tend to line up tangen­ from the others thanks to its straight char­ tially. In these species, false rings, if present, acter. These boundaries can furthennore be are fairly easily recognisable as such: they located thanks to the difference in appearance often appear in the fonn of a band of darker of the parenchyma between the latewood and wood followed by lighter wood without any earlywood: the bands of parenchyma tend to abrupt transition as in the case of a true come closer towards the end of the growth annual boundary. These false rings generally ring, while the first zone of earlywood is occur only in one sector of the circumference. often characterised by less abundant pa­ Missing rings were rarely recorded in these renchyma, either in widely spaced or short species; on the other hand, wood fonnation bands or only vasicentric. The differences in can be nil for a year or two in one or several the fibre appearance are sometimes just as sectors of the circumference in a few trees distinct between the late- and earlywood. with eccentric growth or fluted trunk. However, despite all these features, detecting In Framire, Terminalia ivorensis A. Chev. annual growth rings is sometimes difficult in (Fig. 9) the narrow vasicentric parenchyma trees with very narrow rings, or when false does not show variations for locating annual rings are present. A thick continuous band of growth rings. The latter are generally clearly parenchyma sometimes observed throughout demarcated by an abrupt transition between the earlywood can easily be interpreted as a dark coloured latewood and light coloured false limit (rather frequent in Manil, occa­ earlywood. In medium and fast growing trees sional in Makore and other species). How­ it is usually easy to see the annual growth ever, false growth rings indistinct from real limits because they are directly succeeded by ones were detected in Kosipo. an initial zone poor in vessels that can be up Variations in appearance and abundance of t02mmwide. parenchyma generally enable the recognition The species studied with their parenchyma of annual growth boundaries in woods with mostly diffuse-in-aggregates, Bete, Mansonia mostly paratracheal parenchyma, e.g. Cop ala, altissima A. Chev. (Fig. 12), Niangon, Tarrie-

Downloaded from Brill.com10/01/2021 08:31:48AM via free access Detienne - Appearance and periodicity of growth rings in tropical woods 131 tia utilis Sprague (Detienne & Mariaux 1975), parenchyma. Missing growth rings or, con­ Samba, Triplochiton scleroxylon K. Sch. versely, duplicate boundaries may occur, but (Sterculiaceae; Fig. 2) (Lowe 1968; Detienne seem to be very scarce. Truly false growth & Mariaux 1976), and Chawari, Caryocar rings which cannot be differentiated from glabrum Pers. (Caryocaraceae), also show annual boundaries were not observed; on the annual variations of varying distinctness in other hand, parenchyma bands or a closer the appearance of their wood structure. The spacing of diffuse-in-aggregates parenchyma variation in colour between early- and late­ that may appear within an annual ring are wood is a rather adequate, although some­ generally misleading. times insufficient, character. In Chawari, parenchyma cells tend to assume a linear Conclusion arrangement in the latewood and form a ter­ Annual growth rings of tropical trees are minal, sometimes double, pseudo-band that usually marked by a variation in the wood is followed by a thin band devoid of paren­ structure, except in a small number of genera. chyma. However, in some trees or during These annual growth rings, whose appear­ certain periods in the life of a tree, this ance may differ according to genera are visi­ pseudo-band is not formed and the boun­ ble with a low power magnifying lens, some­ daries are blurred and difficult to make out times to the naked eye, and age determination from the false rings present in the form of of a specimen can often be achieved by a variations in the abundance of parenchyma. simple ring count. However, one should ac­ The growth rings of Niangon are just as knowledge that the age of a tropical tree can difficult to interpret. If the terminal pseudo­ be given only with some inaccuracy, due band formed by the alignment of cells and either to a slight overestimation caused by the diffuse-in-aggregates parenchyma is absent, presence of false rings not recognised as such the growth ring boundary is poorly marked or by an underestimation caused by missing and does not differ widely from false rings growth rings. formed by variations in abundance of pa­ Underestimation may also be caused by renchyma or vessels or by a more or less the difficulties in recognising the first growth continuous band of parenchyma. Growth rings, which may be poorly defined in the rings of Samba are often, although not al­ juvenile wood, formed when the tree experi­ ways, delimited by a continuous band of enced the shaded environment of the under­ parenchyma. Moreover, the ring boundary is story of the tropical rainforest. marked by an abrupt transition between dark­ coloured latewood, with thin diffuse-in­ References aggregates parenchyma, and light-coloured Alvim, P. 1964. Tree growth periodicity in earlywood, which starts either with a thin tropical climates. In: The formation of zone deprived of parenchyma or, in contrast, wood in forest trees (ed. M.H. Zimmer­ by a zone in which diffuse-in-aggregates mann): 479-495. Acad.Press,New York. parenchyma seems more abundant than in the Amobi, C.C. 1973. Periodicity of wood for­ latewood. False rings are sometimes formed mation in some trees of lowland rainforest by zones of parenchyma including numerous in Nigeria. Ann. Bot. 37: 211-218. vessels or by variations in the abundance Chowdhury, K.A. 1939. The formation of of parenchyma. In Bete (Fig. 12), although growth rings in Indian trees. Part I. Indian there are never any real marginal parenchyma For. Rec. (n. s.) II, no 1. bands, the boundary of each growth ring - 1940. The formation of growth rings in is marked by an abrupt difference between Indian trees. Part II. Indian For. Rec. the latewood in which fibres appear darker (n.s.) II, no 2 & 3. and the parenchyma aggregates are more Coster, Ch. 1927 & 1928. Zur Anatomie closely spaced, and the lighter-coloured ear­ und Physiologie der Zuwachszonen- und lywood with more widely spaced paren­ Jahresringbildung in den Tropen. Ann. chyma. In some growth rings, the earlywood Jard. Bot. Buitenzorg 37:49-160 & 38: starts with a thin zone poor in vessels and 1-114.

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Detienne, P. & C. Barbier. 1989. Rythmes Fay, E. de. 1986. Mode croissance cambiale de croissance de quelques essences de de quelques arbres tropicaux au stade Ouyane fran~aise. Bois et Forets des Tro­ juvenile. Naturalia Monspeliensia, n° hors piques no 217. In press. serie, Compte rendu du colloque inter­ - & A. Mariaux. 1975. Nature et periodicite national sur l'arbre: 13-27. des cernes dans Ie bois de Niangon. Bois Lowe, R.O. 1968. Periodicity of a tropical et Forets des Tropiques no. 159: 29-37. rain forest tree, Triplochiton scleroxylon - & - 1976. Nature et periodicite des cer­ K. Schum. Commonw. For. Rev. 47 (no. nes dans Ie bois de Samba. Bois et Forets 132): 150-163. des Tropiques no. 169: 29-35. Mariaux, A. 1969. La p6riodicite des cernes - & - 1977. Nature et periodicite des dans Ie bois de Limba. Bois et Forets des cernes dans les bois rouges de Meliacees Tropiques No. 128: 39-53. africaines. Bois et Forets des Tropiques - 1970. La periodicite de formation des No. 175: 52-61. cernes dans Ie bois de l'Okoume. Bois et Fahn, A. 1958. Xylem structure and annual Forets des Tropiques No. 131: 37-50. rhythm of development in trees and Rogers, S. 1981. Seasonal variation in radial shrubs of the desert. Trop. Woods 109: growth and phloem activity of Terminalia 81-94. ivorensis A.Chev. Ann. Bot. 47:603-610.

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