Publikasjoner
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1989
Forfattere
Sverre SkoklefaldSammendrag
The experimental area is situated in southeast Norway (1119\" E.Gr., 6055\" N.), about 500 m above sea level (Fig. 1). Eu-Piceetum myrtilletosum was the dominating vegetation type, but also species belonging to Eu-Piceetum dryopteridetosum were found.The main aim of the investigation was to examine natural regeneration, both under a shelterwood of 225 Norway spruce trees per hectare and on a 50 m wide clear-cut area. 2/2 bare-root spruce seedlings were planted under shelterwood and on the clear-cut area. Spot scarification was carried out here and in an adjacent stand.The seed fall was registered continuously by seed traps, and all seeds were X-ray analysed. Seeds with embryos were classified as filled and seeds without embryos as empty. Spot scarification was carried out manually within a 50 x 80 cm frame in the second and fifth growing seasons after the regeneration cutting.The humus layer including the ground vegetation was removed without disturbing the mineral soil beneath and turned upside down. The dynamics of seedling establishment were examined by marking the seedlings with plastic sticks of different colours each year. Thus it was possible to estimate the number as well as the height of seedlings of different ages during the research period.To estimate the annual diameter increment of shelter trees and trees in an adjacent stand, two bore cores were taken from each sample tree just before the final cutting. The height development of the same trees was estimated by measuring the top shoots of each year after the cutting. By use of volume functions the volume of each single tree was calculated, and the volume increment was determined as the difference between volumes in different years.Four seed years (1964, 67, 69 and 73) contributed to the natural regeneration, but seed production was modest in three of these. Although the seed supply was abundant in 1973, years with minimal or no production of germinable seeds dominated (Fig. 3). Even though the seed supply during the investigation period was relatively modest new seedlings were found in scarified spots after every seed year.However, the seedling mortality was high (Figs. 4 and 5). The best results were obtained under shelterwood, but even there only 50% of the spots had one or more seedlings 3 years after the removal of shelter trees (Fig. 7). The seedlings grew slowly below shelterwood. Thus, the oldest seedlings, which germinated in the third grow season after the cutting, attained a height of only 17 cm during 11 years (Fig. 8).On the clear-cut area the height growth was considerably better. On the other hand, both the number of seedlings and the percentage of scarified spots with seedlings were lower. In intact vegetation only a sparse element of advance growth was found, both under shelterwood and on clear-cut area. In both cases the total number of seedlings increased modestly until the shelter trees and the surrounding spruce stand were cut. However, 9 years after the final cut it was found that the number of seedlings had increased greatly on the initially clear-cut area, but only to a small extent where the shelterwood was removed (Table 9).The zero-square percentages (the number of 2 x 2 m squares without seedlings as percentage of all squares surveyed) were 41 and 59 respectively, which indicated a future volume production about 90% and 75% of normal (Braathe 1953). Probably, the main explanation of the lower number of seedlings on the initially shelterwood plot was that the greater part of seedlings germinating after the excellent seed year of 1973 died after the release cutting.On the clear-cut area the advance growth attained a height of about 3 m during 22 years (Fig. 10). At the same time the plantation was about 3.5 m high (Fig. 11). The time saved by planting correspond to about 2 years. A dense shelterwood of spruce considerably reduces the height growth of seedlings. However, the advance growth, which had been suppressed for 13 years, reacted quickly with increased growth after the release.At the end of the investigation period the difference in height between the plantation on the clearcut area and the released advance growth corresponded to about 7 years of growth. The loss of time with natural regeneration may be rather high, especially if the main part of the seeds are spread late in the regeneration period.On the clear-cut area, new seedlings were only about 50 cm high 22 years after the cutting. Probably most of these had germinated in 1974. The plantation attained a corresponding height after 6 years. After planting, both under shelterwood and on clear-cut areas, the seedling mortality was rather low.The shelterwood greatly reduced the height growth of seedlings. After 13 years, when the shelter trees were removed, the mean height was about 95 cm, versus 170 cm without shelter. After release, the seedlings reacted quickly with increased growth. The time lost by planting under shelter corresponded to about 5 years. The diameter increment of the shelter trees increased quickly and culminated in sixth year after the shelterwood cutting. During the remaining 7 years of the shelterwood phase the diameter increment remained high (Fig. 13).The shelterwood cutting did not seem to affect the height growth of the trees. The height growth of both the shelter trees and the trees in the adjacent stand decreased in the investigation period (Fig. 15). The annual volume increment during the shelterwood phase (1963-75) was 3.38 m3 per hectare, and increment of single trees was much higher in the shelterwood than in the adjacent stand (Fig. 16).The shelter trees were divided into three groups according to the diameter at breast height before the shelterwood cutting. Both the volume increment and the cone production were highest in the group of trees with the largest diameter. In cases where the shelter trees react positively to the cutting, on fields which are easy to regenerate naturally, the shelterwood method is interesting. The main drawbacks of the method are the increased danger of windthrow and a high seedling mortality associated with the release cuttings.
Forfattere
Karsten Raulund-RasmussenSammendrag
Det er ikke registrert sammendrag
Forfattere
J. Bille-Hansen M. HovmandSammendrag
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Forfattere
Bjørn LangerudSammendrag
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Forfattere
Alf Bakke Torfinn Sæther Øystein AustaråSammendrag
Pheromone dispensers containing methylbutenol, (-)cis-verbenol and ipsdienol, which are the three components of the Ips typographus pheromone, retained their effectiveness for 8 years when stored in sealed aluminium bags in an unheated room in the cellar of a storehouse.
Forfattere
Leiv M. MortensenSammendrag
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Sammendrag
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Forfattere
S. RoerSammendrag
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Sammendrag
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Forfattere
G.M. Filip Erik Christiansen C.A. ParksSammendrag
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