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KLIMAFORSK-Stort program klima

The impact of increasing spruce plantation area on the carbon balance of forests in Western Norway

Alternative title: Virkninger av økt granplanting på karbonbalansen i skog på Vestlandet

Awarded: NOK 10.0 mill.

Project Number:

255307

Application Type:

Project Period:

2016 - 2023

Funding received from:

Partner countries:

Tree planting and tree species change have been suggested as a government policy to mitigate climate change in Norway with the aim to increase the annual CO2 uptake as well as the long-term storage of carbon (C) in forests. The strategy includes replacing native broadleaf species with fast-growing species like Norway spruce to rapidly produce biomass and sequester C. The BalanC project aimed at providing more complete C budgets based on field studies in paired stands of native, naturally generated birch and planted Norway spruce at four locations in Western Norway. The work comprised 1) quantification of C stocks and C stock changes in tree biomass, ground vegetation biomass and soil, climatic feedback related to albedo and C budgets related to the wood product chain including use of wood products to substitute more carbon-intensive products, as well as 2) in-depth studies of soil C processes and changes in microflora/fauna and understory vegetation species groups. Results from the paired stands showed a significant increase in the tree biomass C stock in spruce compared to birch stands, whereas the understory vegetation C stock was higher under birch compared to spruce. There were no changes in dead wood C stocks or in the total soil C stock down to 30 cm soil depth. We found a significant C accumulation in spruce biomass relative to birch 45-60 years after the tree species change. When including the carbon debt incurred from the removed birch, the net C capture varied from 49 to 97 ton C ha-1 at three locations, whereas the 45-year stand at Stranda showed a net C loss of 69 ton C ha-1. The net C capture was partly related to stand age. Based on data from comparable NFI stands, model estimates with prolonged rotation period showed a substantial increase in the climate mitigation potential at the target years 2050 and 2100. In comparison, clear-cut followed by spruce planting resulted in a substantial climate warming impact in 2050 and 2021 compared to prolonged rotation used as a reference. The effect was mainly related to differences in standing tree biomass, combined with decomposition of harvest residues and potential loss of C from soil. Whereas changes in albedo had a climate warming impact following the tree species change, the change in albedo following clear-cut resulted in a positive climate impact both in 2050 and 2100. The effect of albedo was, however, low compared to the accumulation and loss of C from biomass with prolonged rotation and harvesting. Including the use of wood products based on the ratio of saw wood and pulp wood of spruce in Western Norway still suggested a considerable climate warming impact following harvest. The final climate effect related to substitution seems to be determined by the choice of product. A large variation was found in the theoretical substitution effect for selected pairs of woody and non-woody products with the same function, where cross laminated beam substituting steel beam had the highest substitution effect amongst four selected alternatives. The climate effect was mainly related to avoided emission from non-woody products. Transport of timber was found to be the single most important factor that affected the C emissions between planting and delivery of timber at the production gate. The tree species change was found to affect the stability and vulnerability of long-term C storage in the soil. We found a negative correlation between C stocks in mineral soil and living tree biomass in the spruce stands, as well as a significant increase in the C stock of the humus layer of spruce, possibly linked to an increase in fungal biomass. Due to differences in stabilizing mechanisms in humus and mineral soil, the increased C stock in the humus layer under spruce is expected to be less stable with climate change and disturbances. Changes in the composition and stability of the soil organic matter were evaluated based on lab incubation, photoacoustic spectroscopy and thermal analyses of samples from the humus layer and mineral soil. The effect of the tree species change seemed to reflect qualitative rather than quantitative changes in the soil C stocks. For understory vegetation species groups, the mean cover of herbs, ferns, and graminoids as well as ligneous plants were lower under spruce. In upper soil layers of spruce, base saturation, exchangeable Mg, and % N decreased, and exchangeable acidity increased relative to birch. Changes in understory species diversity and soil chemistry affected the composition of the microbial communities, especially for fungi, and the soil bacterial and fungal richness diminished in the spruce stands. The tree species change also impacted the eukaryome for both taxonomic and functional categories that are involved in food-web control in forest soil. Future decisions on tree species change and management of existing stands need to consider long-term C storage and biodiversity, as well as risk factors related to climate change.

Prosjektet samlet forskere fra fagområdene jordfag, skogbruk, skogøkologi, mikrobiell økologi, klimavitenskap og industriell økologi fra ulike institusjoner nasjonal og internasjonalt, og har derigjennom bidratt til økt tverrfaglige samarbeid og kunnskap. Prosjektets fokus har strukket seg fra mikrobielle samfunn via jordprosesser, jordkjemi og bunnvegetasjonsgrupper til kvantifisering av C-lagre og C-akkumuleringen i skogøkosystemet på bestandsnivå, effekt av albedo, og livssyklusanalyser av tømmer brukt for å erstatte mer karbonintensive produkter. Resultater er formidlet gjennom prosjektperioden i form av omfattende foredragsvirksomhet, med skogforvaltningen og skognæringen som de viktigste målgruppene, samt gjennom presentasjoner på internasjonale konferanser og publisering i internasjonale fagfellevurderte tidsskrift. Prosjektet har ellers utviklet metode for termisk analyse i jord, samt forbedret modellestimater for albedo på Vestlandet. Potensielle effekter av prosjektet er knyttet til både tiltak for å redusere de globale klimaendringene, og effekter av skogtiltak på biologisk mangfold: I følge IPPC kreves presserende handling for å begrense den globale oppvarmingen til 1,5°C. For å stabilisere den globale temperaturen må netto utslipp av CO2 reduseres til null. Skog er regnet som å være klimanøytral ved slutten av en rotasjonsperiode. I lys av IPCC sine referanseår for å begrense globale klimagassutslipp (2030, 2050, og 2100), er det også viktig å evaluere endringer i opptak og utslipp fra skog for disse referanseårene. På Vestlandet er hogst av plantet gran vanlig ved bestandsaldre 45- 60 år. Prosjektets resultater antyder at en forlenget rotasjonsperiode kan medføre i en betydelig klimagevinst, mens hogst av plantet gran etter treslagsskifte kan til sammenlikning medføre betydelige CO2 utslipp både i 2050 og 2100. Resultatene kan bidra i vurderinger av skjøtselstiltak og økonomisk kompensasjon ved klimaskogbruk for å redusere utslipp av CO2 knyttet til hogst. Prosjektets resultater er også aktuelt for spørsmålet om hvorvidt avvirkning av plantede granbestander på Vestlandet kan gi økte risiko for ulike former for skred. Resultater fra prosjektet kan eller bidra til økt bevissthet rundt bruk av klimavennlige treprodukter og substitusjon, og illustrerer et behov for virkemidler som sikrer at tilgang på ‘mer’ treprodukter fører til at disse blir brukt istedenfor, ikke i tillegg til, bruk av eksisterende karbonintensive produkter. Prosjektets resultater har fått økt aktualitet etter ratifiseringen av FN’s Naturavtale om naturmangfold og biodiversitet i 2022. Prosjektet har bidratt til ny kunnskap om mikrobielle samfunn og artsrikdom i skogøkosystem på Vestlandet, samt effekter av treslagsskifte på endringer i mikrobielle samfunn, artsgrupper av bunnvegetasjon og jordkjemi, og sammenhenger mellom disse. Potensielt kan kunnskapen inngå i videre evaluering av endret valg av treslag ved treslagsskifte og planting på Vestlandet.

To mitigate climate change in Norway, tree species change has been proposed as a government policy to increase the annual uptake of CO2 and long-term storage of carbon (C) in forests. This strategy relies mainly on the potential of fast-growing species like Norway spruce to rapidly produce biomass and sequester C as opposed to native, deciduous species like birch. However, crucial parts of the overall C-sequestration potential of forestation have been ignored due to the lack of available information and assessment complexity, resulting in an incomplete picture of the C balance of this measure. These parts include soil C, albedo, and emission connected to wood-product life-cycles, all expected to change considerably with tree species. Forests in western Norway host some of the largest soil C pools in Scandinavia, and are roughly estimated to store more than 3 times the C stock found in biomass. Moreover, compared to boreal forests of the cooler and flatter regions of eastern Norway, little is known empirically surrounding the albedo dynamics in coastal forest ecosystems of western Norway. A major goal of the tree species change policy is to promote the transition to a bioeconomy by the enhanced use of tree biomass for bioenergy, materials, etc.; however, the fate of C in the wood-product chain has not been accounted for along with the rest of the C-pools and flows in contrasting forest ecosystems. The BalanC project aims at providing a complete C budget of the effect of tree species change that comprises static (C stocks in biomass and soils) and dynamic parts (C-processes, albedo and wood product chain) of C in the C-rich forests of western Norway where large tree species changes are planned. By investigating these multiple dimensions and their responses to tree species change, we intend to provide the knowledge base required for a complete and solid assessment of the overall effect of the proposed policy on C-sequestration and climate change mitigation in Norway.

Publications from Cristin

Funding scheme:

KLIMAFORSK-Stort program klima