The distribution and interrelationship of collapse,volumetric shrinkage,moisture content and density in trees of Eucalyptus regnans F. Muell.

Summary The relationships among collapse, volumetric shrinkage, moisture content and basic density and their distribution within the stem were examined for trees of E. regnans. It was found that collapse and volumetric shrinkage each were significantly related to moisture content (positively), basic density (negatively), and (positively) to the derived values P (per cent of theoretical saturation) and Q (per cent of cell cavity volume containing water). Notwithstanding the inverse association evident between moisture content and density in the living tree, moisture content was shown to be independently related to each of collapse and volumetric shrinkage.Within the stem, collapse and volumetric shrinkage were negatively correlated with height in the tree although the significance of this relationship was qualified by the adjustment for other variables. Samples containing sapwood displayed collapse values significantly lower than heartwood samples. This was reflected in the presence of a positive relationship between collapse and distance from the periphery when all material was considered, but a negative relationship when sapwood-containing samples were omitted. Basic density was positively correlated with height in the tree and negatively correlated with distance from the periphery. Moisture content, P and Q were negatively correlated with both height in the tree and distance from the periphery although the latter relationship for moisture content was dependent on adjustment for density.The highly significant relationship between volumetric shrinkage and collapse suggested that the former could confidently be used in assessing collapse severity. Moisture content was determined to be an independent indirect indicator of collapse whereas basic density, P, Q and green density could all be of indicatory value, especially the last in view of its ease of measurement.     

Collapse,volumetric shrinkage,specific gravity and extractives in Eucalyptus and other species

Summary An examination of shrinkage behaviour in a range of tree species has demonstrated clear differences between eucalypts and other species with respect to the volumetric shrinkage (S)/specific gravity () ratio. The equation S=f proposed by Stamm (1935a, 1952) to relate this ratio to the fibre saturation point (f) was inapplicable in eucalypts, both before reconditioning, where a highly negatively significant linear correlation was observed between S and , and after reconditioning where the correlation was not significant and the regression line indicated S to be nearly constant. Collapse was found to be highly negatively correlated with specific gravity in the eucalypt species and evidently was primarily responsible for the negative S/ relationship before reconditioning.In non-eucalypts S and were highly positively correlated, but the regression line did not pass through the origin and the slope was 10 to 14% less than the value of 28% suggested by Stamm for f. Only when the regression line was artificially forced through zero did the slope approach postulated fibre saturation point values. A power function was proposed as representing a more reasonable fit of the data.In line with these analyses, unit shrinkage (S_u) was shown not to be equivalent to . This lack of equivalence was expressed as S_u divided by basic density () which was termed the R-ratio and which was shown to be equal to the change in volume during shrinkage (or swelling) divided by the associated change in the weight of an equivalent volume of water. R was seldom equal to one, as required by the Stamm formula, and was negatively correlated with specific gravity in both eucalypts and non-eucalypts. A comparison of regression equations showed R values for eucalypts to be significantly different from those of non-eucalypts. Possible uses for the R-ratio were considered.     

Towards defining a wood quality index for the eucalypts: the R-ratio

Summary The derivation of a value termed the R-ratio (the change in external wood volume during shrinkage or swelling per change in the weight of the associated volume of water) and its possible use as an indicator of dimensional stability (Chafe 1986, 1987), has led to its consideration as a potential wood quality index for the eucalypts. An analysis of R with respect to mechanical strength, durability, volumetric shrinkage, collapse and density in 38 species of eucalypts has shown a high degree of correlation and suggests that R could provide a single overall indication of timber quality.While density was more highly correlated with strength and durability than R, the R-ratio was more highly correlated with shrinkage. Also, when predictor criteria (strength, durability, shrinkage, density) were mutually adjusted in multiple regression analysis, R remained significantly correlated with each. When density was similarly regressed against shrinkage, durability and strength, the relationship was not significant for shrinkage.The observed high correlation between durability and density suggests that mass of wood substance is an important criterion in defining resistance to wood decay.The author wishes to thank Dr. W. E. Hillis, Mr. W. G. Keating, Mr. J. Ilic and Mr. E. P. Lhuede for kindly assigning wood quality rankings to the 38 species of Eucalyptus discussed herein     

Tuberculosis in dromedary camels slaughtered in Nigeria: a documentation of lesions at postmortem

Tropical Animal Health and Production - In comparison with other livestock, tuberculosis (TB) in camels has not been extensively studied in Nigeria. Camels in the hands of Nigerian pastoralists...     

Effect of brief presteaming on shrinkage,collapse and other wood-water relationships in Eucalyptus regnans F. Muell

Summary Brief presteaming of green, increment-core segments of mountain ash (E. regnans F. Muell) produced small but significant changes in a number of moisture-shrinkage parameters. Both total volumetric shrinkage and recoverable collapse were significantly greater in presteamed samples, the increase in collapse being largely attributable to an increase in moisture content after reconditioning (M_r). The change in shrinkage after reconditioning also was significantly related to changes in M_r. The change in M_r was interpreted as reflecting altered permeability in presteamed material and was shown to be negatively related to estimated residual collapse. Initial moisture content and per cent saturation showed a highly significant decrease after presteaming, while green volume showed a small but significant increase. Neither the estimated intersection point, unit shrinkage nor the R-ratio were significantly different after presteaming. However, the unit shrinkage-specific gravity relationship was changed by presteaming such that it more closely complied with Stamm's approximation.The author expresses his appreciation to Dr. Alan Miller for assistance with statistical analysis and to Mr. Chris McEvoy for technical assistance     

Radial dislocations in the fibre wall of Eucalyptus regnans trees of high growth stress

Summary Microscopical examination of the xylem of straight Eucalyptus regnans trees of high growth stress revealed the presence of radial dislocations in the secondary wall of many of the fibres. These features were characterized by a localized disruption in the microfibrillar orientation of the cellulose and were evident in both unlignified and lignified cell walls. Dislocations were not detected in trees having low peripheral growth stress. The origin of these features was suggested to lie in the expansion of the cell wall during the relaxation of longitudinal growth stresses following removal of the sample from the tree. A similar origin of the typically convoluted form of the gelatinous layer of tension wood fibres is discussed.The author expresses his appreciation to Dr. J. D. Boyd for helpful discussions.     

Radial variation of collapse,volumetric shrinkage,moisture conent and density in Eucalyptus regnans F. Muell.

Summary Examination of segmented increment cores from three trees of Eucalyptus regnans demonstrated radial variability as follows: collapse increased with distance from the periphery to about 85% of the radius where it commenced a precipitous decline towards the pith; total volumetric shrinkage increased to about 45% of the radius, gradually declined to 85% radius, then abruptly fell as with collapse; moisture content increased to about 75% radius and abruptly declined at 85–90%; basic density declined with distance from the periphery to about 75% radius, then showed a slight increase towards the pith; per cent saturation remained relatively constant from the periphery to about 90% of the radius, then abruptly declined. It is argued that compression failures in the fibre walls of the brittle heart core were responsible for the precipitous decline in collapse, moisture content and per cent saturation near the pith. Examination of data after separation by density into latewood and earlywood increments demonstrated that latewood tends to be more highly water saturated than earlywood. Similar levels of collapse for material of different densities and correspondingly different saturation values indicated that level of saturation was a more important determinant of collapse susceptibility in latewood than in earlywood.     

Collapse,volumetric shrinkage,specific gravity and extractives in Eucalyptus and other species

Summary The influence of extractive content on the shrinkage behaviour in eucalypts was shown by mathematical extraction after making certain assumptions with respect to available data. The slope of the volumetric shrinkage/specific gravity (S/) ratio changed from negative to positive after the theoretical removal of alcohol/benzene/water soluble or NaOH soluble extractives. Statistical analysis of available data suggested that collapse was positively related to the encrusting and extraneous materials and negatively related to the polysaccharide cell wall component. Conversely, normal volumetric shrinkage was positively related to the polysaccharides and negatively related to lignin and extractive content. Mechanisms by which extractive content might influence collapse development were discussed. R-values (change in external volume during shrinkage or swelling per change in weight of equivalent volume of water) appeared to be negatively correlated with extractive content in eucalypts and calculations for other species showed that R progressively increased with cold and hot water extraction. Further analysis suggested that the apparent change in lumen dimensions suggested by particular R-values was mitigated by the bulking effect of extractives in the cell wall. A possible role for R as an indicator of dimensional stability was postulated.     

Shrinkage and collapse in thin sections and blocks of Tasmanian mountain ash regrowth

Summary Shrinkage and moisture content measurements for thin sections of Eucalyptus regnans have shown that although total volumetric shrinkage was positively correlated with specific gravity, the relationship did not conform to the general equation s = f (Stamm 1935, 1952) in that the straight regression line was significantly different from a line passing through the origin. This contrasted with the relationship between shrinkage from 17% EMC to 0% moisture content and specific gravity which, in principle, complied with the Stamm formula. The discrepancy arose because shrinkage from the green condition to 17% EMC was negatively related to specific gravity owing to the high variability of the measured fibre saturation point and its negative correlation with specific gravity. These observations were affirmed in a comparison of unit shrinkage-specific gravity regressions where relationships were positively significant but the regression constants were not.Shrinkage behaviour in blocks of E. regnans did not comply with the Stamm formula although the average fibre saturation point (41.8%) was not significantly different from that for sections (38.2%). The near similarity derived from a significantly greater unit shrinkage in blocks (0.49) than that in sections (0.30). It was suggested that the much greater external shrinkage in blocks contained a significant increment of cell collapse induced by drying stress below the fibre saturation point.The authors wish to thank Dr. Allan Miller for statistical assistance and Dr. Aleck Hunter for mathematical assessment     

Perforation hyphae of soft rot fungi in the wood of white spruce [Picea glauca (Moench.) Voss.]

Summary Observations made on ponded white spruce wood with the electron microscope revealed that initial branching of perforation hyphae of soft rot fungi did not parallel microfibrillar orientation in the S₂ wall layer but rather occurred perpendicular to this alignment. In the absence of structural evidence suggesting mechanical entry it appeared that cell wall pencetration was accomplished through enzymatic activity at the hyphal apex.The authors wish to express their thanks to Miss S. Godkin and Mr. G. Chauret for technical assistance.