Natural durability of Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) heartwood grown in southern Germany

Abstract

The natural durability of timber is an important property in order to assess its performance in service. For numerous species grown in primary forests, this property has already been determined. As plantation-grown timber becomes more and more important, detailed information on its properties is needed, because increasing amounts of this material are coming to the market. The majority of planted Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) in Germany is around 40 years old. In the present study, representative material of totally ten trees from two different sites in the south of Germany was investigated with regard to natural durability. In laboratory tests based on European standard DIN EN 350-1, inner and outer heartwood zones were exposed to basidiomycetes. Density measurements were additionally used for further characterisation of this material. Results showed a lower durability of the plantation-grown Douglas fir wood as compared with wood from natural sites. Significant differences for both durability and density were found between inner and outer heartwood, even though no correlation between the parameters was recognised. Data illustrate that for a better understanding of durability variations, chemical, topochemical and electron microscopic studies are needed.     

Stamm- und Wurzelfäulen in Douglasien,Pseudotsuga menziesii (Mirb.) Franco1

Stem and root rot of Douglas fir, Pseudotsuga menziesii (Mirb.) Franco. In 20 year old Douglas fir most of the butt rot was caused by Fomes annosus. Stem decay was central as well as eccentric reaching the sap wood in either case. The side roots of 20 year old Douglas fir were compared with those of a 40 year old stand with butt rot. In individual trees with decay there were less roots with Fomes annosus decay in the younger stand. Calocera viscosa was more abundant in the older stand. Soil conditions which might have favoured root rot in the young stand are discussed.     

Response of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) to some different fertilizers applied at planting

Four fertilization at planting experiments were conducted with Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) on eastern Vancouver Island. In experiment 1 Agriform (20-10-5, AGR) and Osmocote (17-7-12, OSM) supplied N at 0, 4.2, 8.4, 16.8 or 33.6 g/tree either broadcast, within 15 cm of the tree, or in a hole 15 cm from the tree (adjacent). In experiment 2 AGR, diammonium phosphate (21-55-0, DAP), ammonium sulphate (21-0-0, AMS), sulphur coated urea (35-0-0, SCU) supplied N at 0, 8.4, 16.8 and 25.2 g/tree. Triple superphosphate (0-45-0, TSP) supplied P at the same levels as DAP: 0, 9.6, 19.2 and 28.8 g/tree. In experiment 3 AGR and SCU (32-0-0) supplied N at 0, 8.4 and 16.8 g/tree. In experiment 4 DAP was used to fertilize trees on five different dates, between March and October, and each treatment supplied 16 g N/tree. Two-year old, bare root, planting stock was used except in experiment 3, where container stock was compared with bare root stock.Little growth response was obtained after one year, but height growth responses of 12 to 31% were measured after 3 to 6 years with fertilizers supply 8.4 to 16.8 g N per tree. Growth responses were little affected by the type of fertilizer and were primarily due to N, with release rate having no marked effect. The exception to this was TSP which did not increase growth but did increase survival. Survival was reduced by AMS and to a lesser extent by AGR. Container seedlings responded more to fertilization at planting than bare root seedlings.Seedling N, P and K concentrations and contents declined following planting for 6 months and only started to recover after July. Application of fertilizer caused a small increase in seedling nutrient concentration regardless of date, but this had no detectable effect on dry weight measured six weeks later.     

Influence of initial plant density on sawn timber properties for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

? Context

Mechanical wood properties are increasingly relevant for structural applications and are influenced by growing space availability. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) has an increasing market share in Europe and is mainly processed to sawn timber.

? Aim

A sample of 164 thinning trees was taken from two Douglas-fir long-term forestry research plots in Germany. The end-use quality of about 2,000 side and center boards was analyzed as a function of initial plant density (1,000, 2,000, and 4,000 trees per hectare) and log position within the stem.

? Methods

Sawn timber quality was described by knottiness, density, modulus of elasticity, and strength. Explanatory parameters were radial position, longitudinal position, and initial plant density. All boards were strength graded visually and by the grading machine GoldenEye-706 using both X-rays for detecting densities and size as well as position of knots and laser interferometry for detecting eigenfrequency (DIN 4074, DIN 2012; EN 14081-2, CEN 2010).

? Results

High plant density led to better mechanical sawn timber quality. Significant differences were especially observed between 1,000 and 2,000 trees per hectare. The yield of machine strength-graded center boards of strength class C24 increased from 50 to 89 % at low and high initial plant density, respectively.

? Conclusion

Foresters are able to improve end-product quality by controlling planting density in particular. The roundwood price that foresters get should be based on the proportion of higher strength classes within logs to give incentives for a more quality-oriented forest management.     

Growth reaction patterns of tree height,diameter, and volume of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) under acute drought stress in Southern Germany

Climate change in Central Europe may come along with acute drought stress, which can severely reduce growth and vitality of forest trees and whole stands. For a tree species such as Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) which is cultivated far beyond its natural range in Europe, knowledge of its behaviour under stress is crucial for the cultivation of Douglas-fir in view of a changing climate. Because of its easy accessibility, growth response to stress was mainly studied based on diameter growth at breast height. In long-term experiments on one dry and one moist site in Southern Germany, stem analyses of 133 mature and even-aged Douglas-firs were performed. The short-term growth reaction pattern under acute drought stress of 2003 had not only consequences on diameter but more pronounced effects can be observed when studying tree height: Respecting the different age trends by previous detrending, height increment only reacted more sensitive on the dry site. We also showed that extrapolating a particular decline in basal area increment to the whole stem can result in misunderstandings. However, results were less biased, when original data were smoothed or short-term assessment of volume growth was based on basal area measurements. By means of a linear mixed model approach, the influence of site, tree, and stand characteristics on Lloret’s indices of resistance and resilience (Lloret et al. in Oikos 120:1909–1920. doi:10.1111/j.1600-0706.2011.19372.x, 2011) were analysed. For Douglas-fir, site played a crucial role and became more important considering the age trend. On the contrary, the positive influence of site quality on drought tolerance decreased with data processing. However, more growing space by thinning can advance tree resistance and resilience regarding height, diameter, and volume growth. Large individual crown volume improved the growth pattern under drought, and large stand density impaired it. Douglas-fir is obviously equipped with a morphological variability, which fosters lateral rather than vertical growth allocation under severe stress. Silviculture can mitigate stress through the choice of the site and through lower stand densities by thinning. Our refined stress response analysis confirmed a favourable growth and resilience of Douglas-fir even under extreme drought events.     

Effects of the clear-cutting of a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation on chemical soil fertility

? Stand harvesting and regeneration were usually considered to be a critical phase for the sustainability of forest soils. The present study concerned the effects on soil chemical fertility of the clear-cutting of a highly productive Douglas-fir stand aged 67 years that was clear-cut with no disturbance.

? Results showed that soil changes were rapid in the three-year period following the cutting. The forest floor mass considerably decreased and the mineral soil showed a limited but real acidification. Soil losses represented 4% of the available nutrients over a depth of 60 cm for N, 22% for K, 25% for Ca and 32% for Mg. Only P increased by 11%. Due to the spatial variability of forest soils, and despite regular re-sampling, confidence intervals were large and difficult to reduce.

? The reversibility of the effects of the clear-cutting and its consequences on soil functions depend on the element: it should not be a problem for C, N and K, which would recover when the biological cycle is re-established once again in the young stand. Phosphorus is not at issue since it changes form in the soil. The depletion of Ca, and to a lesser extent of Mg, is of some concern as a result of limited soil reserves, the limited flux of cations from the mineral changes in the soil, the relatively large part of Ca and Mg in the forest floor, and the negative input-output budgets for those elements.

? The duration of the impact of the clear-cutting on soil requires medium-term observations because it cannot be deduced from the current knowledge of this ecosystem.

     

Fomes annosus (Fr.) Cke. und andere Stammfäulepilze in einem Douglasienbestand,Pseudotsuga menziesii (Mirb.) Franco1

Fomes annosus (Fr.) Cke. and other decay fungi in a Douglas fir stand, Pseudotsuga menziesii (Mirb.) Franco. 40% of the trees in a 40 years old Pseudotsuga menziesii stand showed butt rot. 85 trees were analysed for decay fungi. Fomes annosus, the most frequent fungus, also invaded the sap wood. Factors of the soil favourable to the rot and the possibility of transmission of the most frequent decay fungus, Fomes annosus, from (a) neighbouring spruce stands, (b) from the roots of Scots pine from the previous crop arc discussed. Caniophora puteana was isolated from about 10% of the butt rots. The importance of Calocera viscosa which grew out of the central decay of twelve trees as a decay fungus is still under investigation.     

Fertilisation with biosolids in a silvopastoral system established with Pseudotsuga menziesii (Mirb.) Franco in Galicia (NW Spain)

Agroforestry Systems - In Europe, sewage sludge has to be stabilised before its use as fertiliser in agricultural land. Stabilisation processes can cause differences in the concentration of heavy...     

Genetic control of the tree-ring response of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) to the 2003 drought and heat-wave in France

The genetic control of tree ring growth in Douglas-fir in response to the drought and heat-wave that occurred in 2003 in Europe was studied with microdensity profiles in three clonal experiments located in three different French regions. The drought and heat-wave significantly affected Douglas-fir wood formation. The Chassenoix site (Northeast of Massif-Central) was more severely affected that the other two: the 2003 year-ring was narrower and less dense than in the other sites and than the previous (2002) and following (2004) year-rings in the same site: ring growth stopped earlier and latewood did not develop completely. The year-rings 2004 and 2002 were very similar in this site. There was a significant genetic control for all ring parameters in the three sites and during the three years. The heritability was highly variable between years and among sites, without any clear pattern in this variability, except in Chassenoix where it was slightly lower in the 2003 year-ring. Variables measuring the response of trees to the 2003 event, i.e., the difference in ring width between 2002 and 2003, or between 2003 and 2004, showed a very variable degree of genetic control, from very low to relatively high. Douglas-fir seemed plastic enough to acclimate to the drought and heat-wave and then to recover during 2004. Furthermore the level of heritability estimated demonstrates that Douglas-fir has an adaptive potential that could be useful for multi-generation long-term response.     

Root growth and water use efficiency of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings

One-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings were grown for 17 weeks in 100-cm deep, 7.8-liter containers. Two Douglas-fir provenances, one from a wet and one from a dry site in coastal British Columbia, and two lodgepole pine provenances, one from a wet and one from a dry site in interior British Columbia, were grown in wet (522% water content) or dry (318% water content) peat/vermiculite soil in a factorial design. Each container was sealed so that water loss occurred only through the seedling. Five harvests were made at three to five week intervals and water use, dry matter increment, root length and root weight were determined at each harvest. Stomatal conductance and shoot water potentials were measured during the last 12 weeks of the experiment. Lodgepole pine seedlings had greater dry matter production, water use, stomatal conductance and new root length than Douglas-fir seedlings. New root weight of lodgepole pine seedlings exceeded that of Douglas-fir seedlings during the last five weeks of the experiment, and specific root length (root length per unit root weight) of new roots was higher for lodgepole pine seedlings throughout the experiment. Douglas-fir seedlings showed higher water use efficiency (WUE) than lodgepole pine seedlings, and both species showed higher WUE in the dry soil treatment. Douglas-fir seedlings had lower water potentials and higher water uptake rates per unit of new root length than lodgepole pine seedlings, although water uptake rates per unit of root dry weight showed little difference between species. Soil water treatment influenced specific root length of new roots, water uptake per unit of new root length, and WUE in Douglas-fir seedlings more than in lodgepole pine seedlings.     

Effect of wide spacing on tree growth, branch and sapwood properties of young Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] in south-western Germany

The influence of stand density on Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is conceptually understood, but for wide spacings not well quantified, particularly in Europe. This study used 41 trees from 7 different locations in south-western Germany to compare important tree- and branch-level attributes across three different densities, namely 100, 200, and 1,200 stems ha⁻¹. In general, there were only a few tree and branch attributes that were significantly different between the 100 and 200 ha⁻¹ densities. Crown projection area and diameter of the thickest branches were the most important differences between the 100 and 200 ha⁻¹ densities. The most obvious and significant differences in this study were between 100 and 1,200 ha⁻¹ densities, where nearly every examined tree and branch attributes were statistically significant. However, relative sapwood area, the number of branches, branch angle, and the occurrence of spike knots were insensitive to stand density. Although the two lowest stand densities in this study represent rather extremely wide spacings, these results still have important implications for the development of effective thinning regimes for Douglas-fir in south-western Germany. Important management recommendations from this study include thinned stands should be maintained to at least 200 stems ha⁻¹ to maintain high log quality and stand stability. Furthermore, even at stand densities exceeding more than 1,200 trees ha⁻¹ planted trees, artificial pruning may even be necessary to produce high quality logs.     

Response of planted beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) saplings to herbaceous and small shrubs control on clearcuts

The reaction of young beech (Fagus sylvatica L.) and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) saplings on competition of two types of vegetation—(1) gramineous with mainly Agrostis capillaries, Calamagrostis epigejos, Deschampsia flexuosa, and (2) small shrubs with mainly Rubus fruticosus and R. idaeus—on clear cuts on two sites was studied for 2 years. Half the sample saplings were released from competing vegetation by repeated herbicide applications. This treatment significantly raised the diameter increment in both species at the site with higher competition intensity, and more strongly after the removal of small shrubs than after the removal of grasses. Sapling length increment was not significantly affected. After being released from small shrubs, saplings of both species developed a smaller specific fine root length (cm g⁻¹ fine root biomass) than unreleased saplings during the second year which was characterized by low rainfall. Root nitrogen concentration significantly increased after weed control in both vegetation types. Sapling foliar content of main nutritional elements was negatively related to dry mass and total chemical content of surrounding ground vegetation. Based on these results, a release from ground vegetation could be a useful tool to improve growth of planted beech and Douglas-fir saplings on sites with well-developed small shrubs competition (mainly by Rubus fruticosus and R. idaeus), or under fairly dry conditions.     

Polyporus schweinitzii Fr. und Sparassis crispa (Wulf. in Jacq.) ex Fr. als Fäuleerreger in einem Douglasienbestand (Pseudotsuga menziesii (Mirb.) Franco) mit hohem Stammfäuleanteil1

Polyporus (Phaeolus) schweinitzii and Sparassis crispa as frequent decay fungi in Douglas fir. Of fifty, 55 ears old trees in a Pseudotsuga menziesii stand. 90% showed decay of the heart- wood of the butt. The possibility of transmission of the most frequent decay fungi, P. schwei- nitzii and S. crispa, which also are frequent parasites in the roots and butts of pine, from the roots of the Pinus sylvestris trees of the previous crop into the roots of the Douglas fir is discussed. A first identification of the fungi was made possible by storing the stem discs under moist conditions. The mycelia of P. schweinitzii and S. crispa grew out of the decayed wood and possessed a characteristic form and colour.     

Endophytische Pilze in Nadeln von gesunden und geschädigten Fichten (Picea abies [L.] Karsten)

Endophytic fungi in needles of healthy-looking and diseased Norway spruce (Picea abies [L.] Karsten). Endophytic fungi were isolated from surface-sterilized, 5 to 6 year old needles of healthy-looking and diseased trees. Two fungal species could be isolated frequently: Lophodermium piceae and Tiarosporella parca. At any site neither L. piceae nor T. parca could be isolated more frequently from needles of diseased trees. The possible types of relationship between these two fungi and Norway spruce are discussed.