Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
1991
Forfattere
Erik ChristiansenSammendrag
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Forfattere
Tore FrognerSammendrag
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Tore SkrøppaSammendrag
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Tor J. JohansenSammendrag
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Forfattere
Tron EidSammendrag
This work deals with some consequences erroneous data basis might have for the planning and the management of forest holdings. The way in which the data basis, which is divided into the inventory basis, the model basis and assumptions, influences the planning process, is showed in Fig. 1. The considerations are mainly concentrated on the inventory basis, and the variables site quality, stand age, basal area and mean height. Sensitivity analysis is carried out for 10 model forests (Table 1), where consequences for plan suggestions, decisions and accomplishment of decisions are considered. Examples of how erroneous measurements might influence the property value of a forest are also given. Incorrect site quality changes both the increment and the treatments. This means that the total production of a forest might change considerably. If the site quality is one class too high or low in all stands, the production levels of the forests change by 30-40%. The largest deviations are found when the site quality is overestimated, and in the pine forests (Table 3). Incorrect site quality also influences the relative age of a stand. Fig. 2 shows how the economically mature areas, and the corresponding volumes, change due to incorrect site quality. Examples where the share of economically mature areas and volumes decrease from 50%, when the site quality is overestimated by one class, to near zero when the site quality is underestimated by one class, are not unlikely. Such deviations do, of course, also influence the balance quantity and the fellings according to economical cutting maturity (Table 4). Especially the changed rotation ages might lead to large deviations. Incorrect site quality might also insert a silvicultural program which is too intensive or extensive according to correct site quality, and the interest rate. In such cases the net present value decreases (Table 5). Also the property value is influenced by an incorrect site quality. In the model forests these values change 15-20% if the site quality is over- or underestimated by one class (Table 6). An incorrect stand age influences the forecasts due to changed increment, and due to changed time for final fellings. The changes of the increment, as a result of an overestimated or an underestimated stand age, generally decrease the balance quantity in the first case, and increase it in the second case (Table 7). In forests where the share of old stands is low, the conclusion might be the opposite, i.e. the balance quantity increase when the age is overestimated, and decreases when the age is underestimated. This is due to a changed share of mature stands. The balance quantities change by 6-8%, and the fellings according to economical maturity change about 10%, if the basal area has a bias of 10% (Table 8). The net revenues change in the same way because the mean tree, and accordingly also the prices and costs/m3, remain the same, in spite of incorrect basal area. To accomplish felling suggestions based on incorrect data, e.g. 10% too large basal area, influence the possibilities of the future. There might, for example, be too few mature stands to accomplish the suggested balance quantity strategy in the future (Fig. 3). The fellings have to be reduced some years later. This is in conflict with the decision-makers goal. Also an incorrect basal area changes the property values of the forests. 10% incorrect basal area makes them change by 7-9% (Table 9). 10% too large mean height makes the balance quantities change by 6-9% in the spruce forests, while they change by 3-5% in the Scots pine forests (Fig. 4). The deviations for the net revenues are larger because the mean tree, and accordingly the prices and costs/m3, are changed. This is particularly the case in the pine forests where the net revenues change by 12-15%. Some examples of how errors in the model basis, and how incorrect assumptions might influence the balance quantity, are also given. The balance quantities increase by 4-6% if the diameter increment is overestimated by 10%, while the balance quantities increase by 3-6% if the lower limit of the rotation ages are assumed to be 10 years too low (Fig. 5). Combinations of different errors might either strengthen or hide effects. An overestimated site quality, basal area and diameter increment at the same time will, for example in forest no. 1, lead to an overestimation of the balance quantity by 19%, while there is a very small change if the site quality is overestimated and the diameter increment is underestimated at the same time (Table 10).Taking into account the relatively moderate systematic errors assumed in the examples, that combinations of errors might appear, and that also errors in functions or errors connected to the assumptions for the treatments are quite likely, the errors appearing in practical applications are probably larger than those considered in this study.
Forfattere
Severin WoxholttSammendrag
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Mette Goul ThomsenSammendrag
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