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1995
Forfattere
Erik NæssetSammendrag
In Norway, about 5500 km2 are surveyed annually for forest management planning. Approximately 50 % of that area is recorded by aerial photo interpretation. In order to carry out economical planning by means of data collected by photo interpretation, the logging costs have to be computed. The logging costs can be determined utilizing cost functions (Anon. 1994). The number of trees per cubic meter of a stand is an important input variable of such functions. The first objective of the present study was to develop models for determination of number of trees per cubic meter, cutting cost, skidding cost, and total logging costs of mature forest stands of Norway spruce and Scots pine by means of photo interpretation. The second objective was to investigate the accuracy of practical use of these models. A material of 119 tallied stands of Norway spruce, Scots pine, and various mixtures of spruce and pine was applied in this study. The stands were distributed on four different sites in southeastern Norway. The cutting cost, skidding cost, and total logging costs were computed from the field measurements by means of the cost functions (Anon. 1994) (Table 1). Five photo interpreters measured and interpreted the stand mean height, the crown closure, and the tree species distribution of the individual stands by means of panchromatic photographs at the approximate scale 1:15000 and a stereo plotter of the second order (Wild B8). The site quality was determined from the site quality layer of the official Economic Map Series. First, the accuracy of the determination of number of trees per cubic meter from aerial photographs was investigated. The model for computation of number of trees per cubic meter is displayed in Fig. 1. Mean differences between photo estimated and field measured number of trees per cubic meter in the range -4.7 % to -43.1 % were found (Table 2). The standard deviations for the differences between photo estimates and field measurements varied between 14.9 % and 37.6 %. The large systematic deviations were partly due to calibration problems related to the interpretation of crown closure. The logging costs were determined according to three different models. In model I (Fig. 2), the logging costs are computed directly from the tariff number and the number of trees per cubic meter of the individual stands. In model II (Fig. 3), a stratified systematic sample plot inventory is used to correct the systematic errors of tariff number and number of trees per cubic meter. The corrected values of the individual stands are used for determination of the costs. In model III (Fig. 4), a stratified systematic sample plot inventory is used to correct the systematic errors of tariff number and stand volume, while the number of trees of the individual stands is recorded by field measurements. The number of trees per cubic meter is computed by means of the corrected stand volume and the number of trees. The corrected values of the individual stands are used for determination of the costs. For model I a mean difference between photo estimated and field measured logging costs of maximum 13.0 % was found (Tables 3, 6, and 9). For model II and model III the maximum mean differences were 4.8 % (Tables 4, 7, and 10) and 5.9 % (Tables 5, 8, and I 1), respectively. For practical use of model II and model III a somewhat larger systematic error than indicated by the present results should be expected. The standard deviations for the differences between photo estimated and field measured total logging costs were 4.6-13.0 % (Tables 9, 10, and 11). Model II and model III seem to yield systematic and random errors of a similar magnitude as field based relascope surveys that not record the number of trees, but basal area, stand mean height, and tariff number only.
Sammendrag
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Forfattere
Thomas J. Savage Rodney CroteauSammendrag
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Sammendrag
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Foredrag – Blue-stain fungi associated with the spruce beetle Dendroctonus rufipennis
Halvor Solheim
Forfattere
Halvor SolheimSammendrag
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Sammendrag
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Forfattere
G. GoffengSammendrag
Lukket
Forfattere
Ketil HaarstadSammendrag
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Forfattere
G Guttormsen B. R Singh Alhaji S. JengSammendrag
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Forfattere
Alhaji S. Jeng B. R SinghSammendrag
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