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.
1994
Forfattere
Hans Fredrik Hoen Knut VeistenSammendrag
The city of Oslo is surrounded by large forest areas, the socalled Oslomarka, which are intensively used for recreational purposes. During the autumn of 1992 and 1993 surveys were done among the users of Oslomarka to collect information about the reasons for visiting a particular area, the main purpose of the visit to the forest, the attitude on how the forest is influenced by the management practices, and the willingness to pay for increased restrictions on the management practices. A main hypothesis to be tested was if there were any differences in responses among users of private forests, which were judged more intensively managed for timber production, and users of municipal forests which have been managed with explicit multiple-use objectives during the last twenty years. Minor differences in responses among users of private forests and users of municipal forests were found. Only the attitude toward a statement saying that passability is not much affected by twigs and branches from forest operations could support a hypothesis that the users of private forests are more discontent (see Table 4). A smaller share of respondents in private forest agreed to this statement compared with the respondents in municipal forests, and a larger share disagreed. In both subsamples relatively more respondents agreed with positive statements about landscape attributes caused by forest management and disagreed with negative statements. Yet, 60% of the respondents gave at least one answer to the 7 or 9 statements indicating a negative view toward one aspect of the current management practices. The majority of the users gave reasons for visiting the forest which are not unique for forest areas, like calm and relaxation, be together with friends/family and exercise (see Table 2). Easiest access was the reason most of the users gave for visiting the specific area (see Table 3). This reason varied significantly with answers indicating a welfare reduction if the area where the interview took place was assumed to be reallocated from forestry and closed for recreational purposes (see Table 5). Yet, it was not given a clear definition of the size of the area connected to this question. Mean willingness to pay (WTP) for more cautious management practices in the Oslomarka, through an environmental tax on wood-products, was estimated to NOK 286 per household per year in 1992 (open-ended question) and NOK 235 in 1993 (conditional mean of a dichotomous choice). The only sosioeconomic variables varying significantly with WTP in both surveys were age (-), and expressing a negative view about the landscape in the area on at least 3 of 7/9 statements (). The regression analysis performed on the WTP-data indicated a stronger theoretical validity for responses in the 1992-sample than the 1993-sample, since WTP in 1992 varied significantly and positively with gross household income.
Sammendrag
Det er ikke registrert sammendrag
Forfattere
Karl Hilding ThunesSammendrag
Fruktlegemer av Piptoporus betulinus (Bull. ex Fr.) Karst. og Fomes fomentarius (L. ex Fr.) Kickx ble innsamlet i perioden mars til desember 1991 fra fem forskjellige skoger på Vestlandet. Billefaunaen er beskrevet i detalj. Flere faktorer bidrar i nedbrytningen av fruktlegemet og faunaen forandres betydelig i løpet av denne prosessen. Vertsspesifisitet hos de obligat levende kjukebillene er sannsynligvis også bestemt av andre faktorer en kjuken selv, fordi faunaen forandrer seg med skogtype og bonitet. Videre, den nesten vikarierende fordeling av Cis alter og C. jacquemarti kan best forklares med interspesifikk konkurranse. Det presenteres en enkel fenologi for Cis bidentatus, C. alter, C. lineatocribratus, C. jacquemarti, Leptusa pulchella, L. fumida og L. ruficollis.
Forfattere
Tron EidSammendrag
Information about the number of trees per ha in stands in development class III-V is useful for several reasons; for yield forecasts on forest level with economic calculations, for planning of thinning regimes and for cost calculations with respect to logging.The aim of this work has primarily been to map variations within stands for the number of trees per ha in order to predict how many sample plots to be distributed in a stand with certain requirements for standard error. Different sample plot sizes have been considered in this context. Several questions have also been discussed in order to settle inventory instructions for sampling number of trees per ha in practical forest management planning.The data materials have been collected from 230 stands with 4836 sample plots. The number of trees has been sampled on 100 m2, 200 m2, 300 m2 and 400 m2 sample plots, with the majority on 200 m2 plots (Table 1). The time consumption, when the sampling of the number of trees is carried out by an inventory crew of one person, has been studied for 17 stands.Table 2 shows that the mean standard deviation and the mean coefficient of variation between plots within stands are 256 trees/ha and 39.5% for 200 m2 sample plots. There are quite large differences between sites. In general the standard deviation increases and the coefficient of variation decreases when the number of trees per ha increases.Regression functions have been developed in order to predict standard deviation and coefficient of variation between plots within stands for the number of trees per ha. Different stand attributes are used as independent variables, and the functions are based on 200 m2 sample plots (Table 3). R2 are generally low. It is therefore quite likely that the predicted values become too large in some cases, and too small in others. Table 4 shows how this works for the single sites included in the data material.Table 5 shows standard deviations and coefficients of variation for stands where the number of trees is recorded with different plot sizes in the same stand, and with identical plot centers.Table 6 shows additions and deductions when the standard deviation and the coefficient of variation for other plot sizes than 200 m2 are predicted. These figures have to be used together with the regression function in Table 3. It should be emphasized that the additions and deductions are based on data from relatively few stands.Table 7 shows the mean time consumption per plot for measurements on different plot sizes. Table 8 shows the estimated number of sample plots to be distributed in a stand according to different requirements for standard error.Fig. 1 shows the estimated time consumption per stand according to different requirements for standard error. In development class III the estimated time consumption is lowest with 100 m2 plots, while the differences between the plot sizes in development class IV-V are very small.Fig. 2 shows how a regression function (S2) might be used to predict the standard deviation between plots within stands for number of trees per ha. Fig. 2 also shows how many plots which have to be distributed in a stand according to different requirements for standard errors. Sampling number of trees in practical planning is discussed in chapter 3.3.In a relascope survey it is recommended to sample the number of trees directly instead of indirectly by means of the tariff number. A direct method generally provides for the most accurate results. A direct sampling of number of trees also provides for lower time consumption than indirect sampling, if the requirements for accuracy are the same.In a relascope survey the most efficient strategy is to distribute the same number of sample plots in each stand both for sampling the number of trees and for sampling the basal area. Sample plot sizes of 100 m2 in development class III and 200 m2 in development class IV-V usually provide for a satisfactory accuracy.It is recommended to use 200 m2 sample plots in development class III and 400 m2 sample plots in development class IV-V if the requirements for accuracy are high. Also if the estimation of volume in each stand is carried out by means of aerial photographs, a direct sampling of number of trees through field work will be the most accurate method. A direct sampling in the field, however, will be more expensive than a sampling by means of interpretation on aerial photographs.A more precise comparison of these two methods, both with respect to accuracy and time consumption, should be carried out. If a systematic sample plot survey for large areas is carried out, a direct sampling of number of trees in each stand might be carried out if the economical part of the prognosis is important.
Forfattere
Øystein Dale J. StammSammendrag
The goal of the project was to collect technical data for selective harvesting operations. The main emphasis was on areas which had not earlier been studied, and in which there were a lack in knowledge. Gross operational statistics from 6 harvesters and 3 forwarders were collected throughout a period of 50 working days. This material is used as a reference representing ordinary harvesting operations. A model study of a forest estate in the Gardermoen area practicing selective harvesting was made. The main goal of the study was to see how much longer it took to administrate the selective harvesting compared to the reference material. A comparison between the motor-manual and the mechanized working methods was also made. Studies of gross operational statistics at Gardermoen showed that the portion of total working time used for planning increased from 2 % to 10 % for harvesters in the reference material and selective harvesting operations, respectively. The equivalent numbers for forwarders was 2 % and 4 %. The main reasons for the differences between harvesters and forwarders is that operational planning is normally done by the harvester operator. The differences in the portion of time required for planning were small between mechanized and motor-manual working methods in single-tree selection and small clear-cuts (1-2 daa). On the other hand, harvesters used 6 times the proportion of time for planning of group selection ( 1 daa) than that of motor-manual cutters. From the reference material and the sampled gross operational statistics from the Gardermoen study, we have worked out a system for estimating time consumption for moving forestry machines. A practical consequence of selective harvesting may be the division of harvested volume into smaller operational units and, therefore, more frequent moves between operational units.Moving forestry equipment by means of car transport: Y = 0.85 (X/32.5) Y = Time consumption in hours X = Moving distance in kilometres Moving forestry equipment by itselves along roads: Y = 0.41 (X/10.6) Y = Time consumption in hours X = Moving distance in kilometres In the Sessvollmoen area a study of harvester production in a pine shelterwood was made. The production of a two-grip harvester for cutting in a pine shelterwood can be described with the following function: Y= 14.819 8948 * (X*X) 0.356 * T Y = Production in m3 ob. per effective hour (E0) X = Average tree size (m3 ob.) T = Number of trees harvested per daa The production for mechanized cutting of windthrown trees will be reduced by 60-70 % compared with ordinary clear-cutting. Knowledge from other experiments shows that the frequency of wind thrown trees can be a considerable problem in shelterwoods. In the Rakkestad area we saw how the production of a forwarder varied with different levels of volume removal. The time consumption for forwarding in selection harvesting can be described as Y = ((0.0124*Rb0.0131*Lb0.017*Rt0.021*Lt)/Lv) 2.72 - 0.0166 * Ut Y = minutes per m3ob (E0) Rb = Return distance on base or strip road (m) Lb = Driving distance on the base or strip road while loaded (m) Rt = Return distance in the terrain (m) Lt = Driving distance in the terrain while loaded (m) Lv = Volume per load (m3 ob.) Ut = Volume removal in m3/daa (ob.)
Forfattere
Frode Fjærtoft Aasmund BunkholtSammendrag
Denne rapporten omhandler to skurforsøk med bjørk hvor det ble benyttet to ulike tømmersorteringsreglementer og to ulike trelastsorteringsreglementer. I det ene skurforsøket ble det skåret 59 stokker med samlet volum 16,3 m3 u.b., mens man ved det andre skurforsøket skar 443 stokker med samlet volum 101,7 m3 u.b. Tømmeret ble samlet inn tilfeldig innenfor de gitte rammene for tømmersorteringsreglementene. Sortimentsfordelingen bør derfor være representativ for hva man kan forvente ved en kommersiell utnyttelse av bjørk. Tømmerreglementet som ble benyttet ved skurforsøk II var bl.a. strengere med hensyn til krok enn tømmerreglementet benyttet ved skurforsøk I. For det strengeste reglementet viste Chi-kvadrat-testen signifikant forskjell i sorteringsutfallet av trelast mellom de ulike tømmersortimentene. Dette var ikke tilfellet ved bruk av det andre reglementsettet, som bl.a. omfatter tømmerreglementet som i dag benyttes ved eksport av finérbjørk til Finland. Trelasten ble ikke nedklasset på grunnlag av tørkeskader (vridning og sprekk), da slike skader sjelden kan relateres til tømmerkvaliteten, men i hovedsak skyldes tørketekniske forhold. Skurforsøkene viste imidlertid at det er viktig å foreta lengdesortering av trelasten før tørking. Møbel- og trevareindustrien krever en tørrhetsgrad ned mot 10%. Trolig vil det være mulig å utvikle reglementer for tømmersortering og trelastsortering som stemmer bedre overens med hverandre enn de reglementsettene som er benyttet under disse to skurforsøkene, men reglementene benyttet under skurforsøk II må sies å være et skritt i riktig retning av hvordan reglementene bør utformes.
Forfattere
Øystein Dale Hans E. AamodtSammendrag
Kjøreskader ved terrengtransport av tømmer er uønsket både ut fra generelle miljøhensyn og for skogproduksjonen. Markskader er spesielt problematiske ved lukkete hogster med mye kjøring inne i bestand, da disse i liten grad lar seg reparere uten å skade trærnes røtter. Tiltak for å begrense markskader ved ugunstige forhold (bæresvak og bløt mark) er derfor av stor interesse. For å kvantifisere effekten av barlegging ble det høsten 1993 gjennomført forsøk med kvistdekking av kjøreveier. Kvistene ble lagt ut systematisk med henholdsvis 10 og 20 kvister pr. meter. Forsøket ble gjennomført på sandjord på to felter (god og dårlig bæreevne) klassifisert utfra vanninnholdet i jorda. Forsøket ble utført med en stor firehjulsdrevet landbrukstraktor (Valmet 755). På feltet med god bæreevne oppnådde en ingen effekt av barlegging på spordybdeutviklingen. Densitetsøkning ble redusert med 30 - 50 prosent i forhold til udekket etter 36 kjøringer. Effekten var likevel liten, da kontrollstrekningen (uten kvister) bare hadde en densitetsøkning på 7,7 prosent ved 20 cm måledybde. På feltet med dårlig bæreevne førte barlegging til reduksjon både i spordybde og i jordpakking, men det kunne ikke påvises noen forskjell mellom kjørestrekningene med 10 og 20 kvister pr. meter. Hjulspordybden ble redusert med inntil 75 prosent ved barlegging og en fikk samtidig en redusert densitetsøkning på inntil 54 prosent. Kontrollstrekningen (uten kvister) fikk en densitetsøkning på 20 prosent ved 20 cm måledybde.
Sammendrag
Det er ikke registrert sammendrag
Forfattere
Toril Drabløs Eldhuset Olav Teigen Kristian BjorSammendrag
Det er ikke registrert sammendrag
1993
Forfattere
Anita JensenSammendrag
Registrering av jordstatus skjer regelmessig på de intensive skogovervåkingsflatene i regi av Overvåkingsprogram for skogskader. Flatene er geografisk spredt over hele landet. Her beskrives endringer i jordas faste fase på flatene fra etableringen i 1986 til ny prøvetaking i 1991. For alle flatene sett under ett, var det få endringer i de jordbunnskjemiske egenskapene i løpet av de fem årene. De få observerte endringene finner vi hovedsakelig på de sørligste flatene, og de kan i første rekke tilskrives prosedyrer ved prøvetaking i felt. De registrerte endringer i jordas faste fase er ikke av en slik størrelse at de kan fanges opp etter fem år. Eventuelle endringer må være store nok til at de overskygger naturlige variasjoner i jorda. Det kan slås fast at fem år er en for kort tid til at dette har skjedd.