Diversity in specific gravity and water content of wood among Bornean tropical rainforest trees

Wood properties were measured for trees in lowland dipterocarp forests in West Kalimantan. In 1993 and 1994, 353 samples of 286 species were collected from trunk base of trees of approximately 5 cm in diameter, and the specific gravities (SG: oven dry weight/fresh volume) and water contents of wood including bark were measured. The SG of each species ranged from 0.21 to 0.84, and the mean ± SD was 0.53 ± 0.13. The wide range of SG suggests that the forest had a high diversity in wood properties. The most dominant and diversified genus in this area was Shorea, and the SG of 15 species varied from 0.21 to 0.71. The range covered SG of pioneer (six Macaranga, 0.29–0.43) and small trees in primary forests (nine Eugenia and 10 Xanthophyllum, 0.55–0.77). The SG average for tree species of secondary forests of 2–6 years old was 0.31. It was significantly smaller than that of primary forests (0.58). In a primary dipterocarp forest plot, light-wood species grew faster in diameter than heavy-wood species. Water content ranged from 0.26 to 0.76. Heavy wood had low water content. Among light-wood species, some (Shorea, Artocarpus) had low water contents and others (Ficus) had high water contents. Some riverine trees also had high water contents. These wood properties appear strongly related to the life history of trees and successional stage.     

Age versus size determination of radial variation in wood specific gravity: lessons from eccentrics

Radial increases in wood specific gravity have been shown to characterize early successional trees from tropical forests. Here, we develop and apply a novel method to test whether radial increases are determined by tree age or tree size. The method compares the slopes of specific gravity changes across a short radius and a long radius of trees with eccentric trunks. If radial changes are determined by size, then the slope of the change should be the same on both radii. If radial changes are determined by age, then the slope should be greater on the short radius. For 30 trees from 12 species with eccentricity of at least 4%, the ratio of the slopes of the linear regressions of specific gravity on radial distance (short radius slope/long radius slope) was regressed on the ratio of radii lengths (long radius/short radius). The regression was highly significant, and the faster increase in specific gravity on the short radius was sufficient to compensate for the difference in radius lengths, so the specific gravity of wood along the short radius was equal to the specific gravity on the long radius at any given proportional distance on the radius. Therefore, trees that are producing xylem faster on one radius than another produce wood of comparable specific gravity on both radii at the same time, so radial increases in specific gravity are dependent on tree age, not tree size.     

Measuring wood preference in termites

Feeding preferences of xylophagous termites have been determined by comparing differences in wood biomass removed, percentage of wood consumed or degree of damage rated in arbitrary categories. When test woods differ in physical characteristics such as density, these measures are not comparable. We examined the response of the Formosan termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) to wood that differed in physical characteristics by compressing blocks to 40% greater than the natural density. Termites ate significantly greater percentages, but similar amounts of biomass, of uncompressed over compressed natural pine. In contrast, they ate significantly greater amounts of biomass, but similar percentages, of compressed over uncompressed mahogany. Whether percentage or amount of biomass removed should be used as a measure of preference depends on what regulates insect meal size. If termites consume meals of fixed biomass, then biomass consumed is the correct measure; percentage removed is appropriate if they consume meals of fixed volume.Deceased, July 25, 1989     

The relationship between stem and branch wood specific gravity and the ability of each measure to predict leaf area

A few trait axes that represent differential biomass allocation may summarize plant life-history strategies. Here we examine one of these axes described by wood specific gravity. Wood specific gravity represents the location of a species on a continuum of the rate of growth vs. the likelihood of mechanical failure, ranging from rapid volumetric growth/increased probability of mechanical failure to slow volumetric growth/decreased probability of mechanical failure. Wood specific gravity has been quantified primarily using three separate methods: a section from terminal branch, a section from the main stem or from a trunk wood core. What is unclear is how comparable these methods are and whether one or the other is a better predictor of other important plant traits such as leaf area. Here we measured stem and branch wood specific gravities from individual trees and shrubs in a tropical rain forest, quantified their relationship and determined their ability to predict leaf area. Stem and branch measures were highly correlated with each measure having a weak correlation with leaf area in trees and strong correlation with leaf area in shrubs. These results indicate that various methodologies for measuring wood specific gravity are comparable, and thus less destructive methods than are currently used are available to determine values for this important trait.     

Measuring and modelling stem growth and wood formation: An overview

The immediate environment of a cambial initial (weather and nutritional factors, growth regulators, physical stresses) varies continuously over time. Consequently local conditions in the cambium influencing wood formation at any given instant are unique. The distribution of these conditions can be influenced by longitudinal gradients (stem base to apex), circumferentially or by local factors, such as proximity to branches. Not surprisingly, therefore, the variation in wood properties within a stem is large and in seasonal climates, the greatest variation is typically found within an annual ring.A great advantage for the study of wood is that the net product of seasonal processes is recorded in the wood structure across the stem radius. Thus by studying the pattern of wood property variation, within the context of its growth history, we can gain insight into cause and effect relationships between the drivers of wood variability. Combining this with temporal, high-resolution measurements of stem growth, weather, and process modelling enables us to better understand and test hypotheses of wood formation and the causes of variability in wood properties.Over recent years and in partnership with industry and other research providers, we have been attempting to model tree growth (Cabala) and cambial activity (TreeRing and CAMBIUM) at a daily time step to explain radial variability in wood properties. CAMBIUM is the latest development of this effort, modelling a population of eucalypt cambial cells, accounting for fibre and vessel formation using physiologically meaningful relationships.     

Wood specific gravity and anatomy in Heliocarpus appendiculatus (Tiliaceae)

Specific gravity exhibits extremely large radial increases with distance from the pith in Heliocarpus appendiculatus Turcz. (Tiliaceae), a pioneer of neotropical wet forests. To determine some of the wood anatomical changes associated with this increase, wood samples taken at breast height from three trees were divided into 1.0-cm-long segments from pith to bark. Measurements were made of fiber wall thickness, fiber lumen diameter, and percentages of fibers, axial parenchyma, ray parenchyma, and vessels on sections prepared from each segment. The extreme radial increases in specific gravity were associated with increases in fiber wall thickness, decreases in fiber diameter, decreases in fiber lumen diameter, and changes in the relative proportions of fibers and parenchyma. The increase in percent fiber concomitant with a decrease in axial parenchyma was the most important contributor to the increase in specific gravity in this species. The best predictor of specific gravity was percent fibers (r = 0.91, 0.92, 0.94) or percent axial parenchyma (r = -0.92, -0.91, -0.95), two variables that were highly intercorrelated (r = -0.95, -0.98, -0.99).     

Measuring cell-type specific differential methylation in human brain tissue

The behavior of epigenetic mechanisms in the brain is obscured by tissue heterogeneity and disease-related histological changes. Not accounting for these confounders leads to biased results. We develop a statistical methodology that estimates and adjusts for celltype composition by decomposing neuronal and non-neuronal differential signal. This method provides a conceptual framework for deconvolving heterogeneous epigenetic data from postmortem brain studies. We apply it to find cell-specific differentially methylated regions between prefrontal cortex and hippocampus. We demonstrate the utility of the method on both Infinium 450k and CHARM data.