Rune Eriksen

Chief Engineer

(+47) 480 57 250
rune.eriksen@nibio.no

Place
Ås H8

Visiting address
Høgskoleveien 8, 1433 Ås

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Abstract

The re-measurement of permanent forest inventories offers a unique opportunity to assess the occurrence and impact of forest disturbances. The present study aims at exploring the main forest damages in Norway based on the extensive data of several consecutive national forest inventories during the period 1995–2014. Five of the most common disturbance agents in Norway are selected for analysis: wind, snow, browsing, fungus and insect damage. The analyses focuses on the frequency and variation along time, the average damage at stand level and the spatial patterns of damage occurrence, resulting in a characterization of the damage produced by disturbances in Norway. The highest damage occurrences by disturbance agent are due to browsing, snow and wind. Snow presents a decreasing temporally trend in damage frequency in the studied period. By forest type, mature and intermediate birch forest are found to be more affected by snow damage, whereas mature spruce forest is by wind damage. The results from this study provide support to the hypothesis that damages by autumnal moth (Epirrita autumnata) on birch are more common in mature stands. No major attacks from bark beetle (Ips typographus) are found, probably related to the lack of major storm damages in the period. Forest types susceptibility to fungus has no apparent variation over time except in the last years, as increased occurrence is observed on mature spruce stands probably correlated with warmer than average periods. Browsing damage causes the most severe losses, as expected, in young stands, and is allocated mainly on the most productive forests. Although some of the disturbances present locally moderate effects, the results show no major disturbances threatening Norwegian forests in the studied period. Finally, the Norwegian national forest inventory demonstrates its reliability as a basis to understand the occurrence and effects of major natural disturbances.

Abstract

Miljødirektoratet utarbeidet i 2014 et kunnskapsgrunnlag for hvordan vi kan omstille Norge til et lavutslippssamfunn (Miljødirektoratet 2014). I rapporten ble en rekke tiltak i skog beskrevet. Denne rapporten er en del av neste fase av dette arbeidet, som er å utdype analysen av mulige tiltak og virkemidler. Her beskriver vi, på oppdrag fra Miljødirektoratet, et utvalg klimatiltak i skog. Det er på ingen måte noen uttømmende oversikt over klimatiltak, men dekker et utvalg som det var ønske om å belyse nærmere. Disse er belyst nærmere med hovedvekt på karbonopptak og –lagring. Betydning for andre økosystemtjenester, som for eksempel biodiversitet og friluftsliv, er ikke belyst. Hovedkonklusjonene fra dette arbeidet kan kort oppsummeres slik: Fra 1990 og frem til 2012 har et bruttoareal på 1,4 mill. daa blitt avskoget (NIR 2014). Basert på data fra Landsskogtakseringen ser vi at den viktigste årsaken er nedbygging av skogareal til ulike formål (73 % av arealet), etterfulgt av omdisponering til beite (16 %). Om lag 29 % av skogen som avvirkes, hogges før hogstmodenhetsalder. Av dette arealet utgjør hogstklasse IV 25 %, mens hogstklasse III eller yngre utgjør 4 %. Skog definert som ”yngre skog” etter forslag til revidert PEFC skogstandard utgjør 9 %. Generelt benyttes relativt skånsomme metoder for markberedning i Norge i dag, og disse er vurdert til sannsynligvis å ha liten eller ingen effekt på karbonmengder i jorda over tid og over det totale areal. Tettere planting gir høyere volumproduksjon tidlig i bestandets liv. I følge resultatkontrollen i 2013 hadde 29 % av det totale foryngelsesarealet et plantetall under anbefalt nivå i bærekraftforskriften. Framskrivningene av skogbestokningen viser at en fortsettelse av dagens praksis på årlig foryngelsesareal fra 2015 og frem til 2100 akkumulert gir 83,5 millioner tonn CO2 lavere opptak enn om arealet hadde vært plantet med anbefalt tetthet. Høyere plantetetthet gir også økt mulighet for å ta ut virke gjennom tynning. Vi mener det er potensial for økt tynningsaktivitet, uten at dette vil redusere produksjon (opptak) på lenger sikt. Tynning kan øke potensialet for mer bruk av GROT (heltretynning). Ved tynning og gjødsling kan andelen sagtømmer i det hogstmodne bestandet øke, og samtidig kan tynning være ønskelig for å lage stabile bestand som kan overholdes utover normal hogstmodenhetsalder. Uttak av hogstrester (GROT) gir råstoff til bioenergi, som kan brukes til å erstatte fossile brensler. Forutsatt høstet på en bærekraftig måte, kan uttaket av GROT sannsynligvis økes uten redusert fremtidig produksjon (opptak). En lavskjerm med bjørk over granforyngelse vil, dersom den skjøttes riktig, gi en høyere total volumproduksjon på arealet over ett omløp sammenlignet med et renbestand med gran.

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Abstract

Sallow (Salix caprea L.) and rowan (Sorbus aucuparia L.) constitute small proportions of the deciduous tree volume in Scandinavia, but are highly preferred winter forage for moose and red deer, which occur at historically high densities. Thus, a possible decline of these tree species has been indicated. Against this background, we have reviewed the life histories of relevance for browsing, as well as the basic biology and genetics of sallow and rowan. The species show similarities with respect to short lifespan, small size and sympodial growth pattern, which are risk factors in a browsing context. They also have high juvenile growth rate, important for growing quickly out of reach of browsers. Sallow depends strongly on disturbance for establishment and is more demanding with respect to soil and light conditions than rowan, possibly important for the substantially lower abundance of sallow on the Norwegian Forest Inventory plots. Similarly, the relative recruitment of small size classes of sallow is less than for rowan. Although recruitment is reported to be hampered in wintering areas with high moose or red deer densities, the inventory data, however, dating only back to 1994, do not suggest a general decrease in any of the species. Sallow and rowan saplings show low mortality in moose and deer dominated areas and the species can be characterised as rather resilient to browsing. Of more concern is that browsing can constrain the development of mature rowan and sallow trees locally, with possible consequences for associated epiphytic biodiversity.

Abstract

A rapid increase in the frequency of Dutch elm disease (DED), a wilting disease of elm trees caused by bark-beetle vectored fungi, was observed in the early 1990s on several wych elm stands around Oslofjord, southern Norway. To examine the current status of the disease and its impacts on elm population, disease frequency and size distribution of elms were recorded at four locations. Northern parts of Lier, a municipality most affected by DED in Norway 15 years ago, showed in the survey season 4% disease frequency, whereas 13.8% of trees were dead, the dead trees having accumulated over several years in the unmanaged stands. In southern parts of the municipality the mean disease and death percentages were 1.9 and 2.4%. Compatible with their low disease incidence in early 1990s, the other two areas now examined, municipality of Larvik and district of Grenland, showed comparably low frequency of DED. Northern part of Lier showed significantly higher overall density of elm trees per hectare than the other examined areas, and also the small elms below 5 cm in d.b.h. were most frequent in this region. In contrast, the density of large trees was lower in northern Lier than in the other examined areas. These data suggest that regeneration of the tree is not prohibited owing to the disease but that the large trees have been locally reduced in frequency as a result of DED. The superior general density of elm trees in northern Lier, owing to the exceptionally rich soil in the warm southern slopes of the region,> may have contributed to the rapid increase of DED in the area 15 years ago and to the subsequent settlement of the disease outbreak as a chronic stage.

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Abstract

Ambitious targets for renewable energy production in Norway draw attention to biomass potent-ials. The objective of this report is to review the state of the art regarding research on estimation methods, the availability and production of tree biomass resources for energy purposes in Norway in order to indentify knowledge gaps and thus facilitate appropriate focus, development and priorities regarding research for the coming years. The review focuses on biomass from pri-mary forest production with emphasis on Norwegian conditions, but also considers international research, especially from the other Nordic countries. Three main subject areas are considered: - biomass estimation - biomass resources and availability - biomass production. The first part of this report comprises an overview of existing biomass equations and associated inventory methods applied for estimating biomass in Norway. The overview includes a description of the Norwegian National Forest Inventory data as a basis for large-scale biomass assessments. The second part of the report comprises an overview of previous Norwegian assessments of biomass as an energy supplier as well as suggestions for improvements in such assessments. Improvement possibilities regarding the impacts of environmentally oriented restrictions, appropriate models for productivity and cost calculations regarding biomass harvesting systems, and implementation of biomass-related features in existing decisions support systems to facilitate analyses, where timber production and biomass production for energy purposes are equally important, are identified. The final part of the review focuses on silvi-cultural options aiming at optimizing the value of total biomass instead of the conventional approach to silviculture where the main focus is timber values.