Growth-Ring Distinctness and Boundary Anatomy Variability in Tropical Trees

Abstract

The phenomenon of distinct, absent or indistinct growth rings is a highly variable feature used for wood identification and a wide range of tree-ring studies. Causes for its variability are not yet fully understood. There is also a lack of consensus within the scientific community about how distinct and indistinct tree rings should be defined and classified. We use a selection of 103 Central African rainforest trees to analyse the anatomy of growth-ring boundaries of 103 Central African rainforest species and assessed the influence of the climate, tree organ and leaf shedding behaviour on growth-ring distinctness and anatomy. We observed a high variability of tree-ring boundaries anatomy and distinctness within and among individuals and species. Although, for some semi-deciduous species, higher incidence of distinct growth rings appears to be related with a more pronounced seasonal climate, no general trends are observed for the assembly of studied species. Growth rings are variable within individuals depending on the considered organ: trunks tend to show more distinct rings than branches. Growth-ring distinctness is difficult to implement as a trait to measure tree performance when only based on abrupt changes in fibre size and cell wall thickness. From the potential growth-ring markers identified in the IAWA list of hardwood features, those applying to vessel and parenchyma density and distended rays appear to be more useful in tropical trees than abruptly flattened latewood fibres or abrupt changes in vessel diameter.

The growth ring concept: seeking a broader and unambiguous approach covering tropical species

“…The study of growth rings in the tropics is much more complex than in temperate regions due to the greater number of species, diversity of habitats, behaviour of cambial activity and phenology, anatomical markers for growth rings and their respective degrees of distinction and mainly the absence of well‐defined seasons (Borchert, ; Borchert & Rivera, ; Schöngart et al ., ; Worbes & Fichtler, ; Slik et al ., ; Tarelkin et al ., ; Silva et al ., ; Islam, Rahman & Bräuning, ). It is not only the high species diversity of tropical regions which contributes to the greater structural variability of growth rings (Worbes & Fichtler, ) but also the greater complexity of the secondary xylem of the angiosperm species which dominate these environments, as compared to that of the gymnosperms (Wheeler, Baas & Gasson, ; Carlquist, ; Evert, ).…”

Tree Growth Rings in Tropical Peat Swamp Forests of Kalimantan, Indonesia

“…In studies of Malaysian forests, a lack of rings or the prevailing of indistinct rings are mentioned [39][40][41], and the same is reported for India (e.g., [42]), based on the interpretation of wood anatomical slides alone. In a recent study of Congo timber using wood anatomical properties, 40% of the evergreen species from moist forests were classified into the group of trees with distinct rings [26]. For the Indonesian islands, besides Java, tree ring studies are completely lacking.…”

“…Distinct growth zones are those with a clear density differentiation into early wood and late wood, a clear anatomical structure at the ring boundaries such as marginal parenchyma bands, ring-like unequally distributed vessels, or a re-occurring pattern of parenchyma and fiber bands [8,15,26] (e.g., Horsfieldia crassifolia). When classified as distinct, the structures should be visible over the entire stem disc, at least outside the center where the structure of the juvenile wood often slightly deviates from mature wood [9].…”

Diversidade florística, dendrologia e dendroecologia em florestas estacionais decíduas do Centro e Norte do Peru

“…Os anéis de crescimento das árvores tropicais podem ser distintos, indistintos ou ausentes, no entanto, com todas as variações nos limites das camadas é preciso definir melhor essas características, no entanto, há também uma falta de consenso na comunidade científica sobre como anéis de árvore distintos e indistintos devem ser definidos e classificados (Tarelkin et al, 2016). Os anéis de crescimento das árvores tropicais quando estão presentes podem estar delimitados por (a) fibras de paredes espessas e radialmente achatadas no lenho tardio versus fibras no lenho inicial de paredes finas, (b) acentuadas diferenças no diâmetro dos vasos entre o lenho tardio e lenho inicial do seguinte anel, (c) parênquima marginal (d) elementos vasculares muito estreitos e numerosos ou formando o tecido principal do lenho tardio e ausência do lenho inicial (e) decrescimento da frequência das bandas de parênquima em direção ao lenho tardio resultando em zonas de fibras distintas e (f) raios distendidos .…”

“…258). Existe posições contrastantes com respecto ao significado da palavra anéis distintos na delimitação das camadas de crescimento , também considero que é vago e arbitrário e sua abordagem deve ser mais flexível na classificação dos anéis de crescimento Tarelkin et al, 2016). Categorias de classificação de anéis distinto ou indistinto no nível macroscópico (ao olho nú ou só com ajuda de estéreo microscópio de 10 a 40 x), que pode se incluir em outros estudos de caracterização de anéis de crescimento são: (1) Alta distinção dos anéis de crescimento, indica se quando os limites dos anéis de crescimento são claramente visíveis a olho nu, apresentam cores homogêneas no raio total do lenho, têm contrastes das cores entre os anéis e seus limites, apresentam vasos que variam em densidade no lenho inicial e no lenho tardio, ou o parênquima axial paratraqueal tem um arranjo diferente entre os anéis; (2) boa distinção, indica se quando os limites dos anéis são visíveis a olho nu, mas variam em espessura e cor (de intenso a tênue ou vice-versa), não tem um padrão homogêneo.…”