This is a short summary of some of the “take home messages” from a large part of the talks that were held at the Ecoforest conference in November 2023. The purpose of this summary is to make forest research more available for anyone interested in effects of forestry and climate change on carbon stocks and dynamics, biodiversity, and ecological processes. Be aware that this summary does not include everything that was presented during the conference, and it may contain small errors or mistakes.
Contributors to this summary: Vilde Lytskjold Haukenes, Milda Norkute, Rieke Lo Madsen, Lisa Fagerli Lunde and Line Nybakken.
Impact of forestry and climate change on carbon dynamics and stocks
Speakers referred to: Lars Vesterdal, Karina Clemmensen, Michael Gundale, Jogeir Stokland, Carl-Fredrik Johannesson, Karolina Jörgensen, Janne Kjønaas
About 70% of the global terrestrial C storage is in the boreal forest. This carbon storage is varying spatially. However, in Norway, up to 80% of the boreal forest carbon storage is in the soil. There is a continuous build-up of carbon in undisturbed forest soils, and the carbon in the soil can be very old, especially in the mineral soil. To maintain and facilitate build-up of carbon in the boreal forest, understanding how different forest management strategies and climate change impact carbon dynamics and stocks is crucial.
Tree species and vegetation:
- The soil organic carbon (SOC) stocks vary with tree species. There is more SOC in the forest floor under spruce when compared to ash and maple. This is due to:
- Differences in litter quality (e.g., more lignin in spruce)
- Differences in mycorrhiza, arbuscular mycorrhiza (AM) in ash and maple and ectomycorrhiza (EcM) in spruce.
- Differences in pH (lower pH in soil connected to Spruce)
- Difference in microbes
- We do not only see a build-up of SOC under spruce, but also a redistribution of carbon. The other tree species have more carbon in the mineral soil.
- Amount of carbon in the mineral soil is explained by litter quality but not by microbial or soil faunal communities.
- Labile litter may form more stable soil organic matter (SOM) over time à need for longer time frame in litterbag studies.
- Fine root decomposition: AM tree roots decompose slower than EcM roots.
- Increased mass loss of organic matter through association with decomposing EcM fungi.
- Ericaceous dwarf shrubs and their fungal root associates promote humus build-up.
Deadwood:
- 40% of carbon from deadwood is going into the SOC pool in the form of lignin, decomposed by brown-rot fungi.
- Proportion of carbon (in the form of lignin) increases with decay class in the remaining deadwood.
Harvest:
- 10% of SOC is lost quite fast after clear-cut.
- Soil carbon recovers 10-75 years after clear-cut.
- Overall, four times larger carbon flux in old growth forest when compared to managed forest.
Nitrogen fertilization:
- Not higher carbon input to the system with nitrogen fertilization. However, respiration is reduced (slower SOM decomposition) which can increase SOC.
- With lower nitrogen addition, modest carbon response per unit nitrogen. Soil carbon driven by above and belowground litter and slower decomposition.
- With fertilization, trees take up nitrogen directly and reduce uptake via mycorrhiza (reduced EcM in the forest floor).
- Cortinaruis ssp. are EcM, and they can mine SOM which contributes to a faster C-turnover and recycle their own biomass. Cortinarius ssp. which is connected to carbon loss are sensitive to nitrogen addition.
- Nitrogen-fertilization leads to a shift in the balance of decomposition pathways à more hydrolysis relative to oxidation.
Tundra/ tree line:
- A lot more SOC in the tundra, gradient from forest à forest edge à shrub-heath à heath.
- Saprotrophs in litter (decompose).
- Mycorrhiza in humus (import new carbon).
Impact of forestry and climate change on biodiversity
Speakers referred to: Jari Kouki, Mari Jönsson, Reijo Penttilä, Panu Halme, Anders Dahlberg, Markus Melin, Rune Halvorsen
In Norway 48% of red-listed species live in forest, 84% of these species is connected to old forest, and 1/3 – 1/4 is connected to deadwood. Thus, it is very important to understand how different forest management regimes, as well as climate change impact biodiversity.
Forest fire:
- Higher number of red listed species on burnt sites.
- Highest impact on biodiversity short time after fire.
Harvest:
- Less saprotrophic beetles in clear-cut.
- Large community change in beetles after harvest, both immediate and after 20 years.
- Retention forestry positive for deadwood supply in the longer run, support higher biodiversity and continuity.
- Retention forestry reduces negative effects of intensive harvest on saproxylic beetle richness.
- Heterogeneity support richness of rare species and biodiversity.
- Large dead and alive aspen are important for biodiversity.
- To leave buffer zones (>30 m) to streams promote biodiversity.
- If the trees disappear, the precondition for mycorrhiza disappear. The more trees you leave, the higher probability of maintaining a higher species richness.
- Snow damaged trees that were left in forest hosted many red-listed species, bark beetles and predator species (predators of bark beetles).
- Large diameter of deadwood is important for biodiversity.
Climate:
- Biodiversity has decreased over the past 30 years, – 30% species richness overall.
- The boreal forest floor is getting greener and poorer in species. Less vascular plants, more of the common bryophytes (e.g., Sphagnum has increased a lot).
Urban forest:
- Less clearcuttings than in production forests à So, are urban forests valuable habitats for soil microbiota?
- The more unique the tree species are the more unique the microbes are.
On the topic of near-natural forest and clear-cut forest
Most of the productive Norwegian forest has historically been severely influenced by humans. Around 1940, clear-cutting was introduced, and since then, 60-70% of the Norwegian forest has been clear-cut (referred to as cultural forest). Today, the remaining ~30% of the Norwegian forest that has never been clearcut, and was established before 1940, can be referred to as near-natural forest. This proportion of the productive forest is growing older, but it can never increase in size. Rather, 1-2% of the near natural forest is harvested each year, resulting in a loss of the near-natural Norwegian forest. As we are currently approaching a second round of clear-cut of the forest that was clear-cut in the 1940’s-1960’s, locating and protecting the near-natural forest is crucial.
Some suggested management measures to increase biodiversity and soil carbon storage:
- Conservation burning regularly.
- Leave patches of trees (retention forestry) to maintain deadwood supply.
- The more trees you leave, the better for the mycorrhiza and soil carbon storage.
- Avoid clear-cutting.
- Increase rotation length.
- Leave buffer zones around streams.
- Leave buffer zones to rocky outcrop and wet forest (best effect on lichen and bryophytes).
- Leave windthrow and snow damaged trees, this is good for biodiversity, but they also host predators of bark beetles.
- Protect the remaining near-natural forest.
Explanation of terms
Retention forestry: Leave trees. Examples: Buffer to mire, wet forest, buffer to water, buffer to rocky outcrop, coniferous tree groups, deciduous tree groups, single standing trees.
Mycorrhiza: Symbiotic relationship between root of plant and fungi. Ectomycorrhiza (EcM) use nutrient from dead organic matter, while Arbuscular mycorrhiza (AM) depend on nutrient released from saprotrophic microbes (microbes that decompose organic matter).