Why did Finland's forests change from a carbon sink to a permanent source of emissions in a few years? The reason is simple: emissions from the soil increased exponentially. But what caused this explosion? There are at least three reasons for this, which I will explain in the thread below. 1/9 - ThreadSky

ilkkaleinonen.bsky.social • 16 days ago

Why did Finland's forests change from a carbon sink to a permanent source of emissions in a few years? The reason is simple: emissions from the soil increased exponentially.

But what caused this explosion? There are at least three reasons for this, which I will explain in the thread below.
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adamkristensson.bsky.social•16 days ago

Thanks. Very interesting. Reason 2: but I also heard that there is an increased harvest rate in Finland, meaning Reason 2 is halted, since we get less aging trees with increased harvest rates?

ilkkaleinonen.bsky.social•16 days ago

The harvest rate increased until the peak year 2018. After that, the harvests have decreased and the tree carbon sink has increased. So the the increase of emissions during the recent years is really about soils. Yes, the harvest rates are quite high, but the average age of trees still increases.

adamkristensson.bsky.social•16 days ago

Ah. Thank you very much for the explanation.

ilkkaleinonen.bsky.social•16 days ago

Reason 1: In Finland, trees have been a carbon sink since the 1970s. The sink was created by forest regeneration and the development of forest management practices.

When the growth of the forest accelerated, the production of litter (e.g. dead leaves, needles, fine roots) also increased.
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ilkkaleinonen.bsky.social•16 days ago

The litter accumulated in the soil, which meant that the soil was also a carbon sink for decades.

But litter is not a permanent carbon storage. The more litter accumulates in the soil, the more carbon it releases into the atmosphere when it decomposes.
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ilkkaleinonen.bsky.social•16 days ago

And eventually, the rate of decomposition was higher than the rate of formation of new litter. The soil became a source of emissions.
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ilkkaleinonen.bsky.social•16 days ago

Reason 2: At the same time as the decomposition of litter accelerated, litter input into the soil also decreased. The crown of aging trees is smaller in relation to the trunk volume, so less litter is produced now.
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ilkkaleinonen.bsky.social•16 days ago

So, aging reduces the sink in two ways: through slower growth of living biomass and through reduced litter production. Therefore, the carbon input to the forest carbon storage is now continuously decreasing as trees are not getting any younger.
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ilkkaleinonen.bsky.social•16 days ago

Reason 3: Perhaps the most important reason for the increase in emissions, however, is the acceleration of decomposition activity due to rising temperatures. This is especially the case in the soils of drained peatlands, where there are huge amounts of dead organic matter ready to decompose.
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