Cambial activity, growth ring analysis and wood density variability of planted teak (Tectona grandis L.f. (Lamiaceae)) in Ivory Coast

Although they currently absorb more carbon than they release, tropical forests suffer disturbances generated by human activities and amplified by global warming. Therefore, forest plantation, based on fast-growth fuelwood and timber species such as teak, becomes an option to counteract the risk of loss of these natural biomes. For its various advantages (ecological plasticity, good behaviour in plantation, fast-growth, high natural durability and wood density), teak (Tectona grandis) is introduced under different climatic conditions along the inter-tropical belt, occupying 75% of the world tropical timber plantations. However, this species remains highly sensitive to climate, suggesting that disturbances in the rainfall rate and intensity are expected to negatively affect tree growth and, consequently, induce variations in the derived wood properties. Therefore, to be successful, in response to the high demand for high quality wood, teak based reforestation programs should be underpinned with reliable and accurate information based on field data on tree growth rate and wood density dynamics. Because growth rate (reflected in ring widths) and wood density represent the main two functional traits that portray tree sensitivity/vylnerability to environment (climate). Information on the dynamics of growth and wood density remains, therefore, crucial to control and predict planted stands productivity, biomass estimate and the wood quality in regions marked by ongoing climatic variability like in Ivory Coast. Our study addressed the following questions: (i) What are the determining factors of wood formation and its fluctuations in teak planted in Ivory Coast? (ii) How does the precipitation variability influence managed and non managed tree growth? Is there a large-scale climatic signal in the tree growth rate (ring width), in addition to local the precipitation signal? (iii) How to assess the degree of variability of wood density in teak planted in Ivory Coast? Does climate variability affect teakwood density? To address these research questions, monthly cambial sampling was carried out in an evergreen forest and tree-ring analysis was performed in trees from 2 stands: a managed plantation located in an evergreen forest close to the Atlantic coast and an unmanaged semi-deciduous forest situated in the Central West Ivory Coast. Microdensity measurements were implemented on trees also from the evergreen forest, in order to assess the variations in wood density. Cambial activity showed that a 3 months dry season induced growth interruption and resulted in the formation of an annual xylem growth ring with 2 phloem rings over the same vegetative season. Anatomical quantification of the structural changes occurring in the cambial zone was closely correlated to monthly precipitations. Growth anomalies, induced by climatic and phenological variations during the growing period, were visualized through the formation of intra-annual xylem growth zones. Tree-ring analysis revealed higher growth rate in the managed trees than in the non-managed forest. In the deciduous forest, teak growth was only sensitive to the wet season precipitation while trees reacted to both wet and annual precipitation in the semi-deciduous forest. Anomalies in the sea surface temperature of the Gulf of Guinea also influenced trees growth. Moreover, growth patterns reflected the effect of three major El Niño events in the southern forest. Overall, climatic influence was more pronounced (slightly high correlation) in the non-managed teak plantation compared to the managed one as a consequence of the lack of sylvicultural intervention in the non-managed stand. This indicates the role of sylviculture in enabling trees to cope with a water deficit resulting from climate disturbances. The results reveal clear and direct effect of the broad-scale climate on tree growth, in addition to local precipitation recordings. Microdensitometrical profiling revealed that wood density was more variable within the tree than between trees. Intra-tree density variations reflected fluctuations occurring in the intra-ring xylem anatomy. Direct and significant correlations were found between October rainfall and the total ring wood density (r= 0.37; p<0.05) and latewood density (r= 0.41; p<0.05) which also correlated with the post-wet season rainfall (r=0.47; p< 0.05). The intra-ring anatomy related density changes led to the occurrence of the alternating pattern of intra-ring denstiy variation which best supported the correlation with the bimodal monthly precipitation. Inter and intra-annual density variations were high and persistent in the mature wood portion, indicating that the cambial age was not the main driving factor of the density variability. This research work, founded on original field data and unique for this region, provides highly useful results for teak plantations management in West-Africa. This scientific data evidences the sensitivity of teak growth to climate at both local and global scales. As a result of this climate sensitivity, (1) growth slowed down during years of low precipitation and (2) in response to intra-annual precipitations disturbances, trees formed intra-ring anatomy fluctuations which, in turn, result in the intra-ring density variations, the main source of the mean tree density variability. As a perspective to future research, a weekly cambial sampling could test the hypothesis on the intra-annual xylem growth zones formation which affected tree-ring density and, consequently, mean tree density. Monitoring of thinnings and pruning operations, combined with tree-ring analysis, and the monitoring of leaf area index, evapotranspiration and soil water content, could be a key to unravel the mechanism through which the managed stand trees adapt to water deficits. Heritability study could allow to establish the degree of the genetic control on wood density namely the earlywood features which could contribute to stabilize the mean tree wood density

Fluctuations of cambial activity in relation to precipitation result in annual rings and intra-annual growth zones of xylem and phloem in teak (Tectona grandis) in Ivory Coast

Background and Aims : Teak forms xylem rings that potentially carry records of carbon sequestration and climate in the tropics. These records are only useful when the structural variations of tree rings and their periodicity of formation are known. Methods : The seasonality of ring formation in mature teak trees was examined via correlative analysis of cambial activity, xylem and phloem formation, and climate throughout 1·5 years. Xylem and phloem differentiation were visualized by light microscopy and scanning electron microscopy. Key Results : A 3 month dry season resulted in semi-deciduousness, cambial dormancy and formation of annual xylem growth rings (AXGRs). Intra-annual xylem and phloem growth was characterized by variable intensity. Morphometric features of cambium such as cambium thickness and differentiating xylem layers were positively correlated. Cambium thickness was strongly correlated with monthly rainfall (R2 = 0·7535). In all sampled trees, xylem growth zones (XGZs) were formed within the AXGRs during the seasonal development of new foliage. When trees achieved full leaf, the xylem in the new XGZs appeared completely differentiated and functional for water transport. Two phloem growth rings were formed in one growing season. Conclusions : The seasonal formation pattern and microstructure of teak xylem suggest that AXGRs and XGZs can be used as proxies for analyses of the tree history and climate at annual and intra-annual resolution

Tree rings show a different climatic response in a managed and a non-managed plantation of teak (Tectona grandis) in West Africa

Establishing large-scale plantations of teak could reduce the pressure on natural forests and sequester atmospheric carbon into durable wood. Understanding the growth dynamics of this species in plantations, outside its natural distribution area, is crucial for forest management. Stem discs of teak were collected in Ivory Coast at two sites, a non-managed plantation (Gagnoa) and a managed plantation (Seguie). All stem discs were processed using the standard dendrochronological methods in order to unravel the relationships between growth and climate. Results showed that growth is slower in Gagnoa compared to the Seguie plantation that is being thinned regularly. In Gagnoa, trees responded positively to April rainfall, i.e., during the early stage of tree-ring formation, and negatively to September-October rainfall, i.e., during the short dry period. In Sgu, trees responded positively to July rainfall, i.e., during latewood formation, under decreasing rainfall. At both sites, tree growth was influenced by sea-surface temperature anomalies during the summer in the Gulf of Guinea. Teak growth in Sauie could be additionally linked to El Nino events, specifically during three major episodes (1976-77, 1982-83 and 1997-98)

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. 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

Clinical and genetic characteristics of late-onset Huntington's disease

Background: The frequency of late-onset Huntington's disease (&gt;59 years) is assumed to be low and the clinical course milder. However, previous literature on late-onset disease is scarce and inconclusive. Objective: Our aim is to study clinical characteristics of late-onset compared to common-onset HD patients in a large cohort of HD patients from the Registry database. Methods: Participants with late- and common-onset (30–50 years)were compared for first clinical symptoms, disease progression, CAG repeat size and family history. Participants with a missing CAG repeat size, a repeat size of ≤35 or a UHDRS motor score of ≤5 were excluded. Results: Of 6007 eligible participants, 687 had late-onset (11.4%) and 3216 (53.5%) common-onset HD. Late-onset (n = 577) had significantly more gait and balance problems as first symptom compared to common-onset (n = 2408) (P &lt;.001). Overall motor and cognitive performance (P &lt;.001) were worse, however only disease motor progression was slower (coefficient, −0.58; SE 0.16; P &lt;.001) compared to the common-onset group. Repeat size was significantly lower in the late-onset (n = 40.8; SD 1.6) compared to common-onset (n = 44.4; SD 2.8) (P &lt;.001). Fewer late-onset patients (n = 451) had a positive family history compared to common-onset (n = 2940) (P &lt;.001). Conclusions: Late-onset patients present more frequently with gait and balance problems as first symptom, and disease progression is not milder compared to common-onset HD patients apart from motor progression. The family history is likely to be negative, which might make diagnosing HD more difficult in this population. However, the balance and gait problems might be helpful in diagnosing HD in elderly patients