Urban Bergsten

Batch measurements of wood density on intact or prepared drill cores using x-ray microdensitometry

Abstract The performance of a batch scanning x-ray densitometer for measuring wood density without sample preparation, i.e., on intact drill cores, or on rectangular samples prepared from drill cores, was analysed. Effects of x-ray intensity, sample thickness and fiber direction, as well as extractives content, were evaluated for young (mainly sapwood) and old (mainly heartwood) wood from Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). The x-ray power level used as standard (1.4 kW; 40 kV and 35 mA) seemed appropriate for the tested species and specimen thickness. The density of intact drill cores could be determined with a mean standard deviation of 1.6% for each sample, with a single machine run, if the cores were mounted with a fixed fiber direction and calibrations were made for each wood type. The corresponding precision for rectangular samples was 1.0%. Further improvements are attainable by using standard reference samples in each machine run and batch-wise analysis. For the chosen wood types and measurement technique, a sample thickness of 5 mm should give the best precision. However, for species with very narrow rings, thinner samples would improve the spatial resolution when ring boundaries are angled or curved. Extractives should be removed, especially for pine, but possibly also for spruce, if high precision in density determination is required.

Prediction of basic wood properties for Norway spruce. Interpretation of Near Infrared Spectroscopy data using partial least squares regression

Abstract This work was undertaken to investigate the feasibility of using near infrared spectroscopy (NIR) and partial least squares regression (PLS) as a tool to characterize the basic wood properties of Norway Spruce (Picea abies (L.) Karst.). The wood samples originated from a trial located in the province of Västerbotten in Sweden. In this trial, the effects of birch shelterwoods (Betula pendula Roth) of different densities on growth and yield in Norway spruce understorey were examined. All Norway spruce trees in each shelterwood treatment were divided into three growth rate classes based on diameter at breast height (1.3 m) over bark. Five discs were cut from each tree (i.e. from the root stem, and at 20%, 40%, 60%, and 80% of the total height). The discs from 40% tree height were used (i.e., where the largest variations in annual ring widths and wood density were found). A total of 27 discs were selected. The discs were used for measuring annual ring widths, wood density, average fiber length and the fiber length distributions. Milled wood samples prepared from the discs were used for recording NIR spectra. PLS regression was used to generate prediction models for the wood properties (Y-matrix) and NIR spectra (X-matrix) as well as between the wood properties (Y-matrix) and the fiber length distributions (X-matrix). One set of models was generated using untreated spectra and fiber length distributions. For a second set of models the structure in the X-matrix, which was orthogonal to the matrix described by the wood properties, was eliminated using a soft target rotation technique called orthogonal signal correction (OSC). The PLS model obtained using “raw” untreated NIR spectra and fiber length distributions had a poor modeling power as evidenced by the cumulative Q2 values. For the PLS models based on untreated NIR spectra the cumulative Q2 values ranged from a minimum of 16% (wood density) to a maximum of 46% (no. of annual rings). Orthogonal signal correction of the X-matrix (NIR spectra or fiber length distributions) gave PLS models with a modeling power corresponding to cumulative Q2 values well in excess of 70%. The improvement in predictive ability accomplished by the OSC procedure was verified by placing four of the 27 observations in an external test set and comparing RMSEP values for the test set observations without OSC and with OSC.

Influence of soil scarification on reindeer foraging and damage to planted Pinus sylvestris seedlings

Abstract The effects of soil scarification on reindeer lichen cover and re-establishment, reindeer foraging and damage possibly caused by reindeer to planted Scots pine seedlings were studied during six growing periods in a field experiment established in a reindeer lichen site that was grazed by a herd of 500–600 reindeer each winter. Seedlings (at a density equivalent to 2000 ha−1) were planted in mounds with mineral soil on top, in tracks with exposed mineral soil, in tracks with mixed organic material and mineral soil and in intact lichen mat (control) with no soil disturbance. The disturbed area varied from 0 to 28%. After six growing periods, the reindeer lichen cover and volume were 10–20% lower in the scarified plots than in the control plots. There was no clear evidence that the reindeer avoided foraging even in plots with the highest levels of soil disturbance. However, the behaviour of the reindeer during winter grazing seemed to be affected by both coverage of reindeer lichen (positively) and the proportion of exposed mineral soil (negatively). Damage possibly caused by reindeer trampling affected 8.2% of the living seedlings each year and approximately 50% of these seedlings were subsequently infected by fungal diseases (compared with 20% of viable undamaged seedlings). Scarification treatments that exposed mineral soil mildly resulted in higher survival and growth rates than the other treatments, especially the control.

Mechanizsed microsite preparation and direct seeding of Pinus sylvestris in boreal forests — a way to create desired spacing at low cost

The main objective of this study was to examine the cost, flexibility, and appropriate scale of mechanized microsite preparation (MP), in combination with mechanical direct seeding of Pinus sylvestris L. with orchard seed. This technique was tested at four boreal forest sites in Northern Sweden. Orchard and stand seeds were sown with and without MP. The use of orchard seed increased seedling establishment by 41% and the use of MP increased seedling establishment by 47%, respectively, after two years. The best substrates for sowing when using MP were OAh-, E- and BC-horizon, in ranked order. The use of orchard seed compared to stand seed increased mean seedling height by 25% after four years. These trials suggest that to obtain a density of 5,000 stems ha-1 four years after seeding, 61,000 viable stand seeds or 41,000 orchard seeds ha-1 should be sown if MP is not used. If MP is used, seeding rate could be reduced by about 32%. By using MP, and by further improving scarification technique so that all scarified area is thin OAh-horizon, we predict that only 32,000 stand seeds or 22,000 orchard seeds ha-1, i.e., half the dosage, should be needed. Under these optimal conditions, it would be necessary to sow about six and four germinable stand and orchard seeds, respectively, to ensure one seedling after four years. Furthermore, regeneration cost would be less than a third that of planting.

Pinus contorta growth in northern Sweden as affected by soil scarification

The aim of this study was to quantify the effects of different soil scarification methods on tree growth. Soil scarification influenced stem volume and stem biomass yield of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) in a 17-year-old field trial in boreal Sweden. Soil scarification (disc trenching, mounding and ploughing) resulted in an average stem volume yield of 3.1 and 34.2 m3 ha−1 on the poor and intermediate sites, respectively, while corresponding values for no soil scarification were 0.9 and 16.7 m3 ha−1. In comparison to no scarification, ploughing increased volume yields by 500% on the poor site and by 200% on the intermediate sites. The ranking according to stem volume yield was ploughing > disc trenching = mounding ≥ no soil scarification. Averaged over the two sites, the mean annual increment of stem biomass was 219% and 145% higher (in d.w., 0.26 kg and 0.34 kg per sample tree) after ploughing compared with no soil scarification, for the average and dominant sample trees, respectively. Although not significant, the increased growth rate after soil scarification decreased the average stem basic wood density of the sample trees with 1.6% and 5.3%, at the poor and intermediate sites, respectively. In conclusion, soil scarification significantly increased the 17-year stem volume yield compared with no scarification. The results also indicate that the difference in stem biomass yield between ploughing and the other methods, especially no soil scarification, will increase even more in the near future.

Characterization of Scots pine stump-root biomass as feed-stock for gasification.

The main objective was to explore the potential for gasifying Scots pine stump-root biomass (SRB). Washed thin roots, coarse roots, stump heartwood and stump sapwood were characterized (solid wood, milling and powder characteristics) before and during industrial processing. Non-slagging gasification of the SRB fuels and a reference stem wood was successful, and the gasification parameters (synthesis gas and bottom ash characteristics) were similar. However, the heartwood fuel had high levels of extractives (≈19%) compared to the other fuels (2-8%) and thereby ≈16% higher energy contents but caused disturbances during milling, storage, feeding and gasification. SRB fuels could be sorted automatically according to their extractives and moisture contents using near-infrared spectroscopy, and their amounts and quality in forests can be predicted using routinely collected stand data, biomass functions and drill core analyses. Thus, SRB gasification has great potential and the proposed characterizations exploit it.

Compression Processing and Load Compression of Young Scots Pine and Birch Trees in Thinnings for Bioenergy

Abstract In many boreal countries forest biomass from dense young stands has great potential to meet growing demands for bioenergy. However, there is currently no cost-effective operational system for harvesting such stands. When harvesting, it would be desirable to compress trees and leave some of the foliage and fine branches in the stand in order to reduce extraction of nutrients and improve the harvested material’s fuel properties from a reduced ash content point of view. The objectives were to evaluate experimental systems (a boom-tip mounted unit for processing bunches, and a small prototype forwarder for compressing loads) in terms of their utility for compressing and partially debranching fresh and stored bunches of Scots pine trees and compressing forwarder loads of fresh Scots pine and birch trees. Processing of fresh bunches resulted in mass losses of about 10% (dbh-class 5–8 cm; not significant) to 15% (dbh-class 12–15 cm; significant) with 35 to 50% reductions in ash contents and increases in bulk and net energy density of about 80 to 160%. In-stand storage of bunches before processing generally yielded no significant advantages except for a 10%-unit reduction in moisture content. Compression of forwarder loads resulted in 16 (pine) to 32% (birch) increases in load densities, with a significant increase for birch trees. The described techniques facilitate productivity increases of off-road and road transport of tree parts, and a substantial proportion of the ash-rich materials such as needles and fine branches are left in the stand. If both tested techniques are applied during the harvesting of young trees the benefits would be substantial.

Pyramidal indentations as a microsite preparation for direct seeding of Pinus sylvestris L.

Four field experiments are described in which Scots pine (Pinus sylvestris L) seed was sown in indentations made by pyramidal tools of different form (square base = 4 cm; angles from 44 to 90°; dep...

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.

Long-term effects on growth and yield of corridor thinning in young Pinus sylvestris stands

Abstract Corridor thinning can be an efficient method for extracting biomass from young stands, but its effects on subsequent productivity are uncertain. Therefore, its long-term effects were studied, using data obtained from two pre-commercial thinning (PCT) experiments (over 28 years) and nine thinning experiments (over 22 years). In the PCT experiments, thinning with total corridor areas of 0 (control), 57, 65, 73, 79 and 82% were compared to selective PCT leaving 1000 and 1400 stems/ha. In the thinning experiments corridor thinning (50% corridor area) and selective thinning from below (50% of basal area) were compared. No significant differences in diameter at breast height (DBH) were found between the corridor PCT and control treatments, but the control resulted in approximately 28–83% higher standing volumes/ha than the PCT treatments. Corridor PCT and thinning treatments resulted in higher stand stem density and lower mean DBH than selective treatments. No significant differences in volume growth, standing volume, mortality volume or height growth were detected between selective and corridor thinning or between most of the PCT treatments. The findings indicate that relatively large amounts of biomass could be extracted schematically, by early thinning instead of PCT, in young Scots pine stands without significant future yield losses.