Papers by Maaike De Ridder
Les déterminants de la croissance de Triplochiton scleroxylon and les implications pour la gestion forestière en Afrique centrale
The sustainability of the polycyclic logging system in tropical forests has been increasingly que... more The sustainability of the polycyclic logging system in tropical forests has been increasingly questioned for a variety of reasons, and particularly in central Africa as commercial species, mostly light-demanding long-lived pioneer species, usually fail to recover a stable number of large trees after exploitation. Several factors are known to affect tropical tree demographic processes, like tree growth, survival and recruitment. Tree growth has particularly been showed to depend on ecological conditions, tree genetics, and competition with surrounding vegetation, as well as tree size or ontogeny. Yet, due to the paucity of available data, the importance of such factors is unclear and usually ignored when estimating future timber yields. To fill this gap, we chose to evaluate the variability in growth of one African long-lived pioneer and commercially very important species: Triplochiton scleroxylon K. Schum, gathering a broad dataset composed of tree ring data recorded in one site in...
Analyse van de brandhout- en houtskoolkwaliteit van Acacia auriculiformis, Acacia mangium en hun hybride in het Luki-reservaat (DRC)
Submitted in <b>2010</b>, 2010
Contributing to wood anatomical databases to improve species identification, phylogeny and functional trait research in Central Africa
The long-lived pioneer species Pericopsis elata is one of the rare tropical timbers on the list o... more The long-lived pioneer species Pericopsis elata is one of the rare tropical timbers on the list of the Convention on International Trade of Endangered Species, supporting the need for accurate and reliable growth data. In one planted and one natural forest in the Democratic Republic of Congo, respectively four and 37 Pericopsis stem disks were collected. The tree-ring series of planted trees were used to confirm annual tree-ring formation. For the natural forest, a tree-ring chronology with 24 stem disks ranged from 1852 up to 2008. This chronology was compared with time-series of local precipitation, resulting in a significant correlation with the second half of the rainy season (September-November). This seasonal precipitation was related with sea surface temperatures of the West Indian Ocean. Higher precipitation during El Niño years corresponded with higher tree-ring indices but differences were not significant. In addition, pointer years were rare and did not have a consistent link with extreme climatic conditions. The existence of annual tree rings encourages further tree-ring analyses of P. elata and other flagship timber species in order to further document climate-growth responses and to provide the long-term framework that is needed for sustainable management planning.
In the heart of the limba tree (Terminalia superba Engl. & Diels): detection methods for heart rot
and false heartwood
Background: The identification of tropical African wood species based on microscopic imagery is a... more Background: The identification of tropical African wood species based on microscopic imagery is a challenging problem due to the heterogeneous nature of the composition of wood combined with the vast number of candidate species. Image classification methods that rely on machine learning can facilitate this identification, provided that sufficient training material is available. Despite the fact that the three main anatomical sections contain information that is relevant for species identification, current methods only rely on the transversal section. Additionally, commonly used procedures for evaluating the performance of these methods neglect the fact that multiple images often originate from the same tree, leading to an overly optimistic estimate of the performance. Results: We introduce a new image dataset containing microscopic images of the three main anatomical sections of 77 Congolese wood species. A dedicated multiview image classification method is developed and obtains an ...
Methodology to use xylarium specimens to generate wood technological output
Databases and code for the publication entitled: "Growth determinants of timber species Triplochiton scleroxylon and implications for forest management in central Africa
This archive contains all the necessary data and R script to reproduce the results of the manuscr... more This archive contains all the necessary data and R script to reproduce the results of the manuscript entitled "Growth determinants of timber species Triplochiton scleroxylon and implications for forest management in central Africa" published in Forest Ecology and Management. It includes database csv files, script to reproduce the main analyses and figures with R software and documentation. ayous_growth : measures of ayous diameter id : measurement id id_tree : tree id id_plot : plot id date : measurement date diameter : measured diameter (cm) hom : heaight of point of measure (cm) year : census year code_observation : observation codes (see dico_src.xls, multiple codes can be used) code_mortality : mortality codes (see dico_src.xls) comment : additionnal comments recorded in the field valid_hom_obs : TRUE = no change in hom over time / FALSE = hom changed over time not_identified_error : TRUE = no error / FALSE = an erroneous data data was identified for this tree ayous_pl...
Sustainable forest management primarily depends on the availability of quantitative data, often n... more Sustainable forest management primarily depends on the availability of quantitative data, often not available in tropical forests. The lack of long-term data on tree growth, wood production and carbon stocks hampers the implementation of sustainable forest management and possible financing by Kyoto Protocol related tools like REDD+ and Clean Development Mechanisms. Africa is the continent with the lowest percentage of sustainably managed forests and especially African rainforests are currently poorly sampled. Data on wood production and carbon stocks can be collected in several ways but mostly originate from large-scale inventories or repeated measurements of permanent sample plots. These methods are time- and labour-intensive in tropical forests. Moreover, the inventory data require a temporal scale that enables long-term planning. Measurements of carbon stock include the weighing of aboveground biomass of complete trees. Pantropical models are based on these destructive measuremen...
The Tervuren xylarium and wood biology to decode the ecological memory of forests and trees
The EGU General Assembly, 2014
DHXCT: the use of helical X-ray CT in dendro-research
X-ray Computed Tomography (XCT) has become a well-established technique in many fields of science... more X-ray Computed Tomography (XCT) has become a well-established technique in many fields of science. Its application in wood research is also increasing considerably. Thanks to the non-destructive nature of the imaging process as well as the internal view on the three-dimensional structure, it is one of the pre-eminent techniques for multi-scale studies of wood. With standard cone-beam tomography, however, long samples with limited cross-sectional dimensions are hard to scan at high resolution. Stacked scanning and volume stitching are necessary for such samples. Tree-ring research mainly uses increment cores or generally speaking pith-to-bark trajectories which are typically long but with rather small cross-sectional dimensions. Such samples, therefore, could benefit from other acquisition routines, such as the helical scanning protocol. The sample is not only rotated 360° but is also moved along the z-axis, resulting in a helical movement. We will show how helical X-CT (HXCT) can be of use in tree-ring research, giving examples of its use on oak (Quercus spp.), limba (Terminalia superba) and teak (Tectona grandis). Custom-made sample holders enable scanning of several pith-to-bark trajectories sawn from wood disks simultaneously. Reconstructed volumes can be converted to absolute densities without classical time-consuming calibration methods and density profiles can be obtained. Furthermore, the 3D volume can also be used for accurate ring width measurements taking into account ring and grain angle. In some cases, quantitative wood anatomical measurements are also feasible. Finally, dedicated scans at higher resolution can resolve finer anatomical details.
Annals of Botany, 2011
† Background and Aims Density is a crucial variable in forest and wood science and is evaluated b... more † Background and Aims Density is a crucial variable in forest and wood science and is evaluated by a multitude of methods. Direct gravimetric methods are mostly destructive and time-consuming. Therefore, faster and semito non-destructive indirect methods have been developed. † Methods Profiles of wood density variations with a resolution of approx. 50 mm were derived from one-dimensional resistance drillings, two-dimensional neutron scans, and three-dimensional neutron and X-ray scans. All methods were applied on Terminalia superba Engl. & Diels, an African pioneer species which sometimes exhibits a brown heart (limba noir). † Key Results The use of X-ray tomography combined with a reference material permitted direct estimates of wood density. These X-ray-derived densities overestimated gravimetrically determined densities non-significantly and showed high correlation (linear regression, R 2 ¼ 0. 995). When comparing X-ray densities with the attenuation coefficients of neutron scans and the amplitude of drilling resistance, a significant linear relation was found with the neutron attenuation coefficient (R 2 ¼ 0. 986) yet a weak relation with drilling resistance (R 2 ¼ 0. 243). When density patterns are compared, all three methods are capable of revealing the same trends. Differences are mainly due to the orientation of tree rings and the different characteristics of the indirect methods. † Conclusions High-resolution X-ray computed tomography is a promising technique for research on wood cores and will be explored further on other temperate and tropical species. Further study on limba noir is necessary to reveal the causes of density variations and to determine how resistance drillings can be further refined.
Review of Palaeobotany and Palynology, 2012
Direct evidence for Central African vegetation history is mostly derived from palynology and pala... more Direct evidence for Central African vegetation history is mostly derived from palynology and palaeolimnology. Although anthracology has proven worthwhile for palaeovegetation reconstructions in temperate regions and South America, charcoal analysis has hardly been applied for Central Africa. Moreover, a transparent charcoal identification procedure using large databases and well defined characters has never been developed. Therefore, we present a Central African charcoal identification protocol within an umbrella database of species names and metadata, compiled from an on-line database of wood-anatomical descriptions (InsideWood), the database of the world's largest reference collection of Central African wood specimens (RMCA, Tervuren, Belgium) and inventory and indicator species lists. The 2909 Central African woody species covered by this database represent a large fraction of the total woody species richness of Central Africa. The database enables a directed search taking into account metadata on (1) anatomical features, (2) availability of thin sections within the reference collection, (3) species distribution and (4) synonymy. The protocol starts with an anatomical query within this database, focussing on genus rather than species level, proceeds with automatic extension and reduction phases of the resulting species list and ends with a comparative microscopic study of wood reference thin sections and charcoal anatomy. In total, 76.2% of the Central African species in the database are taken into consideration, focussing on indicator and inventory species. The protocol has a large geographical applicability, as it can be optimised for every research area within Central Africa. Specifically, the protocol has been optimised for the Mayumbe region and applied to radiocarbon dated (2055-2205 14 C yr BP) charcoal collections from a pedoanthracological excavation. The validity of the protocol has been proven by the mutual consistency of charcoal identification results and the consistency of these identification results with vegetation history based on phytogeographical and palynological research within and around the Mayumbe. As such, anthracology complements palynology and a combination of both can lead to stronger palaeobotanical reconstructions.
Forest Ecology and Management, 2013
Improved forest management in the tropics is hampered by the limited availability of quantitative... more Improved forest management in the tropics is hampered by the limited availability of quantitative data, especially in tropical Africa. Important management parameters such as the minimum logging diameter (MLD), the associated biological rotation age (BRA) and the timing of silvicultural treatments are too often based on merchantable dimensions and state regulations instead of ecological data and tree growth. This study combines inventory data and bootstrapped tree-ring curves of natural and planted trees of the long-lived pioneer species Terminalia superba Engl. & Diels. A growth-oriented MLD was calculated, and the need and timing of silvicultural treatments was estimated based on the analysis of growth releases and suppressions. Study sites were situated in the Congolese Mayombe forest and western Ivory Coast. Tree rings from 41 natural forest trees (stem discs) and 29 plantation trees (increment cores) were measured, along with diameter and height measurements. Planted and natural forests showed considerable differences in mean growth rate and growth curves. More than 50% of the trees nevertheless reached the canopy without growth releases or suppressions, confirming that T. superba does not require intensive management. The growth-oriented MLD not only differs considerably between sites but bootstrapping revealed large differences within forest regions/types. Furthermore, volume-based MLD and BRA are on average larger than basal area-based calculations. The modified monocyclic management system is suggested, especially for planted forests with light-demanding, fast-growing tree species. One small-scale thinning during the juvenile phase is recommended before a final harvest that includes all trees above the growth-oriented MLD. The introduction of sustainable management for T. superba therefore primarily depends on forest type and cannot be generalized at the species level.
Annals of Forest Science, 2010
In the 1940s-1950s, large limba (Terminalia superba Engl. & Diels) plantations were established i... more In the 1940s-1950s, large limba (Terminalia superba Engl. & Diels) plantations were established in the Democratic Republic of Congo to reduce the pressure on the natural forests. • The objective of this study was to evaluate the potential of these long-rotation plantations as production forests (timber) and carbon sinks. • Five different plantations, between 50 and 58 years old, were sampled. Over a sample surface of more than 73 ha, the diameter above buttresses of 2 680 trees, bole height of 265 trees and tree height of 128 trees was measured. • To estimate the commercial volume, a nonlinear power law regression was used (R 2 = 0.95). A power law variance function was applied to counter heteroscedasticity of the residual plot. Estimates of commercial tree and stand volume at 50 to 58 y were 5.6 ± 4.1 m 3 and 183.9 ± 135.0 m 3 ha −1. Stand volumes appear low but are explained by a large decrease in tree density. However, the mean volume increment of 3.2-3.7 m 3 ha −1 y −1 corresponds well with teak plantations of a similar age. For limba, aboveground biomass and carbon estimates of this study (resp. 108.4 and 54.2 Mg ha −1) differ significantly from those of existing aboveground biomass models (resp. 135.7-143.9 Mg ha −1 biomass and 67.9-72.0 Mg ha −1 C). All aboveground biomass and carbon estimates for T. superba stands were lower than for the estimates of young fast-growing plantations like Tectona grandis L. f., Eucalyptus spp. and Acacia spp. (≤ 30 y). Mots-clés : Terminalia superba / Afrique centrale / plantation / volume / biomasse Résumé-Le potentiel des plantations de Terminalia superba Engl. & Diels dans la production de bois et de biomasse (forêt de Mayombe, République Démocratique du Congo). • Dans les années 1940-1950, de grandes plantations de limba (Terminalia superba Engl. & Diels) on été mises en place en République Démocratique du Congo afin de réduire la pression sur les forêts naturelles. • L'objectif de cette étude était d'évaluer le potentiel de ces plantations anciennes comme forêts de production de bois d'oeuvre et puits de carbone. • Cinq plantations différentes, âgées de 50 à 58 ans, ont été échantillonnées. Sur une surface de plus de 73 ha, le diamètre au-dessus des contreforts de 2 680 arbres, la hauteur de fût de 265 arbres et la hauteur totale de 128 arbres ont été mesurés. • Le volume commercial a été estimé à l'aide d'une régression du type loi de puissance (R 2 = 0.95). Une fonction de variance du même type a été adoptée pour supprimer l'hétéroscedasticité des résidus. Le volume commercial a été estimé à 5.6 ± 4.1 m 3 par arbre et 183.9 ± 135.0 m 3 ha −1. Ce dernier volume semble faible mais peut être expliqué par une chute de la densité d'arbres. Toutefois, l'accroissement moyen en volume (3,2-3,7 m 3 ha −1 an −1) correspond bien avec des plantations de teck d'un âge comparable. Pour le limba, il y a une différence significative entre les valeurs d'estimation de biomasse et de quantité de carbone épigés dans cette étude (resp. 108,4 Mg ha −1 et 54,2 Mg ha −1) et dans les modèles existants (resp. 135,7-143,9 Mg ha −1 et 67,9-72,0 Mg ha −1 C). Ces estimations de biomasse et de quantité de carbone épigés pour T. superba sont également inférieures à celles de jeunes plantations d'espèces à croissance rapide comme Tectona grandis L. f., Eucalyptus spp. and Acacia spp. (≤ 30 ans). * This study was performed at the two institutions but Ghent University is the main institution.
TRACE-Tree Rings in Archaeology, Climatology and Ecology, 2007
The uptake of heavy metals is assumed to be a possible limiting factor for tree growth. In additi... more The uptake of heavy metals is assumed to be a possible limiting factor for tree growth. In addition, it may also induce toxic effects. In the past, several studies have been conducted on the effect of industrial emissions on the growth of trees and the fixation of heavy metals in their wood (eg Baes & McLaughlin 1984, Stoeckhardt 1871 & Bakke 1913 in Cook & Kairiukstis 1990). Unfortunately, the results of this research are often contradictory. Furthermore, the past studies were mainly based on American tree species (USA) while ...
Van den Bulcke, J., Van Loo, D., Dierick, M., Boone, M., Masschaele, B., De Witte, Y., Haneca, K.... more Van den Bulcke, J., Van Loo, D., Dierick, M., Boone, M., Masschaele, B., De Witte, Y., Haneca, K., et al.(2011). Multi-resolution X-ray tomography for multi-purpose use in cultural heritage. COST Actions IE0601 and MP0601, Joint final conference, Proceedings (pp. 55–57). Presented at the Joint final conference of COST Actions IE0601 and MP0601.
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Papers by Maaike De Ridder