Bjørn Tveite

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(+47) 903 65 583
bjorn.tveite@nibio.no

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Ås - Bygg H8

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Høgskoleveien 8, 1433 Ås

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Sammendrag

This study compares the responses of two Swedish 5-year predictive stand-level functions with the observed responses in 721 fertilization experiment plots in Norway fertilized with nitrogen (N). All plots are single-species consisting of Norway spruce (Picea abies (L.) H. Karst.) or Scots pine (Pinus sylvestris L.) fertilized with ammonium nitrate (AN) or urea. The correlations between the observed and the two predicted responses were 0.34–0.40 for all plots taken together. One response function performed well on average, but underestimated the response in pine plots and overestimated the response in spruce plots. The second function overpredicted the response on the full dataset, in spruce plots and old forest, but performed well in pine plots. Both functions overestimated the growth response in high-productive plots. Higher N deposition in Norway than in Sweden may count for parts of the deviations. Testing of fertilization functions on new datasets is rare, but important part of the evaluation of functions. As the functions are not well fit for predicting the growth response in spruce and high-productive plots in our sample, new functions that include N deposition are welcome.

Sammendrag

The relative volume growth effects of thinning after whole-tree harvesting (WTH) compared to a conventional stem-only harvest (CH) in young stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) were analyzed, using a series of four pine and four spruce field experiments. The series was established in the years 1972–1977, and thinning was performed only once. Results are shown periodically and cumulatively. All sites were included for 20 (19) years in pine and 25 years in spruce. The total experimental period varied between 19 and 35 years for individual sites. Four models assuming additive or multiplicative effects gave only slightly varying results. The inclusion of standing volume after thinning as a covariate was effective in spruce independent of whether the covariate was treated as multiplicative or additive. A logarithmic model with a multiplicative effect of the covariate was preferred in further presentations. Results for pine stands after 20 years indicated a nonsignificant loss of 5% with confidence limits (p = 0.05) of ±6–7%, while the spruce stands showed a significant growth loss of 11% with confidence limits of ±4–5% after 25 years. The difference between the species in relative growth effects was significant, and amounted to 8% for a cumulative 20-year period. No indications of trends in response were found during a 20-year period in pine and a 25-year period in spruce. An analysis of growth effects in the first years showed that basal area increment in spruce was significantly reduced already in the first growing season after thinning.

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The aim of this study was to determine the effect of whole-tree harvesting (WTH) on the growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as compared to conventional stem harvesting (CH) over 10 and 20 years. Compensatory (WTH+ CoF) and normal nitrogen-based (CH + F or WTH+ F) fertilisation were also studied. A series of 22 field experiments were established during 1977–1987, representing a range of site types and climatic conditions in Finland, Norway and Sweden. The treatments were performed at the time of establishment and were repeated after 10–13 years at 11 experimental sites. Seven experiments were followed for 25 years. Volume increment was on average significantly lower after WTH than after CH in both 10-year periods in the spruce stands. In the pine stands thinned only once, the WTH induced growth reduction was significant during the second 10-year period, indicating a long-term response. Volume increment of pine stands was 4 and 8% and that of spruce stands 5 and 13% lower on the WTH plots than on CH during the first and the second 10-year period, respectively. For the second 10- year period the relative volume increment of the whole-tree harvested plots tended to be negatively correlated with the amount of logging residue. Accordingly, the relative volume increment decreased more, the more logging residue was harvested, stressing the importance of developing methods for leaving the nutrient-rich needles on site. If nutrient (N, P, K) losses with the removed logging residues were compensated with fertiliser (WTH+ CoF), the volume increment was equal to that in the CH plots. Nitrogen (150–180 kg ha−1) or N+ P fertilisation increased tree growth in all experiments except in one very productive spruce stand. Pine stands fertilised only once had a normal positive growth response during the first 10-year period, on average 13m3 ha−1, followed by a negative response of 5m3 ha−1 during the second 10-year period. The fertilisation effect of WTH+ F and WTH+ CoF on basal area increment was both smaller and shorter than with CH+ F.

Sammendrag

The use of logging residues for bioenergy is encouraged in many countries, due to an increasing demand for renewable energy. However, there is concern that removal of logging residues may cause a long-term reduction in soil nutrient availability, reducing forest growth in the remaining stand. To quantify the growth response of Norway spruce and Scots pine to whole-three harvesting at first thinning a series of eight field experiments was set up in SE Norway in the seventies. Results after 25 years showed that whole-tree thinning lead to a decrease in forest growth. The effect was present more or less immediately after thinning, and was still present after 25 years. The average reduction in growth was around 10 % after 25 years in the spruce stands, while in the pine stands a non-significant average growth reduction of 4 % was found. The results are generated under experimental conditions, and in practice a share of the residues is left on site, decreasing the nutrient loss.

Sammendrag

The objective of this study was to quantify the long-term growth response of Norway spruce and Scots pine to whole-three harvesting (WTH) at first thinning. The results show that for spruce, WTH has lead to a decrease in forest growth 25 years after thinning. In the pine stands, the results were more variable between sites and periods and the growth reduction after 25 years was not statistically significant.

Sammendrag

High-frequency variation of Norway spruce radial increment [Picea abies (L.) Karst.] and its dependence on various climatic variables was compared in stands across latitudinal and altitudinal transects in southwestern and eastern Germany, Norway, and Finland. The tested variables included local temperature and precipitation, northern hemisphere temperature anomalies, and the climatic teleconnection patterns (North Atlantic Oscillation, East Atlantic, East Atlantic Jet, East Atlantic/West Russia, and Scandinavian patterns). Climatic impact on radial increment increased towards minimum and maximum values of the long-term temperature and precipitation regimes, i.e. trees growing under average conditions respond less strongly to climatic variation. Increment variation was clearly correlated with temperature. Warm Mays promoted radial increments in all regions. If the long-term average temperature sum at a stand was below 1,200-1,300 degree days, above average summer temperature increased radial increment. In regions with more temperate climate, water availability was also a growth-limiting factor. However, in those cases where absolute precipitation sum was clearly related to radial increment variation, its effect was dependent on temperature-induced water stress. The estimated dates of initiation and cessation of growing season and growing season length were not clearly related to annual radial increment. Significant correlations were found between radial increment and climatic teleconnection indices, especially with the winter, May and August North Atlantic Oscillation indices, but it is not easy to find a physiological interpretation for these findings.

Sammendrag

Regional and temporal growth variation of Norway spruce (Picea abies (L.) Karst.) and its dependence on air temperature and precipitation were compared in stands across latitudinal and altitudinal transects in southwestern and eastern Germany, Norway, and Finland.The temporal variation of radial growth was divided into two components: medium- and high-frequency variation, i.e. decadal and year-to-year variation, respectively. The medium-frequency component was rather different between regions, especially the southern and northern ones. However, within each region the medium-frequency growth variation was relatively similar, irrespective of altitudinal and latitudinal differences of the sample sites.A part of the high-frequency variation was common to all four regions, which suggests that some factors synchronising tree growth are common for the entire study area. The high-frequency component of growth was more strongly related to monthly air temperature and precipitation than was the medium-frequency variation. The limiting effect of low temperatures was more significant at northern as well as high-altitude sites, while the importance of precipitation increased in the south and at low altitudes.

Sammendrag

Relationships between crown density and growth of Norway spruce stands are presented, after removal of the effects of major natural influences. On 569 monitoring plots comprising 40 000 trees, crown density has been annually assessed during 1991 to 1996.Stand growth was determined from measurements of diameter and height in 1991 and in 1996. Various models explaining mean crown density and annual growth of the stands as a function of natural factors, like age and site index, were compared.The influence of the natural factors were then removed by recalculating crown density to residual values from one preferred model, and by recalculating growth to relative values given in percent of model predictions.Crown density and its residuals were positively correlated to growth. These relationships were weak in terms of their ability to explain variation (low R2). However, the various relationships consistently indicated that roughly 1% change in crown density corresponded to 1% change in growth. This relationship also included common spatial variation over Norway: a large part of southeast Norway had unexplained low crown density and unexplained low growth.Some other, smaller regional consistencies were found as well. The study supports the use of crown density assessments, and further it encourages the use of growth data in the search for major stress factors responsible for present forest condition.

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Rapporten er en analyse av resultater fram til 1998 fra det første store tynnings-forsøket i granskog som ble anlagt i 1958. Høydeutviklingen følger bonitetskurvene godt gjennom hele forsøksperioden. Middeldiameteren av alle trærne øker med økende tynningsstyrke, og totalproduksjonen synker med økende tynningsstyrke. Innen området S% 10 til S% 20 synker totalproduksjonen ca 5%. Middeldiameteren av de 600 grøvste trærne per ha (D6) var 1,9 cm større i sterk tynning enn i kontrollen i 1998. I løpet av forsøksperioden har forskjellen i diameterøkning mellom kontrollen og sterk tynning vært 0,4 mm per år. Fortsetter samme forskjell i økning vil D6 ved antatt foryngelseshogst om 25 år bli 2,9 cm større i sterk tynning enn i kontrollen. 1998 var gjennomsnittlig volum av stående trær 416 m3 per ha i kontrollen og 266 m3 per ha i sterk tynning. Den naturlige avgangen i kontrollen har vært 40 m3 per ha eller 8.8 % av totalproduksjonen. Diametertilvekstfunksjonene som er benyttet i prognosemodellene for gran overvurderer tilveksten noe for alle behandlingene i dette forsøket. Dimensjonsfordelingen viser at det også i kontrollen, der det i 1998 fremdeles sto 2230 levende trær per ha, er utviklet mange store trær. Dimensjonsfordelingen, beregnet etter funksjoner (Holte 1993), er testet mot kontrollen og mot sterk tynning, og viser en god overensstemmelse for kontrollen. For sterk tynning undervurderes tynningseffekten for midlere dimensjoner, mens effekten for de største dimensjonene overvurderes. Diametertilvekstfunksjonene, dimensjonsfordelingsfunksjonene og bonitetsfunksjonene som er grunnlaget for dagens prognoseverktøy, stemmer rimelig bra med resultatene fra dette forsøket. Volumet av de 600 grøvste trær per ha i 1998 (V6), var 19 % større i sterk tynning enn i kontrollen. Sterk tynning har noe større høydebonitet enn kontrollen. Tynningsstyrkene ”svak” og ”middels” har ikke økt volumet av de 600 grøvste trærne per ha sammenlignet med kontrollen. Med gjeldende tømmerpriser og driftskostnader for de aktuelle diameterklasser, er slakteverdien av kontroll og sterk tynning beregnet. Slakteverdien for kontrollen er ca 24 000 kr større enn for sterk tynning. Slakteverdien er størst for det trerike bestand med størst volum, selv om sterk tynning har flest trær som er større enn 22 cm. Dette betyr at dersom tynningene i dette forsøket ikke har gitt et nettobidrag på 24 000 kr, hensyn tatt til renteeffekten, vil også nåverdien av kontrollen være størst. En vurdering av driftsnettoen for tynningsuttakene med sterk tynning viser at for å nå 24 000 kr må driftskostnadene ved tynning være den samme som ved snauflatehogst for samme dimensjon, noe som er lite realistisk under dagens vilkår. Ved vurdering av resultatene bør det legges vekt på at tettheten før første tynning i dette forsøket var ca 5000 trær per ha. Med dagens skogskjøtsel, der det etter ungskogpleie anbefales å fristille mindre enn halvparten av dette treantallet, vil effekten av videre tynning måtte bli mindre.

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Forsøket som er analysert ligger i et plantet granbestand på bonitet G17. I 1999 var totalalderen 50 år og overhøyden ca 17 meter. Forsøket belyser effektene av at treantallet ble redusert fra ca 3000 trær per ha til henholdsvis 2070-1600-1100 og 820 trær per ha da overhøyden var ca 5 meter og totalalderen var 22 år. I 1999 øker middeldiameteren (Dg) med avtagende treantall fra 14,9 cm til 19,3 cm. Forskjellen på Dg mellom forsøksledd 2070 og 820 er 4,4 cm. Volum av stående trær avtar med synkende treantall, og varierer i 1999 mellom 229 m3 og 177 m3 per ha. Størrelsen av naturlig avgang er påvirket av tettheten. I 1999 er samlet avgang 11,7 m3 per ha i forsøksledd 2070 og 2,5 m3 per ha i forsøksledd 820. Naturlig avgang er både absolutt og relativt sett størst i de tetteste forsøksledd. Totalproduksjonen avtar med avtagende treantall. Forskjellen mellom forsøks-leddene 2070 og 820 i 1999 er 61 m3 per ha, eller 25 % av totalproduksjonen i ledd 2070 . De grøvste trærne har hatt den største diametertilveksten i alle forsøksledd. Økningen av diametertilveksten er størst for de største trærne. Diametertilveksten har økt mest i forsøksledd 820 og minst i forsøksledd 2070. Middeldiameteren av de 800 grøvste trærne per ha (D800) i 1999 er 1,4 cm større i forsøksledd 820 enn i forsøksledd 2070. Diameteren av de 100, 400 og de 800 grøvste trærne i 1999, dvs D100, D400 og D800, er sammenlignet med beregnede verdier etter Pettersson ( 1993). Funksjonen overvurderte den virkelige diameteren, men forskjellene var, unntatt i et ett tilfelle, mindre en 1 cm. Forskjellen mellom D800 i forsøksledd 2070 og i forsøksledd 820 beregnet med Petterssons funksjoner er 2,3 cm i 1999 og 1,9 cm i 1989, mens den virkelige forskjellen i forsøket var henholdsvis 1,4 cm og 0,9 cm. Generelt viser testen at treantallsreduksjonen øker diameterveksten på de grøvste trærne innen bestand i samme grad i vårt forsøk som i de forsøk Pettersson (1993) har benyttet. Grunnflatemiddelstammens diametertilvekst samsvarer med tilvekstfunksjon (Blingsmo 1984) brukt i norske produksjonsmodeller. Volumet av de 800 grøvste trærne avtar noe med økende treantall. Forskjellen mellom forsøksleddene 2070 og 820 i 1999, 28 år etter uttak, er 19 m3 per ha. Kronehøyden på de 800 grøvste trærne varierer i 1999 fra 2,7 m til 4,5 m, og øker med synkende treantall. I forsøksledd 820 er kronehøyden på de 800 grøvste trærne 1,75 meter lavere enn i forsøksledd 2070. Kvisttykkelsen øker med avtagende treantall, med treets diameter, og med økende høyde i det undersøkte området opp til ca 5 meter over marken. For kvister mellom 2,5 og 5 meter fra marken er forskjellen i kvisttykkelse i 1995 3,7 – 4,0 mm mellom forsøksledd 2070 og forsøksledd 820. Mellom forsøksledd 2070 og 1600 er forskjellen bare 1,2 - 1,5 mm, og mellom forsøksledd 1600 og 1100 bare 1,2-1,6 mm. Forskjellene mellom forsøksledd vil kunne øke noe, fordi det ennå er en større andel levende kvister i forsøksleddene med lave treantall.