X-ray tomography as a tool for detailed anatomical analysis

Bulcke, Jan Van den; Boone, Matthieu N.; Acker, Joris Van; Stevens, Marc; Hoorebeke, Luc Van

doi:10.1051/forest/2009033

Cited by 72 publications

(21 citation statements)

References 25 publications

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“…An example fragment per charcoal type was chosen for detailed visualization using scanning electron microscopy and laboratory‐based high‐resolution X‐ray CT (Van den Bulcke et al ., ; Hubau et al ., ,b) for detailed anatomical description using well‐defined features (IAWA Committee, ; Wheeler, ). Each charcoal type was identified using a recently developed protocol (for a detailed discussion, see Hubau et al ., ) using a database of more than 2900 woody species.…”

Section: Methodsmentioning

confidence: 99%

Charcoal‐inferred Holocene fire and vegetation history linked to drought periods in the Democratic Republic of Congo

Hubau

Bulcke

Acker

et al. 2015

Global Change Biology

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The impact of Holocene drought events on the presumably stable Central African rainforest remains largely unexplored, in particular the significance of fire. High-quality sedimentary archives are scarce, and palynological records mostly integrate over large regional scales subject to different fire regimes. Here, we demonstrate a direct temporal link between Holocene droughts, palaeofire and vegetation change within present-day Central African rainforest, using records of identified charcoal fragments extracted from soil in the southern Mayumbe forest (Democratic Republic of Congo). We find three distinct periods of local palaeofire occurrence: 7.8-6.8 ka BP, 2.3-1.5 ka BP, 0.8 ka BP - present. These periods are linked to well-known Holocene drought anomalies: the 8.2 ka BP event, the 3rd millennium BP rainforest crisis and the Mediaeval Climate Anomaly. During and after these Holocene droughts, the Central African rainforest landscape was characterized by a fragmented pattern with fire-prone open patches. Some fires occurred during the drought anomalies although most fires seem to lag behind them, which suggests that the open patches remained fire-prone after the actual climate anomalies. Charcoal identifications indicate that mature rainforest patches did persist through the Early to Mid-Holocene climatic transition, the subsequent Holocene thermal optimum and the third millennium BP rainforest crisis, until 0.8 ka BP. However, disturbance and fragmentation were probably more prominent near the boundary of the southern Mayumbe forest. Furthermore, the dominance of pioneer and woodland savanna taxa in younger charcoal assemblages indicates that rainforest regeneration was hampered by increasingly severe drought conditions after 0.8 ka BP. These results support the notion of a dynamic forest ecosystem at multicentury time scales across the Central African rainforest.

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Section: Methodsmentioning

confidence: 99%

Charcoal‐inferred Holocene fire and vegetation history linked to drought periods in the Democratic Republic of Congo

Hubau

Bulcke

Acker

et al. 2015

Global Change Biology

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“…If these markers repeat periodically in the direction of the wood's radial growth, there is less doubt as to the presence or absence of growth rings. Chemical (Gourlay, ; Poussart, Evans & Schrag, ) and physical assays (Worbes, ; van den Bulcke et al ., ; Bastin et al ., ) have been proposed and although valid in many cases, they may not apply in others (Pagotto et al ., ), and still do not eliminate subjectivity and are very costly. The degree of distinction of growth rings may vary with the magnification at which the wood is observed.…”

Section: Anatomical Featuresmentioning

confidence: 98%

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

2019

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The concept of growth rings is little discussed in the literature and their treatment remains somewhat confusing in terms of the diversity of structures described. This situation has a major impact on the study of growth rings in tropical species, in which variations and complexity are greater and accuracy of identification less good. The rigid conceptual delimitations used by dendrochronologists and wood anatomists of temperate regions cannot be applied to the study of growth rings in most tropical species, which has led to neglect of this subject. With the objective of discussing the concept of growth rings, the present study consists of a survey of anatomical, periodicity, causal and evolutionary aspects of the treatment of these structures as evidenced in previous studies, and the evaluation of their application and limitations to the development of this concept. Anatomical aspects arise through radial integrity, or the presence of early and late wood; the degree of distinction of the rings, which may vary from well to poorly defined; and tangential continuity, meaning that rings may form a complete circle in the transverse section of the trunk, or instead be tangentially discontinuous, lens-shaped or in wedges. In addition there are a diversity of anatomical markers which enable us to recognize growth rings. Regarding periodicity, the rings may be annual, infra-annual or supra-annual. Causal aspects include genetic, endogenous and environmental components. Evolutionary aspects continue to be insufficiently investigated, and although most comparative studies treat growth rings recognized by different markers as though they were a single character, it remains questionable whether they can be regarded as homologous or the result of homoplasy. We conclude that the elaboration of a robust but broad definition which can include all the variation observed in growth rings of tropical species is a complex task, which is only possible by overcoming the restrictions adopted by dendrochronologists and wood anatomists of temperate regions for whom growth rings are essentially annual, strongly demarcated, tangentially continuous and restricted to the most pronounced markers.

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“…High-resolution densitometry can be obtained with blue intensity [7] or X-ray densitometry [8] systems that combine densitometry with anatomical observations [9,10], and many other devices exist as well [11]. X-ray Computed Tomography (CT) microdensitometry is a technique that allows obtaining 3D density volumes, that can be converted to large datasets of density profiles [12,13], with resolution ranging from submicron level [14] to coarser resolutions to perform tree-ring analysis [15,16]. Maximum latewood density of conifers is next to tree-ring width one of the parameters used to, for instance, reconstruct summer temperature [17], and earlywood is being explored as well [18].…”

Section: Introductionmentioning

confidence: 99%

Wood Density Profiles and Their Corresponding Tissue Fractions in Tropical Angiosperm Trees

Mil

Tarelkin

Hahn

et al. 2018

Forests

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Wood density profiles reveal a tree’s life strategy and growth. Density profiles are, however, rarely defined in terms of tissue fractions for wood of tropical angiosperm trees. Here, we aim at linking these fractions to corresponding density profiles of tropical trees from the Congo Basin. Cores of 8 tree species were scanned with X-ray Computed Tomography to calculate density profiles. Then, cores were sanded and the outermost 3 cm were used to semi-automatically measure vessel lumen, parenchyma and fibre fractions using the Weka segmentation tool in ImageJ. Fibre wall and lumen widths were measured using a newly developed semi-automated method. An assessment of density variation in function of growth ring boundary detection is done. A mixed regression model estimated the relative contribution of each trait to the density, with a species effect on slope and intercept of the regression. Position-dependent correlations were made between the fractions and the corresponding wood density profile. On average, density profile variation mostly reflects variations in fibre lumen and wall fractions, but these are species- and position-dependent: on some positions, parenchyma and vessels have a more pronounced effect on density. The model linking density to traits explains 92% of the variation, with 65% of the density profile variation attributed to the three measured traits. The remaining 27% is explained by species as a random effect. There is a clear variation between trees and within trees that have implications for interpreting density profiles in angiosperm trees: the exact driving anatomical fraction behind every density value will depend on the position within the core. The underlying function of density will thus vary accordingly.

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X-ray tomography as a tool for detailed anatomical analysis

Cited by 72 publications

References 25 publications

Charcoal‐inferred Holocene fire and vegetation history linked to drought periods in the Democratic Republic of Congo

Charcoal‐inferred Holocene fire and vegetation history linked to drought periods in the Democratic Republic of Congo

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

Wood Density Profiles and Their Corresponding Tissue Fractions in Tropical Angiosperm Trees

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