A Comparison of Two Techniques for Wood Fibre Isolation - Evaluation by Tensile Tests on Single Fibres with Different Microfibril Angle

Abstract: Fibres (tracheids) of spruce ( Picea abies [L.] Karst.) were isolated by means of two isolation techniques. On the one hand, a soft chemical treatment with Jeffrey solution was used. The isolation was carried out with a reduced time of treatment (2 h), just to achieve the state where the fibres could be separated easily with tweezers. On the other hand, fibres were directly peeled out with tweezers, taking advantage of the low shear strength between them. Following this approach, a chemical treatment could be avoided completely. In order to compare the isolation techniques, single tracheids from tissue types with different microfibril angle (earlywood, latewood, juvenile wood, opposite wood, compression wood) were tested in the dry state. The microfibril angles were determined by X-ray diffraction. Single tracheids handled with both isolation techniques were strained in microtensile tests and load-strain diagrams were obtained. The chemically treated fibres were found to have much lower strength and stiffness compared to the mechanically isolated fibres, even though the influence of microfibril angle was still obvious for both kinds of treatment. The results clearly show the importance of single fibre extraction to preserve as much as possible the original properties.     

Altitudinal changes in humus form dynamics in a spruce forest at the montane level

An altitudinal transect was studied at the montane level in a spruce forest, in order to describe changes in humus form dynamics. Whatever the elevation, the periodicity of humus form changes is copied on forest dynamics. Spruce regeneration is restricted both in space and time to favourable micro-site conditions accompanying tree fall gaps. One of these conditions is a shift from moder to mull humus form. As a result, this forest ecosystem shows a space-time mosaic pattern. The recovery of mull humus form takes more time as elevation increases and thus the ratio mull:moder progressively decreases. Simultaneously, burrowing earthworms become scarce. Nevertheless mull humus form does not change basically at increased elevation. On the other hand, moder has little organic matter at the lower montane level. At the mid montane level, accumulation of holorganic faeces into OH horizon is maximum. A mor-moder (few faunal traces) is observed during tree growth phase at the upper montane level. Lack of nutrient availability was hypothesized to explain the observed shift from mull to moder or mor-moder during the phase of intense tree growth. An increased independancy between the building of a moder humus profile and the actual accumulation of organic matter was the main change occurring with elevation. The transition to the subalpine level may thus be defined as the highest elevation up to which the forest ecosystem is able to reverse the mor-building process produced by tree growth. The discoupling between primary producers, plant debris accumulation and decomposers observed in the subalpine spruce forest leads to a breaking point in the carrying capability of humus for spruce seedlings. At high elevation spruce seedlings are mainly observed on rotten wood.The influence of humus form dynamics upon forest sustainability was discussed. The lack of humus biological activity at higher elevation was found to be a reason for the weakness of the forest ecosystem faced to the bilberry heath. Forest sustainability depends both on mull and moder. It was observed that moder failed to recover after mull along the forest cycle and turned to mor in harsh climate conditions. Consequences of management practices on the issue of competition between forest and heath were also discussed.     

Needle analyses and graphic vector analyses of Norway spruce and Scots pine stands

 The aims of this study were to test the nutritional condition of young stands of Norway spruce and Scots pine in southernmost Norway, where atmospheric inputs of anthropogenic nitrogen and strong acids, as well as deposition of magnesium by sea spray, are relatively high. There has been general concern about forest health in this region, specifically about nutrient deficiencies and nitrogen saturation caused by the atmospheric pollution. To expand our knowledge about these subjects, needle analyses and graphic vector analyses, as well as tree vigour index and height growth response to fertiliser application, were used as diagnostic tools. The overall conclusion is that phosphorous limitation is probably more frequent than expected in the coastal zone of southern Norway, especially in spruce on shallow soils. It is hypothesised that phosphorous limitation might be a more general problem or will arise as one in a 30 – 60 km coastal zone stretching from southernmost Sweden along the coast to the north and then westwards along the south coast of Norway. Nitrogen saturation in southernmost Norway might already occur on some sites with shallow soils. Needle analyses and graphic vector analyses can yield erroneous results if stress factors other than nutrient supply, e. g. severe drought, determine the growth rate of trees. In addition, the graphic vector analyses require that nutrients applied to the test plots are available to roots early in the growing season, and that needle nutrient concentrations in late autumn reflect those when the needles were formed. Received: 30 May 1995/Accepted: 27 December 1995     

Tree killing by Ips typographus (Coleoptera: Scolytidae) at stand edges with and without colonized felled spruce trees

Abstract 1 To maintain biodiversity in managed spruce forests in Sweden more wind‐felled trees must be retained. However, there is concern among forest owners that this may result in higher tree mortality caused by the spruce bark beetle, Ips typographus (L.) (Col. Scolytidae). 2 To simulate wind‐felled trees, living spruce trees were cut at spruce stand edges bordering fresh clear‐cuttings. Treatments comprised edges with zero, one or five cut trees colonized by I. typographus. Edges with naturally wind‐felled trees colonized by I. typographus were also included in the analyses. 3 During the two following summers, the number of trees killed by I. typographus did not differ between edges with and without felled trees, or between edges with one or five felled trees. 4 Within edges with felled trees, there were more killed trees close to the felled trees than at other parts of the edges. Thus, felled trees provided focal points for attacks within edges. 5 It is concluded that small numbers of wind‐felled trees colonized by I. typographus may be left near spruce stand edges without increasing the risk of beetle‐induced tree mortality.     

Conifer phenolic resistance markers are bark beetle antifeedant semiochemicals

1 Phenols are important in conifer resistance to fungi associated with bark beetles and as markers for resistance to beetle mass‐attacks. However, the mechanism of phenolic activity in conifer resistance to Ips typographus bark beetle remains unclear. 2 By a new bioassay, we tested the effect on host acceptance and tunnelling of male and female I. typographus in an artificial gallery (13 mm long) for 4 h (no‐choice test). To the artificial diet, an aliquot of host (catechin, taxifolin, or resveratrol) or nonhost (E‐conophthorin) compounds was added, singly tested at doses close to those of tree bark. Host acceptance and tunnelling was measured by the amount of diet removed by the insects. 3 All tested chemicals decreased the tunnelling activity of I. typographus, with an antifeedant effect stronger in males and increasing with dose. No mortality was recorded. The nonhost volatile spiroketal, E‐conophthorin, had the highest antifeedant activity both in males and females. Among host compounds, effects and dose–response were weak in females. Both catechin and E‐conophthorin gave a 50% reduction of tunnelling at a concentration of 0.1% for males, the pioneering (host selecting) sex in Ips. The threshold of activity for host compounds to males was at concentrations of 0.03–0.1%, which corresponds to, or is less than, the concentrations reported from spruce host bark. 4 The results allow us to support the hypothesis of a direct behavioural antifeedant mechanism for resistance from those phenols that are particularly active for the pioneering males during tree attack.     

Occurrence and effects of Nosema fumiferanae infections on adult spruce budworm caught above and within the forest canopy

1 Nosema fumiferanae infections in populations of both sexes of spruce budworm Choristoneura fumiferana moths, collected live above the forest canopy (canopy moths), within the tree crown (crown moths) and in drop trays (dead moths), were examined over a 5‐year period in New Brunswick, Canada. 2 The incidence of infection and of moderate–heavy infections in canopy and crown moths of both sexes increased concomitantly with moth eclosion, indicating that N. fumiferanae retards larval/pupal development, with infected moths, particularly those having higher disease loads, emerging later in the season. 3 Infection rates differed among canopy, crown, and dead female, but not male, moths. Canopy (i.e. emigrating) females had a lower incidence of infection, lower incidence of moderate–heavy infections, and had longer forewings and higher dry weights, than crown females. These results suggest that N. fumiferanae infections negatively affect aspects of female, but not male, flight performance. Regardless of infection, forewing length and dry weight of both canopy and crown females declined over the moth flight period, but infected females in both moth types were smaller than their uninfected counterparts. Forewing lengths and dry weights of moderately–heavily infected females were most severely affected. 4 Despite high annual infection rates in parents, only a small percentage of offspring (second‐instar larvae) that established feeding sites each spring were infected, indicating that high rates of horizontal transmission occurred annually throughout the larval period. 5 The present study indicates that whether N. fumiferanae infections are a debilitating sublethal factor in spruce budworm populations depends more on the disease load than on the overall incidence of infection. The potential importance of N. fumiferanae infections on various fitness parameters related to host dispersal is discussed.