Finland Continues to Become Swampy with Accelerated Bog Growth

Within the swamps, which make up roughly a third of Finland’s land area, there is still room for expansion. It was once thought that they would have already spread to all areas susceptible to swamp formation, implying that their growth would have ceased or at least decelerated.

However, researchers acquainted with the bog borders, namely Teemu Juselius-Rajamäki, Minna Väliranta, and Atte Korhola, argue otherwise. They state that the expansion of bogs has only sped up in recent centuries.

In their study, they measured the growth rate of five separate bog areas in Northern, Southern, Western, and Eastern Finland using radiocarbon dating.

The areas studied represented the northern plains, which are wettest in the center, the more prevalent uplands in the south, which are wettest at the edges, and their transition zone.

The rate of bog growth, which began after the ice age, was fastest approximately 3,500 years ago, then it decreased. However, around 1,500 years ago, a new surge in growth began, which continues to the present day.

The examined bogs are currently growing at an average rate of about one centimeter per year, according to the Global Change Biology report.

While this rate may seem slow, it is significant due to the sheer size of the swamps.

The researchers believe that the average growth rate could increase if more swamps are studied.

The base of the bogs currently under study rises steeply towards the edges, which is the main factor slowing their growth. In milder climates, sphagnum moss can spread several meters per year.

Bog growth is encouraged by rainfall and by terrain that retains water in the soil.

Raised bogs facilitate their own growth by draining rainwater from their high centers towards their lower edges. Wildfires also aid the spread of marsh plants over other vegetation.

With current climate change predicted to increase both rainfall and wildfires in Finland, bogs are expected to continue expanding. Juselius-Rajamäki speculates that in the long run, the growth of bogs will help mitigate global warming.

While the carbon reserves in bogs act as a long-term brake on their expansion, their growth can also contribute to warming. This is because more methane, a potent greenhouse gas, can be released from the damp edges of expanding bogs.

Published in Science in Nature 1/2024

Correction updated on February 2 at 4:15 p.m.: A link to the study in the scientific journal Global Change Biology was added. On February 4 at 8:30 p.m., a sentence stating that bogs absorb or sequester as much carbon as forest plants and soils combined was removed from the title and text. Instead, peat in natural bogs serves more as a carbon reserve.