Terrestrial plants, mainly trees, account for 80% of the Earth’s total biomass, 450 billion tons of dry carbon and more than two trillion tons of “live weight.” So the idea of planting new forests to sequester CO2 from the atmosphere has long seemed logical.
Musk, you’re wrong!
Many, from scientists to Ilon Musk, have called for and are still calling for the planting of trees to combat global warming. The authors of a new paper, which was published in Global Change Biology, decided to look into whether everything with this is as obvious as it seems at first glance.
They analyzed a number of predecessor papers. One of them, published in 2025, showed that mature European beech forests between 1984 and 2022 simultaneously experienced rapid growth of green biomass and massive loss of soil carbon from depths of 50 to 90 centimeters. The loss of soil carbon amounted to 17% of its capture by growing trees.
That is, the mature forest, even under conditions of vigorous growth, gave less carbon capture than expected.
What exactly accelerated the loss of soil carbon so much is still unclear. Presumably, it is the matter of a two degree rise in temperatures in these forests over the same period and an increase in precipitation of 100-200 mm per year. The higher the temperature and humidity, the more active soil microorganisms decompose dead biological material in the soil, returning its components to biogeochemical turnover.
Scientists also cited another mechanism: the more precipitation (and warming leads to an increase in global precipitation), the less need for trees to put down deep roots capable of collecting water from lower soil horizons. Old roots of dead trees gradually decompose at depth, and new roots do not replace them, which further reduces biomass in soils.
Pine trees have enhanced the effect
The situation with beech forests may still be relatively light. Other work last year showed that soils under mature pine forests contained half as much carbon as the same soils under grass vegetation next to those forests. This carbon loss offset one-third of the carbon dioxide uptake of the pine forest studied.
In addition, the carbon in the soil under the forests appeared to be bound in less stable forms than under other vegetation types. This creates considerable uncertainty for the future. It turns out that we do not know how and when all this carbon from the soil may be lost by it to the atmosphere.
The authors of the study explained in a media commentary that “we can’t rely too much on forests to mitigate the effects of climate change, we can’t, because there is too much we don’t yet understand. Despite the growth in tree biomass, we may be losing ‘carbon capital’ – the carbon that is stored in soils over the long term.”
