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.
1995
Forfattere
Tron EidSammendrag
Non-productive forest land is defined by a potential yield capacity of less than 1.0 m3/ha/year inclusive bark. The portion of non-productive forest areas in stands are usually recorded subjectively in practical inventories. The aim of this work has been to develop sampling methods which, as fare as possible, are based on objectivity. The problems related to non-productive forest areas are restricted to sites with occurrences of rock on surface, shallow soils and obvious productive areas within stands. Non-productivity in wetland areas and mountain areas was not considered. Three different methods for estimation of the portion of non-productive areas were investigated. Method 1 was based on an assumption of a link between actual and expected number of trees per ha, and the portion of non-productive area in stands, i.e. missing trees were assumed to be a result of non-productivity. Method 2 was based on classification on sample plots in a systematic grid within stands. Variables related to soil depth and vegetation types were used for classification on each plot. Method 3 was based on a prediction of site quality on sample plots systematically distributed within stands. Plots where the site quality was predicted to be less than H40=5.0 meter, i.e. a potential yield capacity of less than 1.0 m3/ha/year inclusive bark, were classified as non-productive. Site quality was predicted by means of regression functions developed for the purpose of classification. Site properties as soil depth, soil type and vegetation type were used as independent variables. 72 blocks located in Southeast Norway were selected for the investigation. The blocks were subjectively located in stands with occurrences of rock on surface, shallow soils and productive areas within stands. Longitude, latitude, height above sea level, slope and conditions with respect to water penetration and soil type were recorded for each block. All blocks were covered by a systematic grid of points (1x2 meter). Soil depth and vegetation type were recorded for each point. Height, diameter and coordinates were recorded for all trees on each block. In addition the age was recorded for trees suitable for site quality classification. Based on the experiences from the field work, and on the considerations around different sources of errors, a systematic sample plot inventory within stands, with classifications on each plot (Method 2), is recommended. The sample plot size should be small, e.g. circles with radius 1 meter. The following recommendations are given for classifications on each plot;The sample plot should always be classified as non-productive if the portion of rock on surface is larger than 50%.The sample plot should as a rule be classified as non-productive if the mean soil depth is less than 10 cm. If mean soil depth on the plot is 7-10 cm, the following considerations should be performed; - Vaccinio-Pinetum boreale, Eu-Piceetum myrtilletosum or a richer vegetation type on the plot indicate productivity, - trees within a plot which are a natural part of the stand with respect to size and species indicate productivity, - small areas within a plot with large soil depth (larger than 30 cm) indicate productivity. If mean soil depth on the plot is 10-15 cm, the following considerations should be performed; - Barbilophozio-Pinetum lapponicae or Cladonio-Pinetum boreale on the plot indicate non-productivity. Pure subjective judgments of the portion of non-productive forest land in stands should also in the future be the main element in practical inventories. As early as at the stand delineation phase, however, one should try to eliminate those areas which obviously are non-productive. In this way the amount areas with subjective judgments are reduced. Estimation of the portion of non-productive areas by means of systematic plot inventories within stands should be used from time to time to calibrate the subjective judgments. This is particularly important in sites with occurrences of rock on surface and shallow soils within stands. The results of such sample plot inventories might also be useful as reference data when non-productive forest land is estimated by means of photo interpretation.
Forfattere
Øystein DaleSammendrag
Rapporten bygger på innsamling av data for markskader fra fem regioner i Norge. Materialet omfatter data fra 117 hogstflater og 69 basveier. Det er gjort registreringer på tilsammen 487 prøveflater på hogstfeltene og 299 målestrekninger på basveiene. Formålet med undersøkelsen var å kartlegge omfanget av markskader etter tømmerdrifter, og å finne årsaker til skadene for å kunne komme med anbefalinger for å redusere disse. Driftsdata for tømmerdriftene og klimadata fra nærmeste målestasjon er i analysen blitt koblet sammen for å se på hvilken betydning været kan ha for omfanget av markskader.Skadene var gjennomgående minst etter de driftene som var gjennomført med lett utstyr (landbrukstraktor). Forskjellen er større enn forventet ut ifra tidligere undersøkelser. Årsaken er trolig at disse relativt små maskinene ikke kan brukes under de dårligste forholdene.Gjennomsnittlig spordybde på basveien for drifter i vinterhalvåret (middeldøgntemperatur under null) var 10,3 cm. I sommerhalvåret økte sporskadene med ca 73% til 17,8 cm i gjennomsnitt. Økt avvirkningsaktivitet i sommerhalvåret vil derfor kunne øke sporskadene i skogbruket betraktelig, dersom det ikke systematisk iverksettes tiltak for å unngå markskader. Dersom sporskader med gjennomsnittlig dybde over 25-30 cm skal repareres vil dette utgjøre henholdsvis 13% og 8% av basveienes lengde i gjennomsnitt ved vinterdrifter. I sommerhalvåret vil dette øke til 27% og 22%, dersom det ikke gjennomføres tiltak for å begrense skadene. Store årlige variasjoner i værforhold gjør det vanskelig å detaljplanlegge med hensyn på riktig tidspunkt for skogsdriften. Derfor vil det i tillegg til god planlegging være viktig å ha rutiner for å begrense sporskader (barlegging, valg av kjøretrasé osv.) og for hvordan de skal repareres. Sporskadene er hovedsakelig et transportproblem ved tradisjonelt flateskogbruk. For selektive hogster vil problemet også omfatte selve hogsten. Sporskader/råteproblematikken vil legge sterke begrensninger på bruken av denne typen hogster i sommerhalvåret spesielt i granskog på bæresvak mark. Registreringer av markskader på hogstflatene viste at bare 1,7% av totalarealet hadde skader med dybde over 5 cm.
Forfattere
Arne Olav Stuanes O. Janne Kjønaas Helga van MiegroetSammendrag
Nitrogen has been added to a forested 0.52 ha headwater catchment at Gårdsjön on the southwest coast of Sweden to study the ecosystem response to elevated nitrogen deposition. The catchment is dominated by naturally generated, mixed-age conifers, mainly Norway spruce, with Scots pine in dry areas. After a pre-treatment period of about 1 year, nitrogen was added to the whole catchment as ammonium nitrate by means of sprinklers at an intensity of 3 mm h-1 (average concentration 230 mmol N1-1). Total nitrogen input as throughfall to the catchment increased from the ambient 12.5 kg N ha-1 year-1 in the pre-treatment year to a total of 47.3 kg N ha-1 year-1 in the treatment years. Soil solutions were collected using tension lysimeters at four locations covering a moisture gradient from the dry upper to the wet lower parts of the watershed. Results from these locations were compared with soil solution composition at two locations in a nearby control catchment. After 2 years of nitrogen addition, the volume-weighted average nitrate concentrations in the treated catchment were higher than the pretreatment values, especially in the upper soil. Concentrations showed a progressive increase over time. The lack of the same increasing trend in the control catchment precludes natural variations in climatic conditions as the main cause for this increase. Relative to inputs, nitrate concentrations in soil solution were low and showed large variations between the drier and wetter locations. Differences in nitrate concentrations between pre-treatment and treatment periods declined with soil depth, indicating that most of the added nitrogen was consumed in the upper soil. The results from soil solution do not indicate increased nitrogen leaching below the rooting zone in the treated catchment and thus based on these results alone there is as yet no indication of nitrogen saturation.
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
Interessa for naturleg forynging av furu er aukande på Vestlandet. For å betra spire- og veksetilhøva er det ofte ein føremon å blottleggja mineraljorda. Forsøk med markberedning med lette gravemaskinar og landbrukstraktor, har vore gjennomført i fire felt i Voss kommune. Landbrukstraktoren (51 kW) var utstyrt med eit markberedningsaggregat laga for flekkopptaking i ei rad. Dei tre beltegravemaskinane (8-9 tonn) var alle utstyrde med 80-90 cm brei skuffe. Traktor og gravemaskin vart køyrde ved sida av kvarandre i kvart felt for å samanlikne produktivitet og arbeidskvalitet. Førarane hadde som mål å laga minimum 250 flekker pr. dekar, med ein flekkstorleik på omlag 0,5 m2 blottlagt mineraljord. Produktiviteten, målt i markbereidd areal pr. virketime, vart høgast ved bruk av gravemaskin. Landbrukstraktoren fekk seinka produktivitet når terrenget vart bratt. I stigning over 20 prosent markbereidde traktoren berre i nedoverbakke. Gravemaskinen synte ingen produktivitetsreduksjon i bratt terreng. Båe maskintypane fekk færrast flekker i feltet med den vanskelegaste terrengoverflata. Flekkstorleik og blottleggingsprosent (mineraljord) vart noko større med gravemaskin enn med landbrukstraktor, unnateke på det feltet som var lettast å køyra. Generelt syntest gravemaskinane å vera minst påverka av vanskeleg terreng. Gravemaskinar greier seg med færre køyredrag enn traktorar og kan derfor unngå ein del terrenghindringar som ein landbrukstraktor ikkje klarer. Førarane i desse forsøka var røynde med maskinane sine, men hadde ikkje markbereidd før. For landbrukstraktoren er det nytta ein noko høgare produktivitet i sluttanalysene enn det resultatet som vart oppnådd i feltforsøka. For landbrukstraktor vil dessutan feltstorleik og -form ha innverknad på køyre- og snutid og dermed produktiviteten. Gravemaskin har høgare markberedningskostnad enn landbrukstraktor. Båe maskintypar får høg dekarkostnad på små areal, fordi ein får mykje flyttetid i høve til arbeidstid på flatene. Redusert framkomstevne og lågare kvalitet på arbeidet i ujamnt terreng, set grenser for bruk av landbrukstraktoraggregat til markberedning på Vestlandet. Etter erfaringane i dette forsøket, er mindre beltegravemaskinar (8-9 tonn) godt eigna til markberedning. Gravemaskin kan forutan til markberedning og nyttast til grøfting, sporreparasjon og vegvedlikehald.
Forfattere
Erik NæssetSammendrag
In Norway, about 5500 km2 are surveyed annually for forest management planning. Approximately 50 % of that area is recorded by means of aerial photo interpretation. A method for determination of gross value for individual forest stands by means of aerial photo interpretation has previously been developed (Nsset 1990, 1991a). The logging costs can be calculated by means of cost functions (Anon. 1994) utilizing stand characteristics related to the trees and characteristics related to the terrain, such as slope and skidding distance. Some properties related to the terrain can be derived from digital elevation models (DEM). The objective of the present work was to develop an integrated method for determination of gross value and logging costs for individual mature forest stands by means of aerial photo interpretation, DEMs, and geographical information systems (GIS). Computation of gross value as well as logging costs were based on the so-called mean tree of a stand, i.e. a tree defined by mean diameter by basal area and Loreys mean height. The models for computation of gross value and logging costs are shown in Fig. 1 and Fig. 2, respectively. In addition to stand characteristics related to the trees, Fig. 2 shows that slope and skidding distance must be derived in order to compute the logging costs. The method for computation of gross value and logging costs was demonstrated by means of a case study from a forest area in Froland municipality, South Norway, of about 710 ha. Black-and-white aerial photographs at an approximate scale of 1:15000 and a stereoplotter of the second order (Wild B8) were used to delineate the stands, measure stand mean height, and interpret crown closure, site quality, and tree species distribution of the individual stands. For all the mature stands within the area, information on topography and ground conditions interpreted in the aerial photos were used to suggest skid paths for timber transportation from the stands via existing skid roads to landings along the forest roads or public roads.The stand boundaries, the suggested skid paths, existing skid roads, existing forest roads and public roads, and contour lines taken from the official Economic Map Series at the scale 1:5000 with 5 m contour interval were digitized into separate map layers applying the pcARC/INFO software. All the forest stand characteristics were related to the stand map layer.The stand characteristics required for the gross value computation were exported to the SAS package (Anon. 1985), which was used for calculation of gross value as well as logging costs. The data flow is shown in Fig. 4. The gross value was calculated according to the model displayed in Fig. 1. The average slope and skidding distance of the individual stands were required for the logging costs calculation. The grid based GIS package IDRISI (Eastman 1992) was used for determination of slope and distance (Fig. 4) before the logging costs could be computed by means of the model shown in Fig. 2. A DEM was generated with IDRISI from the digitized contour lines (Fig. 5).The slope was computed (Fig. 6), and average slope of the individual stands was found and exported to the SAS package via pcARC/INFO (Fig. 4). The skidding distance for a stand was defined as the average distance on the terrain from the individual grid cells of a stand via the digitized skid paths and skid roads to landings along the forest roads or public roads.The crossings between the skid paths/roads and the forest/public roads were used for landing points. However, IDRISI provides procedures for calculation of ground plane distances only. A method for computation of approximate on terrain distances was therefore developed. The average extension of distance due to slope for traversing a grid cell was found (Eq. 3). A grid map where the grid cells were assigned the values of the average extensions due to slope was generated. A stand boundary layer where the stand boundaries were assigned the value -1 was produced. The average extension layer was overlaid the stand boundaries and the various path and road maps (Fig. 7 and Fig. 8), such that all stand boundary cells, except the crossings between the boundaries and the roads, attained the value -1. All other cells, including the crossing cells, attained the average extension values. The resulting layer (Fig. 10) was used as friction layer and the forest/public road layer was used as source layer to indicate the cells from which skidding distances should be determined utilizing the COST procedure (COSTGROW algorithm) of IDRISI. The cells of the friction layer assigned the value -1 (the stand boundary cells) served as absolute transportation barriers. The computed skidding distances (Fig. 11) were, however, based on an on the terrain straight line distance within the individual stands (Fig. 3). The computed distance for each grid cell was therefore multiplied by an average ground plane winding factor of 1.16 found for 28 of the stands within the study area (Table 1). Finally, the average corrected skidding distance for each stand was derived and exported to pcARC/INFO and SAS for logging costs computation. Computed gross value, logging costs, and gross profit are displayed in Figs. 12, 13, and 14, respectively. The suggested method for computation of gross value of mature stands is likely to give satisfying accuracy.Assuming that some of the calculations of the logging costs model (Hkl and n, Fig. 2) be corrected by means of sample plot inventories, a random error (standard deviation) of about 10 % should be expected. At present, practical large scale application of the presented method is hindered by a lack of proper digital elevation data. Implementation of the method requires also integrated computer programs on more powerful computer platforms than the one used here.
Forfattere
Ketil KohmannSammendrag
Denne undersøkelsen er foretatt for å gi svar på et stadig tilbakevendende spørsmål: Hvilken plantetype er skogbruket best tjent med. Med dagens dyrkingsteknikk kan pluggplanter lages på en rekke ulike måter,- med ulike dyrkingsformer, pottebrett, og med ulik intensitet i dyrkingen, bruk av veksthus i hele eller deler av dyrkingsperioden, styrt indusering av veksthvile på høsten m.m. En type pottebrett gir derfor nødvendigvis ikke en helt klart definert plantetype. Undersøkelsen består av tre ulike serier av forsøk. Den første serien består av syv felt med plantetyper som avviker en del fra ordinære plantepartier med hensyn på høyde og alder. Av denne serien trekkes den konklusjon at granplantene ikke må være for små ved utplanting. Hovedårsaken til avgang i denne serien er snutebillegnag og beiting av sau. Den andre og tredje serien består av elleve felt i tre fylker. Her kommer frem at den ettårige pluggplanten med hele dyrkingstiden i veksthus har lavest overlevelse. Mellom de øvrige plantetyper, toårig M95, 2/2 barrot og toårig M60 er det ikke sikre forskjeller. Mens barrotplantene har høyest overlevelse på feltene i Telemark, er det de to-årige pluggplantene (M95 og M60) som overlever best i Vestfold og Buskerud. I alle forsøk er de toårige M60-plantene høyest ved forsøkets slutt.
Forfattere
Erik Trømborg Birger SolbergSammendrag
This report describes the model used in the project Modelling the Norwegian Forest Sector. The purpose of this project is to do consistent analyzes of how different changes in factors affecting the business environment of forestry and forest industries in Norway will effect the forest sector. The model used is developed by professor Markku Kallio at Helsinki School of Economics. The model is based on the same main principles as the model developed at the International Institute for Applied System Analysis in the 80s, IIASAs Global Trade Model, GTM. The model is named the Norwegian Trade Model, NTM. NTM is a regional partial equilibrium model with linear constraints (like production capacity limits and upper bounds on harvesting), and a non-linear object function (through non-linear timber supply functions). The model maximizes net social pay-off for all products and regions. Net social pay-off is calculated as the area under all demand functions, minus the sum of transportation costs resulting from trade with other regions, and minus productions costs in the forest industry including timber costs given by non-linear supply curves. This describes according to economic theory, a situation under perfect competition where all consumers and producers maximize their surplus. The model consists of four main parts: A model for timber supply, including the connection between harvesting level and timber costs, and between todays harvesting and future timber production and harvesting. A model for the forest industry that describes how timber is transformed to intermediate- and endproducts and how central factors such as capacity, locations and production costs change over time. A model for product demand that relates demand for forest products to factors such as price, volume, economic growth and exchange rates. A model for trade between regions that relates a fixed location of timber resources and forest industry to demand and supply of forest products. The model consists of 10 domestic regions and two regions for respectively export and import. 27 products are included in the model of which there are six roundwood assortments, 5 pulp grades, 2 board grades, 3 sawnwood products and 9 different paper and board products in addition to recycled paper and energy wood. The dynamics of the model is created through recursive programming where the equilibrium problem for the analyzing period is split into a number of equilibrium solutions, one for each time step. The equilibrium for the first time step t, gives together with changes in timber supply, production capacity, costs and demand, basis for the equilibrium solution in next time step t1. The model describes 5 time steps of 5 years each from year 1990 to year 2010, where the model estimates product prices, harvesting, production on plant and regional level and trade between regions in each time step. A model will always be a strong simplification of the real world. It is therefore important that results from the model are evaluated on the basis of assumptions within the model and the uncertainty of data used. It is our opinion that NTM is a appropriate model for analyzes of the Norwegian Forest Sector. Compared with other models we feel that NTM has the following advantages:The regional aspects is very well taken care of.The forest sector is well described as the forest sector is included at individual plant level. The optimization algorithms secure economic consistency in each scenario alternative. The non-linear timber supply equations used gives most likely a more realistic descriptions of the forest owners behaviour than linear supply equations.The algorithm applied is highly efficient, making possible solutions in short time. Every model has shortcomings towards the real world and it is important that the results from the model are evaluated in relation to these shortcomings. In NTM is it our opinion that the following factors are burdened with highest uncertainty:The linearization of the demand functions might give too large changes in demand when price change.The substitution between different timber assortments on both the supply and demand side is just described to a limited extent in the model.The model is not very user friendly.There will in general be significant uncertainty linked to the huge amount of data demanded by the model. The main purpose with the model is to quantify relative changes connected to certain assumptions and to clarify mechanisms. This purpose has to be emphasized when both results and model are evaluated. Used in this way, it is our opinion that NTM can give valuable insight in many aspects of the forest sector.
Forfattere
Ane Gram Dæhlen Øystein Johnsen Ketil KohmannSammendrag
Tretti provenienser av gran fra størstedelen av granas utbredelsesområde i Norge samt 15 ulike frøpartier fra Lyngdal, Kaupanger og Opsahl granfrøplantasjer ble dyrket og deretter frysetestet under indusert herding i klimakammer. Målet var å påvise variasjon i høstfrostherdighet, sammenlikne planter fra frøpartier sanket i skogen (provenienser) med planter fra plantasjefrø av samme provenienser, og å sammenlikne planter fra frø produsert i et varmt (1989) og et kaldt frøår (1987) i Lyngdal frøplantasje. Variasjonen i frostherdighet fulgte en jevn utvikling hvor herdigheten økte fra sør mot nord. Hele 87 % av variasjonen kunne forklares med proveniensenes breddegrad og høyde over havet. Planter fra Lyngdal frøplantasje (bruksområde: Trøndelag og Nordland) var mer skadet enn planter fra bestandsfrø fra tilsvarende breddegrader og høydelag. Lyngdalfrø fra 1987 ga herdigere planter enn frø fra 1989. Samsfrø fra Kaupanger (til bruk i høyereliggende områder på Østlandet) produserte mindre herdige planter enn tilsvarende høydelagsprovenienser, men forskjellen var ikke så stor som tidligere rapportert. Vekstkraftige avkom fra testede mødre i Kaupanger ble betydelig mer skadet. De tilsvarte provenienser fra 200-400 m o.h. Planter fra Opsahl hadde bedre herdighet enn de fleste av proveniensene fra tiltenkt bruksområde (500-700 meter, 59-62°N). Vekstrytme og herdigheten til granavkom kan påvirkes av værforhold det året hvor frøet produseres (foreldremiljøet gir ettereffekter på avkom). Den svakere herdigheten til avkom fra Lyngdal og Kaupanger og forskjellen mellom 87- og 89-årgangen fra Lyngdal skyldes et annet klima i frøplantasjene sammenliknet med foreldrenes opphavssted (endringer i daglengde og temperatur under blomstring) og sannsynligvis forskjellene mellom det kalde (1987) og det varme (1989) frøåret i Lyngdal.Fordi tidligere undersøkelser tyder på at ettereffektene er varige opp til 10 år, kan bruken av frø fra Lyngdal tilsvare en proveniensforflytning 1 - 2 breddegrader sørfra, og bruken av Kaupangerfrø kan tilsvare en forflytning 200 - 400 meter oppover på samme breddegrad.Inntil vi får mer informasjon fra feltforsøk, anbefaler vi at planter fra Lyngdal og Kaupanger fortrinnsvis brukes i de mildere strøk innenfor de opprinnelige tiltenkte bruksområdene i henholdsvis lavlandet og i kystområder i Trøndelag og Nordland og i lier med god kaldluftsdrenering i høyereliggende strøk på Østlandet.
Forfattere
Birger Eikenes Bohumil Kucera Frode Fjærtoft O.N. Storheim Geir Isak VestølSammendrag
The project Quality of wood with selection cutting and shelterwood cutting is one of the projects in the research program Forest ecology and multiple use. The purpose has been to analyse wood quality in uneven-aged forests. The material originates from seven experimental plots with selection forests. Of these plots two are located in Nordland, three in Nord-Trndelag, one in Oppland, and one in stfold. Five mature trees were harvested from each plot. The sample trees should be big enough to give sawnwood of the dimension 50x200 mm from the butt log, 50x150 mm from the second log (the middle log), and 50x100 mm from the third log (the top log). The project is divided into three parts:Detailed analyses of annual growth ring width and density were done on trunk discs from different tree heights.Mechanical, technological, and physical properties were measured on small, clear specimens together with anatomical characteristics.Timber in standard structural sizes was sorted both visually and mechanically before testing for modulus of elasticity and static bending strength in the laboratory. At stump height (1 % of tree height) mean annual growth ring width increases from 0.7 mm near the pith to 2.6 mm near the bark. The rate of increase in annual growth ring width is strongest near the pith, and declines towards the bark. Basic density is showing the opposite development, and declines from ca 450 kg/m3 near the pith to ca 350 kg/m3 near the bark. In 20, 40, 60 and 80 % of tree height it was found very small variations in density from the pith towards the bark. Mean basic density for the different experimental plots varies from 350 kg/m3 to 379 kg/m3. Mean for the whole material is 365 kg/m3. The corresponding figures for annual growth ring width show variation in mean values for the plots from 1.38 mm to 2.01 mm, with a mean for the whole material of 1.64 mm. For small, clear specimens the following mean values were found: Modulus of elasticity in static bending 13.4 GPa, static bending strength 79.9 MPa, compression parallel to grain 39.7 MPa, impact bending strength 35.9 kJ/m2, and static hardness in radial direction 2281 N, in tangential direction 2014 N, and in longitudinal direction 2741 N. Standard structural timber was sorted visually and in two different types of stress grading machines. Mean modulus of elasticity is calculated to 11.4 GPa, and mean static bending strength to 42.0 MPa. Results from the present material show that selection forests dont have the same development in annual growth ring width and density as spruce planted on high site index in Eastern and Western Norway. At stump height the annual growth rings near the pith are very narrow, and the growth rings are getting wider towards the bark. Basic density shows the opposite development. Near the pith basic density is high, and it declines towards the bark.Of the experimental plots at our disposal six plots of a total of seven were localized far north or at high altitudes, and therefore the plots are less representative for the main productive spruce forest areas in Norway. Besides, the site index is considerably lower for the present material from selection forests than the materials used for comparison (G11-17 against G23-26). Still we can conclude that wood quality from these experimental plots of selection forests show more uniform annual growth ring width and density, both in stem cross section and in tree height than wood from planted forests. It is not possible to separate juvenile wood on the basis of density and annual growth ring width in wood from selection cutting. Even if the stem form is not specially good, the analyses show that it is possible to get very good wood quality, particularly regarding strength properties, in selection forests which are near the timber line of the natural growth area for spruce in Norway.