Leaning Trees Research Articles

Growth rings in rimu from south Westland terrace forest

Summary A study of growth rings in relatively fast-grown rimu trees from terrace forest in south Westland revealed a number with conspicuously dark latewood bands. These have been called marker rings. The regular occurrence of these marker rings in the same sequence in a number of trees indicates that growth rings are formed contemporaneously in all relatively fast growing trees. A good correlation between the occurrence of marker rings and cool autumn temperatures in the years in which they were formed is very strong evidence that the rings are formed annually. Discontinuous false rings were found in some fast-grown trees, but continuous false rings were not discovered. Discontinuous growth rings were found in strongly fluted trees, in leaning trees, and in very slow-growing trees. No evidence of missing rings was found, but it is possible that growth rings could be absent from slow-growing trees.

Influence of Cell Wall Composition on the Moisture Relations of Hardwood Timbers

IT has already been shown that the compressive strength of hardwood timbers in the green condition is dependent on the degree of lignification as revealed by the behaviour of thin sections with micro-reagents. Thus tropical timbers, with their greater degree of lignification, are on the average stronger than temperate zone timbers of similar density, and the normal wood of temperate zone hardwoods is stronger than tension wood from leaning trees of the same species1. The difference in strength between normal and tension wood was found to be less pronounced in air-dry than in green wood1, and this observation suggested that the influence of the degree of lignification is affected by the moisture content of the wood. In order to examine this possibility a scrutiny has been made of data in the records of this Laboratory or published by other institutions2,3,4. The data were taken as a whole, without the exclusion of particular species, and a comparison was made (a) between tropical and temperate zone timbers, and (b) between normal and tension wood, the influence of density being taken into consideration. In so far as differences in cell wall composition account for the differences between the properties of the timbers under comparison, our observations indicate that the proportional increase in strength which usually accompanies the drying of wood is less in strongly lignified than in weakly lignified material, and consequently differences in strength which are due to differing degrees of lignification tend to be reduced as wood dries. This provides a partial explanation of the fact that the relationship between compressive strength and density is much closer in air-dry than in green wood, particularly in the case of temperate zone timbers.