| 1. |
- Ratke, Christine, et al.
(author)
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Downregulating aspen xylan biosynthetic GT43 genes in developing wood stimulates growth via reprograming of the transcriptome
- 2018
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In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 219:1, s. 230-245
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Journal article (peer-reviewed)abstract
- Xylan is one of the main compounds determining wood properties in hardwood species. The xylan backbone is thought to be synthesized by a synthase complex comprising two members of the GT43 family. We downregulated all GT43 genes in hybrid aspen (Populus tremulaxtremuloides) to understand their involvement in xylan biosynthesis.All three clades of the GT43 family were targeted for downregulation using RNA interference individually or in different combinations, either constitutively or specifically in developing wood.Simultaneous downregulation in developing wood of the B (IRX9) and C (IRX14) clades resulted in reduced xylan Xyl content relative to reducing end sequence, supporting their role in xylan backbone biosynthesis. This was accompanied by a higher lignocellulose saccharification efficiency. Unexpectedly, GT43 suppression in developing wood led to an overall growth stimulation, xylem cell wall thinning and a shift in cellulose orientation. Transcriptome profiling of these transgenic lines indicated that cell cycling was stimulated and secondary wall biosynthesis was repressed. We suggest that the reduced xylan elongation is sensed by the cell wall integrity surveying mechanism in developing wood.Our results show that wood-specific suppression of xylan-biosynthetic GT43 genes activates signaling responses, leading to increased growth and improved lignocellulose saccharification.
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| 2. |
- Ulvcrona, Kristina, et al.
(author)
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Identifying the biological effects of pre-commercial thinning on diameter growth in young Scots pine stands
- 2014
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In: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 29, s. 427-435
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Journal article (peer-reviewed)abstract
- Data from seven Scots pine (Pinus sylvestris L.) stands in central Sweden that had undergone pre-commercial thinning (PCT) were used to investigate the biological effect of PCT on the diameter at breast height (DBH) growth of the remaining trees. Two treatments were considered: a PCT treatment and a control (C) with no PCT. The DBH of the trees in each stand was measured on up to four occasions over 15 years. We examined mean DBH and DBH growth of the largest 300, 600, 900 and 1200 trees ha-1. Two methods of selecting the trees used to calculate the mean DBH values for each measurement occasion were considered: the actual mean DBH (Dma), which is based on the DBH distribution of the trees on the measurement occasion in question, and the genuine mean DBH (Dmg), which is based on the DBH distribution of the trees on the final measurement occasion of the study and therefore focuses on the same set of trees for all measurement occasions. There was no clear difference between the Dma- and Dmg-based DBH increments, but the Dmg values tended to be somewhat larger both for the C and PCT treatments. Over a 15-year period, the relative mean yearly increments (Dma/Dmg) for different tree size classes ranged from 0.91 to 0.98, with lower values for the C treatment and larger DBH size classes. We found that PCT promotes DBH growth: over a 15-year period, the increased growth amounted to about 2.0 mm year-1 compared to the trees in unthinned plots.
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| 3. |
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| 4. |
- Ulvcrona, Kristina, et al.
(author)
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Stand density and fertilization effects on aboveground allocation patterns and stem form of Pinus sylvestris in young stands
- 2014
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In: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 29, s. 197-209
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Journal article (peer-reviewed)abstract
- The increasing demand for forest biomass for energy generation could be partially met by growing denser stands and use of fertilizer. Before this is done at large scale, more knowledge of the effects of stand density and fertilization on aboveground allocation patterns and stem form is needed. Therefore, effects of pre-commercial thinning (PCT) to 3000 stems ha(-1), an unthinned dense control (C), and PCT combined with two levels of fertilization (100 kg ha(-1) of nitrogen applied either during the establishment of the field experiment (F1) or annually (F2)) were examined in 23- to 26-year-old Scots pine (Pinus sylvestris L.) stands six years after the establishment of the field experiment. In total, 114 sample trees were harvested using destructive biomass sampling. The growth allocation and stem form of trees with diameter at breast height (DBH; 1.3 m height) >5.0 cm were not affected by either the PCT or fertilization. Small trees (DBH < 5 cm) in denser, unthinned control plots had more slender stems (lower DBH/height ratios) and allocated less growth to branches and foliage than trees in PCT plots. Fertilization had little effect on the stem form and growth allocation of the smallest trees. Therefore, effects of stem density and fertilization on stem form and growth allocation to foliage were only found for small suppressed trees, and the treatments had very little influence on dominant and codominant trees.
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| 5. |
- Ulvcrona, Kristina, et al.
(author)
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The Effect of Intensive Fertilization of Height Development in Young Unthinned Scots Pine (Pinus Sylvestris L.) Stands
- 2011
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In: Rapport fra Skog og landskap. - 1891-7933. ; , s. 49-50
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Conference paper (other academic/artistic)abstract
- Demands for forest biomass, mainly for use as biofuels and energy generation, have been rising for several years. Growth of trees are affected by environmental factors. For example, competition for light affects the allocation of growth along the stem, and competition for water and / or nutrients affects the overall growth rate [1, 2, 3, 4]. However, few studies have been investigating the effect of intensive fertilization on height development in young unthinned stands. Therefore the aim of this study was to determine the principal effect of fertilization on height development in young Scots pine trees (Pinus sylvestris L.). The hypothesis being that Scots pine trees from intensively fertilized unthinned stands have a higher both absolute and relative hight development than trees from unfertilized unthinned stands. Within this study, in all 101 trees from three field trials in Northern Sweden, investigating fertilization and spacing in young Scots pine dominated stands, were felled and measured. 68 trees from the unthinned treatment and 33 trees from the unthinned intensively fertilized treatment (100 kg ha-1 annually from 1997 onwards). Total height in spring 2009 and annual height growth ( topp shoot) for the years between 1999 and 2008 were measured with measuring tape. All investigated trees were within the same range of height in year 1999. Differences regarding total height year 2008, mean height year 1999 and annual height growth for years 2000 - 2008 were analyzed with standard GLM procedure. Used model was "site" and "treatment". Significantly higher total height increment was found for the intensively fertilized treatment during the investigated period. Fertilized trees had a 3% higher mean height (5.3 m) than unfertilized trees (5.2 m) at the start in the year 1999. After the growing season year 2008 fertilized trees mean height (9.45 m) was 12% higher than unfertilized trees (8.53 m).Generally during the period, the fertilized trees expressed both higher total and relative annual height increment than the control (Figure 1). Figure 1. Development of relative annual height increment for unfertilized (C) and intensively fertilized (c+F2) sites between years 2000 to 2008. The figure clearly describes both the overall trends that fertilization generally increases relative annual height when compared to control and that the difference in relative increment is higher during the first years of intensive fertilization than later in the cycle. Fertilized trees showed significantly higher relative height increment during all years except for the last year 2008 when the relative increment was the same as for unfertilized trees. Note that the fertilized trees then was significantly higher than unfertilized trees. In absolute values differences between treatments regarding height increment varied between 17% and 28%. Site had significant effect on relative height increment during the years 2000, 2002 - 2003 and 2005 - 2006. No apparent trend could be found explaining this when examining individual tree and site variables. However, variable site was not significant during years 2007 and 2008 when also the difference in relative height increment was the smallest. Total height and relative increment was as described above significantly higher in fertilized trees when compared to unfertilized thus supporting the hypothesis. Both the absolute and relative difference between treatments was largest in the beginning of the studied period and then generally decreased over time. This pattern indicates that the studied net effect of the intensive fertilization on height development is a result of interactions not included in this study. This is interesting and in need of further studies since the literature describing these and other related growth factors in very young dense stands is sparse. The effect of site was significant in only 5 of the 9 years included within the study. Probably will future studies using the combination of this type of data together with information concerning climatic and soil interactions be useful for development of more knowledge regarding tree and stand height development. Many studies have been investigating height development in young stands in relation to pre-commercial thinning and recent studies include those by [5] and [6]. The general conclusion from these and earlier studies is that the mean height is likely to decline with higher stem densities due to a higher number of suppressed trees in the stand. The results presented here indicates that fertilization is a treatment that increases site index and thus might allow development of silvicultural management schedules that can use higher stem densities without as pronounced negative effects on stand height development. 1 Cannell, M.G.R., Rothery, P. & Ford, E.D. 1984 Competition within stands of Picea sitchensis and Pinus contorta. Ann. Bot. 53: 349-362. 2 Nilsson, U. and Albrektson, A. 1993 Productivity of needles and allocation of growth in young Scots pine trees of different competitive status. For. Ecol. Manag. 62: 173-187. 3 Nilsson, U. and Gemmel, P. 1993 Changes in growth and allocation of growth in young Scots pine and Norway spruce due to competition. Scand. J. For. Res. 8(2): 213-223. 4 Nilsson, U. 1994 Development of growth and stand structure in Norway spruce stands planted with different initial densities. Scand. J. For. Res. 9: 135-142 5 Ruha, T. and Varmola, M. 1997 Precommercial thinning in naturally regenerated Scots pine stands in Northern Finland. Silva Fenn. 31(4): 401-415. 6 Varmola, M. and Salminen, H. 2004 Timing and intensity of pre-commercial thinning in Pinus sylvestris stands. Scand. J. For. Res. 19: 142-151.
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| 6. |
- Ulvcrona, Kristina, et al.
(author)
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Tree mortality in Pinus sylvestris stands in Sweden after pre-commercial thinning at different densities and thinning heights
- 2011
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In: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 26, s. 319-328
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Journal article (peer-reviewed)abstract
- Individual tree mortality was analysed for 9924 Scots pine trees from 26 pre-commercial thinning (PCT) experiments established in Sweden (57 degrees-66 degrees N) between 1953 and 1972. Almost all of the stands examined were naturally regenerated and homogenous pine stands. The PCT treatment factors included stand density and height at the time of PCT. The stand densities varied between 600 stems ha -1 and 9000 stems ha -1 before PCT. The height at the time of PCT varied between 1 and 8 m and mortality was examined 8.6-23.5 years after PCT. The results showed low overall mortality (5%) irrespective of treatment. Mortality was higher in stands with high stem number before PCT than in stands with low pre-PCT stem number. In addition, higher mortality was associated with early PCT (heights below 4 m) than with late PCT (heights above 4 m). Mortality after PCT was not clearly correlated to stand densities; the highest mortality was found for stand densities of 0-700 stems ha -1 and the lowest for 700-1500 stems ha -1. Furthermore, mortality was higher for small trees than for average height or tall trees. The main conclusion from this study, therefore, was that timing of PCT and thinning grade has only marginal effects on the risk of mortality.
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| 7. |
- Ulvcrona, Thomas, et al.
(author)
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The effects of pre-commercial thinning and fertilization on characteristics of juvenile clearwood of Scots pine (Pinus sylvestris L.)
- 2011
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In: Forestry. - : Oxford University Press (OUP). - 0015-752X .- 1464-3626. ; 84, s. 207-219
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Journal article (peer-reviewed)abstract
- As a result of escalating demands for wood and parts of trees for use as biofuels and energy generation, there is growing interest in increasing forest biomass production. The objective of this study, therefore, was to investigate whether the physical properties and modulus of elasticity (MOE) of Scots pine (Pinus sylvestris L.) juvenile clearwood change in response to different silvicultural treatments (pre-commercial thinning and fertilizer application) in 22- to 25-year-old trees. We achieved this by measuring short-term mechanical properties and using X-ray densitometry. The results show that the MOE and latewood density were not affected by any treatment. The earlywood density and the percentages of earlywood and latewood were affected by the treatments. Fertilization increased ring width and the percentage of earlywood but decreased the percentage of latewood. Pre-commercial thinning also increased ring width and the percentage of earlywood, and decreased the percentage of latewood, but did not affect earlywood density. Furthermore, our results suggest that the MOE of wood is not affected by the different treatments as long as the cambial age and ring width are the same and that fertilization should be considered as a factor that increases the site index where intra-ring properties are concerned.
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| 8. |
- Bergström, Dan, et al.
(author)
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Skörd av skogsbränsle i förstagallringar
- 2010
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Reports (other academic/artistic)abstract
- Efterfrågan på skogsbränslen ökar men någon större ökning av biprodukter från skogsindustrin kan man inte räkna med de kommande 10-20 åren. Detta innebär att konkurrensen om veden kommer att intensifieras och man ser idag möjligheter att skörda skogsbränslen från skogen, i såväl gallringar som föryngringsavverkningar. I Sverige utgör ogallrade skogar med en höjd under 15 m och ett biomassainnehåll mer än 30 ton torrsubstans (TS) per ha cirka 18,4% av den totala skogsmarksarealen. Den totala stående volymen på dessa arealer är cirka 258 miljoner ton TS varav 56% finns i Norrland. Den årliga avverkningspotentialen från dessa skogar ligger på ca 5 miljoner ton TS (ca 23 TWh) för landet som helhet. Vid en konventionell förstagallring tar man ut massaved (och ev. klentimmer) som gagnvirke där endast stammar med en brösthöjdsdiameter (dbh) över cirka 8 cm är kommersiellt gångbara. I tidiga förstagallringar får den konventionella gallringen höga avverkningskostnader på grund av beståndets låga medelstam (dbh < 12cm) och låg andel gagnvirke. Generellt när man apterar massaved i tidiga gallringar så kan cirka 20-30% av stamvedsvolymen inte användas pga för klena dimensioner. Denna volym tillsammans med trädets topp och grenar, lämnas outnyttjade i beståndet. Idag med en växande skogsbränslemarknad finns ett nytt sortiment som kan konkurrera med rundvirket i förstagallringar av stamrika, klena bestånd. Syftet med denna studie är att påvisa de mängder skogsbränsle som faller ut vid gallring av typiska klena, täta och normala gallringar i södra Sverige och att jämföra detta med rundvirkesutfallet som samma bestånd kan generera vad avser mängder och lönsamhet vid olika prisrelation mellan sortimenten. I utförda beräkningar har typbestånd använts. Ett relativt högt massavedspris och ett relativt lågt skogsbränslepris jämfört dagens prisnivåer har använts. Resultaten visar att skogsbränsle kan ge uppemot tre gånger högre bruttointäkt per hektar än massaved i ”klena” (dbh 9 cm) bestånd. Även i en mer normala förstagallring vad gäller stamdiametern (dbh 14 cm) ger skogsbränslet ca 13% högre bruttointäkt. I beräkningarna uppvisar skogsbränsle systemet ett avsevärt högre nettointäkt än massavedssystemet i det ”klena” beståndet. Författarna konkluderar att: • i tidiga/klena gallringar utgör den potentiella mängden massaved endast en liten del av den totala biomassan vilket också ger ett förhållandevis låg bruttointäkt jämfört med om hela biomassan skördas som skogsbränsle; • inte ens i ”normala” förstagallringar är bruttointäkten på massaveden högre än för skogsbränsle med dagens prisnivåer; • i klena” förstagallringar ger skogsbränsleskörd ett betydligt högre nettointäkt än motsvarande massavedsskörd; • om anpassad teknik för skörd och hantering av klena träd utvecklas kan stora mängder bränsle kostnadseffektivt skördas från de svenska ungskogarna. Det är inte något stort tekniksprång som behövs, och med kloka satsningar kan nya system realiseras inom kort tid
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| 9. |
- Fredriksson, Maria, et al.
(author)
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Microclimate and moisture content profile measurements in rain exposed Norway spruce (Picea abies (L.) Karst.) joints
- 2016
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In: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 11:4, s. 189-200
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Journal article (peer-reviewed)abstract
- In order to perform service life predictions of rain exposed wood structures, the moisture and temperature conditions in the structure need to be known as well as which degradation that occurs under those exposure conditions. The microclimate (the moisture conditions at the surface) is the boundary condition for moisture transport into the wood and depends on the detail design; joints between two pieces of wood can act as a water trap which give long durations of surface moisture after rain events and hinders drying. This study presents moisture content and microclimate measurements in three types of Norway spruce joints exposed to artificial rain in the laboratory. Both the microclimate (the duration of water on surfaces and in gaps) and the moisture content profiles were monitored. The microclimate was changed by changing the size of the gap between the two boards. The duration of water in the gap depended both on the gap size and on the permeability of the wood (sapwood/heartwood, end grain surface/side grain surface). In many cases, a larger gap width gave shorter durations of high moisture contents since a larger gap gave more favourable drying conditions, but the magnitude of this reduction varied between joint types.
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| 10. |
- Fredriksson, Maria, et al.
(author)
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Moisture sorption and swelling of Norway spruce [Picea abies (L.) Karst.] impregnated with linseed oil
- 2010
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In: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 5:3 & 4, s. 135-142
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Journal article (peer-reviewed)abstract
- The moisture sorption and swelling of spruce specimens impregnated with linseed oil and unimpregnated controls were studied in two sorption experiments: from 0 to 55% relative humidity (RH) and from 55% RH to water saturation. Sorption isotherms were also determined using a sorption balance. The impregnated specimens had lower rates of both moisture sorption and swelling than the unimpregnated controls; however, there was no significant difference in final moisture contents. In addition, the linseed oil impregnation did not improve the dimensional stability of the wood; in most cases the specimens impregnated with linseed oil swelled more than the unimpregnated controls. For the impregnated specimens, reductions in swelling rates were in most cases seen without corresponding reductions in final swelling. The moisture sorption rate was reduced for the impregnated specimens but there were generally no reductions in equilibrium moisture content.
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