Variation of ring width and specific gravity within trees from unthinned Sitka spruce spacing trial in Clocaenog, North Wales

The aim of this work was to quantify patterns of change in ringwidth and specific gravity within trees of Picea sitchensiswith ring number across juvenile and mature wood, in relationto height in tree, original spacing, and crown dimensions. Fivetrees were sampled from each of three plots on a 52-year-oldunthinned spacing trial at Clocaenog, North Wales. The ring width of wood produced in early decades of the plantationwas most strongly correlated with original spacing, while thatproduced in later decades was more strongly correlated withbranch diameters of the upper crown. In later decades, treesoriginally at the widest spacing had higher specific gravitythan those originally at closer spacing, presumably associatedwith self-thinning of the narrower-spaced unthinned plots. Differencesin amount of juvenile wood between spacing plots were less markedthan those reported from the same plots when harvested 7 yearsearlier; it is suggested that as trees surviving after self-thinningare likely to be those with a competitive advantage from anearly stage, differences between plots in amounts of juvenilewood may become less apparent in trees harvested later in therotation than in those sampled earlier. Underlying patterns of variation in ring width and specificgravity across the tree were found to be modified by a progressivedrift with height in the tree. Linear regressions between specificgravity and ring width also varied in a systematic way; theintercept and slope of these regressions tended to increasewith ring number from the pith, and with height in tree at aspecified ring number. Equations are given as a basis for quantifyingthese trends, but more data are needed from other sites to determinethe extent to which these equations represent trends inherentto cambial and apical ageing, as distinct from influence ofchanging environment around the trees.     

A Phytotoxic Effect of Captan on the Growth of Conifer Seedlings

Captan was found to have an inhibitory effect on the seedlinggrowth of Picea sitchensis, Pinus sylvestris, and Tsuga heterophylla.A single application of captan reduced the rate of shoot growthfor at least two weeks, with a further decrease after a secondtreatment. Seedlings grown in sand appeared to be more adverselyaffected than those grown in soil. Weights of root, shoot, andleaves were all reduced in treated plants grown in sand. Nophytotoxic effects were detected when captan was applied totomato, barley, or cress seedlings grown in either sand or soil. It is suggested that the use of captan should be avoided duringgrowth analysis experiments on conifer seedlings, or, if fungalproblems make its use desirable, experimentation should be delayedfor at least three weeks after treatment.     

Tracheid Dimensions in Relation to Shoot Vigour in Picea

Radial tracheid diameter is shown to be correlated with rateof shoot growth in Picea sitchensis and Picea abies; this relationshippresumably accounts for the negative correlation between rateof shoot growth and calculated wall material per unit area,since wall thickness does not vary with shoot vigour. Tracheiddiameter is also correlated with ring width and rate of xylemincrement in P. abies. It is suggested that it may be possibleto predict wood density from the rate of shoot elongation, asdistinct from its duration.     

Variation in density of Picea sitchensis in relation to within-tree trends in tracheid diameter and wall thickness

The influences of cambial age and ring width on density of Sitkaspruce (Picea sitchensis (Bong.) Carr) were analysed in relationto within-tree trends in tracheid diameter and cell wall thickness.Discs were sampled at breast height from a total of 24 trees,from seven stands at three contrasting sites in Wales, and atbreast height, 30 per cent and 60 per cent total tree heightfrom one of the stands. Across the juvenile wood, ring density decreased with ring numberfrom the pith while radial tracheid diameter increased. Theseoverall trends were considered to be inherent to tree growth,presumably associated with cambial ageing, since they occurredin all trees on all sites. In juvenile wood, density also variedwith site growth rate (as indicated by ring width) at similarcambial age, wider rings being associated with more rapidrateof change in tracheid diameter with ring number and with decreasein tracheid wall thickness. Consequently, on a site having treeswith high growth rate density decreased more rapidly acrossthe juvenile wood, down to a lower minimum value, than on siteswith a slower growth rate. In mature wood, the decrease in densitywith increase in ring width was associated with differencesin both tracheid diameter and wall thickness. Density was slightly(though not significantly) higher at breast height than in comparablerings at 30 per cent total height, associated with significantlythicker tracheid walls at breast height. Changes in radial tracheid diameter (with ring number, or withring width) were associated with greater differences in theearlywood than towards the latewood end of each growth ring,while variations in wall thickness with ring width were associatedwith rate of increase in wall thickness towards the latewoodend. This may account for some previously conflicting reportson influence of silvicultural management on density, for densityis likely to vary with influence of environment on the seasonalcycle of cambial activity. The extent of the juvenile wood as delimited by the inner coreof wide growth rings does not necessarily correspond to theregion of varying tracheid dimensions in Sitka spruce.