Andrew D. Cameron

Crown, stem and wood properties of wind-damaged and undamaged Sitka spruce

Abstract The study investigated the differences in slenderness ratio of all the snapped, overturned or undamaged trees within a wind-damaged stand of Sitka spruce containing areas of both, wet and dry soils. In addition, crown size, proportion of compression wood and mechanical properties of wood were investigated on 12 sets of trees of similar diameter that had snapped, overturned or remained undamaged from each of two further wind-damaged stands of Sitka spruce. No difference in stem diameter, height or slenderness ratio were found between the damaged and undamaged trees sampled from the dry part of the wind-damaged stand. On the wet part of the site, however, the snapped trees were found to be significantly taller and of greater diameter than the undamaged or overturned trees although slenderness ratios were similar for all trees. The experiment investigating matched sets of trees found that the snapped and overturned trees had significantly smaller crowns than the undamaged trees. Furthermore, the snapped trees had wood in the outer part of the stem that was less stiff, but of bending strength similar to that of similar wood taken from the undamaged and overturned trees. According to the results, high proportions of compression wood may be involved in the occurrence of storm damage. It is suggested that trees containing compression wood should be preferentially removed from the forest during thinning. Since it is not feasible to measure compression wood in standing trees, the presence of leaning stems or asymmetric crowns should be used to identify the trees to be removed. Furthermore, trees with small crowns should also be preferentially removed during thinning.

Influence of overstorey basal area on density and growth of advance regeneration of Sitka spruce in variably thinned stands

The aim of this study was to investigate the effect of the overstorey, as characterised by basal area, on seedling density and growth of advanced regeneration in two irregularly thinned stands of Sitka spruce (Picea sitchensis (Bong.) Carr.) and to investigate whether any relationships found were affected by the method in which basal area was determined. Surveys were carried out in two contrasting Sitka spruce plantations in which the age and height growth (total and current years) of advance regeneration was measured and basal area of the crop trees was determined using different methods, including point sampling with a range of basal area factors. The density of young (up to 4-year-old) regeneration was found to be positively correlated with overstorey basal area, with the strongest significant relationship, albeit weak (r 2 = 0.18, P < 0.01) found when basal area was determined using point sampling with a basal area factor of 7.5 (metric). Growth of natural regeneration, as determined by total height, leader length and leader/lateral ratio, was found to be negatively correlated with overstorey basal area. The strength of these relationships varied according to how basal area was determined and the significance of this is discussed. In the stand with older regeneration the basal area of the overstorey above those plots where natural regeneration was in check was significantly (P < 0.001) higher than where natural regeneration was growing well. It would appear that in order to encourage growth of the advance regeneration, the stand should be kept at a basal area of 30 m 2 ha -1 or less. This is less than the value (38 m 2 ha -1 ) for a fully stocked stand [Edwards, P.N., Christie, J.M., 1981. Yield models for forest management. Forestry Commission Booklet 48, HMSO].

Effect of nursing mixtures on stem form, crown size, branching habit and wood properties of Sitka spruce (Picea sitchensis (Bong.) Carr.)

This study investigated the effects of Alaskan lodgepole pine (Pinus contorta Loud.) and hybrid larch (Larix x eurolepis Henry) nurses, planted in triplet mixture with Sitka spruce (Picea sitchensis (Bong.) Carr.), on growth rate, stem form, branching habit and wood properties of the spruce. These mixtures were compared with pure stands of Sitka spruce which had been regularly and periodically fertilised with nitrogen. Hybrid larch promoted diameter increments in Sitka spruce greater than those achieved by the other treatments over the last 12 years of the experiment (current age 30 years). Growth of regularly fertilised pure Sitka spruce was not significantly greater than that of periodically fertilised pure spruce, suggesting that regular applications of nitrogen fertiliser did not result in increased stem growth. The greatest increase in growth of the larch-nursed spruce occurred during the period immediately following canopy closure, thus demonstrating the failure of the larch to compete with the spruce crowns. This period of high growth was associated with a high branch, cross-sectional area and deep knots within the wood on the lower part of the spruce stems in comparison with other treatments. While each treatment was associated with a similar number of branches, lodgepole pine-nursed spruce had more small branches (0-10 mm diameter) and fewer big branches (>20 mm diameter) compared with other treatments, highlighting the capacity of lodgepole pine to control branch development of the spruce. Spruce trees nursed by larch had deeper and more imbalanced living crowns with longer lived branches in comparison with lodgepole pine-nursed spruce, and both the pure spruce treatments, suggesting that more juvenile wood may have fonned within the stem. Larch-nursed spruce also had the highest stem taper and lodgepole pine-nursed spruce the lowest. Basic wood density was not influenced by treatments. Overall, the evidence from this study suggests that the use of larch as a nursing species on deep peats is inadvisable and that Alaskan lodgepole pine is better able to control the branching habit of Sitka spruce with the prospect of better quality sawlogs in the future, albeit with a lower average tree size. Periodically fertilised pure spruce appears to maintain a growth rate consistently above that of the lodgepole pine-nursed spruce but without many of the disadvantages linked with the regularly fertilised pure spruce, particularly the development of large branches and an irregular pattern of annual rings within the wood.

Effect of thinning on the development of compression wood in stems of Corsican pine

This study considered the effects of thinning on the development of compression wood in stems of 35-year-old stand of Corsican pine (Pinus nigra L.). Part of the stand had been thinned at 5-yearly intervals and part left unthinned. Twenty trees each from the thinned and unthinned stands were randomly selected and felled. Measurements were made on tree height, stem diameter, stem slenderness and canopy depth. Wood samples were removed from the central part of the main log and cross-sectional measurements made on ring width, basic density and compression wood content. Cross-sectional area of compression wood was found to be three time higher in stems from the unthinned trees in comparison with those from the thinned trees. No significant differences in mean radial ring width or basic density were found between treatments. Correlations indicated that, with increasing in stem diameter, compression wood content increased in the unthinned trees, while a decline in compression was observed in the thinned trees. Tree height was also positively correlated with compression wood content in unthinned trees, while no equivalent relationship was observed in thinned trees. Observations from this study, while not conclusive, suggest that phototropic stimulus may be producing stem inclinations in the unthinned stand as trees compete for space in the canopy, whereas crown competition has been largely eliminated in the thinned stand; and that this is responsible for compression wood levels recorded in this study.

The potential to improve growth rate and quality traits of stem straightness and branching habit when breeding Picea sitchensis (Bong.) Carr

BackgroundTree breeders continue to use visual assessments of stem shape and branching habit as part of their selection criteria because these are key features used by timber merchants in assessing stand value. However, it is not known how effective these assessments are in introducing real improvements in stem and branching traits to breeding and production populations of Sitka spruce. This study determined the genetic characteristics of several traits associated with stem straightness and branching, and examined whether these traits are suitable as future selection criteria.MethodsTrees were sampled from 33 families selected from a 20-year-old half-sibling progeny trial growing in northern Scotland and a control of directly imported material from Queen Charlotte Islands, Canada. Stem straightness and branching habit were ‘scored’ for quality in addition to direct measurements made on growth and branching characteristics.ResultsResults indicate that heritability values for most external stem and branching properties evaluated visually are sufficiently strong to enable effective selection in tree improvement programmes. Estimated genetic correlations suggest that substantial improvements in branch and stem quality could be achieved without a reduction in growth rate.ConclusionsVisual scoring systems appear to successfully target families of good growth and small branch size relative to the control population.

Determining the sustainable normal irregular condition: A provisional study on a transformed, irregular mixed species stand in Scotland

Abstract The aim of this study was to determine whether the sustainable irregular condition has been achieved in a rare example of a mixed-species irregular stand located in Faskally Forest, Scotland. The stand has been undergoing transformation over the past 60years and is now managed under the selection system. Comparisons of diameter distribution, stand increment and recruitment through natural regeneration were made in a 1ha permanent sample plot following two harvesting interventions separated by an interval of 6years. Results indicate that while the age-class distribution was approximately bimodal, the stem number/diameter distribution followed a negative exponential curve, a key characteristic of the balanced irregular state. The q-value, representing the diminution of stem numbers from one diameter class to the next, remained relatively stable between the first and second inventories (1.6 and 1.5, respectively) in spite of a reduction in overall stem numbers and basal area. Nevertheless, the stand appears to be in a state of flux, with a clear shift in species composition observed within the regeneration pool between inventories; the shade- and semi-shade-tolerant species being favoured at the expense of the shade-intolerant species. Recruitment through natural regeneration appears to have responded to the reduction in canopy and basal area in the harvesting intervention before the second inventory, although it is not clear whether this is sufficient to maintain the distribution in perpetuity. Alternative stem number/diameter distributions are considered in terms of biological and economic sustainability.

Role of monoterpenes in Hylobius abietis damage levels between cuttings and seedlings of Picea sitchensis

Abstract This study investigated the role of monoterpenes, a group of chemicals known to be involved in plant defence, in the susceptibility of Sitka spruce [Picea sitchensis (Bong.) Carr.] plants derived from both cuttings and seedlings to attack by the large pine weevil Hylobius abietis (L.). Results showed that, given the choice, weevils prefer to feed on the shoots of seedlings than of cuttings and that this preference continued over a period of 6 days, although the overall level of feeding declined. This observation was associated with a higher level of monoterpenes in the shoots from cuttings than in those from seedlings. When the weevils were restricted to the stems and given no choice, levels of damage to the bark were similar in both plant types.

Assessing the compensation for electricity wayleaves

This paper examines the measure of compensation payable for electricity wayleaves through afforestation and considers the merits of using a discounted cash flow approach to calculate the level of compensation. The research finds that the majority of negotiations take place “under the shadow” of compulsory powers and that the measure of compensation is based on the principle of equivalence; the compensation payable being the loss to the landowner and not the gain to the electricity supply company. It concludes that great caution is needed when applying a discounted cash flow approach to the valuation of afforestation owing to the large number of inputs and the sensitivity of the estimated land value to changes to key variables such as the discount rate and tree species.

Variation in the incidence and severity of drought crack in three conifer species in North East Scotland

ABSTRACT The incidence of longitudinal drought cracks in coniferous trees may increase as a consequence of climate change. While larger diameter trees are more prone to splitting, it is unclear why only some of the larger trees within the same stand typically suffer damage. Matched pairs of trees of the same size with and without cracks were studied in two adjacent pole-stage mixed stands of Sitka spruce/grand fir (Picea sitchensis/Abies grandis) and Sitka spruce/noble fir (Picea sitchensis/Abies procera) located in North-East Scotland. A range of attributes were measured on 15 damaged and undamaged trees of each species. Length and position of cracks on stems were also recorded, and annual ring width and latewood percentage measured on cores. Noble fir had significantly longer cracks and these were located higher in the stem than the other species. Fewer cracks formed on east-facing side of stems in all species suggesting that prevailing westerly winds may place greater tensile forces on the damaged sides of stems. A higher proportion of latewood (associated with higher tangential shrinkage) was found in the firs and may explain the greater incidence of cracking on grand and noble fir stems (13% and 16%, respectively) in comparison with Sitka spruce (3%).