Publikasjoner

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1993

Sammendrag

Forsøksområdet ligger omkring 1070 meter over havet i Vestre Gausdal, Oppland fylke og er på 8500 dekar. Arealene ligger over bjørkeskoggrensen. På behandlete deler dominerte dvergbjørk i busksjiktet, stedvis med innslag av einer og vier. Feltsjiktet var dominert av blåbær og smyle, med innslag av fjellkrekling og tyttebær. Bunnsjiktet besto av moser, vesentlig husmoser, og av forskjellige lavarter. Både reinlavarter og islandslav med lignende arter var representert. Tilsammen ble det brent 350 dekar, både i praktisk skala og i små ruter. Nedkapping av busksjikt, delvis med gjødsling, ble bare gjort på små ruter. Både nedkapping og brenning førte til en sterk reduksjon i utbredelsen av blåbærplanter. Stadige frostskader og konkurrerende vegetasjon (smyle) førte til at denne reduksjonen fortsatte gjennom flere år.Krekling tålte rydding, men overlevde ikke brenning. Mengden av insekter var sterkt redusert på brent mark etter 4 til 5 år sammenlignet med intakt vegetasjon i nærheten. Dette er de tre viktigste næringsemnene for rype i yngleperioden. Resultatene stemmer stort sett overens med tidligere undersøkelser. Det var ingen effekt på fordelingen av territorielle rypestegger av brenningen. Selvom materialet har et begrenset omfang, må det likevel kunne konkluderes med at ingen av de tiltak som er undersøkt var egnet til å forbedre rypebiotoper under de forholdene som er beskrevet.

Sammendrag

4 site quality classification methods have been tested in young forest stands; height-age-, intercept-, vegetation- and subjective site quality classification. Two functions are applied for intercept site quality classification. One function where the site quality is based on the intercept (5 years height increment above 2.5 meter off the ground) and the tree species (intercept). And one function where also different characteristics of the growing place are included (extended intercept). Also for site quality classification by means of vegetation two different functions are applied; one which is based on vegetation type and on other characteristics of the growing place (vegetation), and one which in addition use the breast height age to explain the site quality (vegetation with age) (see also Appendix 1). The registrations are carried out on systematically distributed sample plots in 45 stands. The data are described in Table 1, 2 and 3. Table 4 shows that intercept gives significantly higher site quality than extended intercept. The mean difference for all plots is 0.5 meter. It has not been possible to point out any obvious reasons for this difference. Table 5 shows that vegetation with age gives significantly higher site quality than vegetation. The mean difference for all plots is 3.5 meter. The introduction of age as an independent variable has clearly made the site quality higher. Table 6 shows that 100 m2 sample plots give significantly higher site quality than 10 m2 sample plots both for height age and for intercept. The mean differences for all plots are 1.0 meter and 0.7 meter for the two methods. 100 m2 sample plots is recommended in practical inventories. Table 7 shows generally small differences between height-age and intercept. For the best site qualities, however, height-age gives the highest values, while intercept gives highest values for the poorest site qualities. A test, where plots with young trees (T1.3 15 years) have been excluded, does not change the relative relations between the two methods. For both methods there is a certain possibility for an overestimation of the site quality if the soil depth is tiny. Table 7 also shows that vegetation with age gives a significantly higher site quality than height-age for 2 out of 3 sites, and both for spruce and pine. The mean difference for all plots is 1.2 meter. The introduction of age as an independent variable has made the site quality higher. It might be questioned whether it has made the site quality too high. It is not possible based on the present data material, however, to give any appropriate answer to this question. Table 7 further shows that subjective site quality classification gives significantly lower values than height-age, intercept and vegetation with age. Several possible reasons for the differences are pointed out. It is also quite likely to perform person-dependent systematic errors when subjective classification methods are applied. The results of this study basically point out two possible correct site quality levels in young forest stands. One possibility is that the methods height-age, intercept and vegetation with age all give an approximately correct level. The other possibility is that vegetation (without age) and subjective site quality classification give an approximately correct level. According to the discussion it is quite possible that the correct level is somewhat lower than the level indicated by height-age, vegetation with age and intercept. It is, however, less likely that the level is as low as vegetation (without age) and subjective site quality classification are indicating. Subjective site quality classification has so fare been recommended for young forest stands. This method has also been applied for practical inventories. We know that person-dependent systematic errors are usual when subjective classification methods are applied. Because of this, and based on the results of this study, it is quite likely that site quality classification in young forest stands will be done more accurate if some of the three other methods were applied.