Effect of afforestation on the organic carbon stock of soils

Since 1922, the territorial proportion of forests has increased from 12% to 22% due to large-scale afforestation in Hungary. These planted forests bind huge amounts of carbon dioxide from the atmosphere. The sequestered carbon is partly stored in the above-ground biomass of forests in the form of organic matter. At the same time, a similar amount of carbon can be found underground. The research aims to assess the effect of afforestation on the amount of organic carbon stored in the soil (SOC).

During our investigations, we collected samples from 3 study areas from the Hungarian Great Plain. We compared the soil of the poplar and acacia forests in the sample areas with the grassland soils located directly next to these plantations. By the natural conditions, the pH of forest (7.75 and 8.29 pH(H₂O)) and grassland (8.01 and 8.45 pH(H₂O)) samples was weakly alkaline/alkaline. We measured a lower pH value in case of forests, which clearly shows the leaching effect in the forest soils. The average humus content of the tested soil samples was 0.94%. The lowest measured value was 0.09%, while the highest was 4.21% which clearly showed that dry sandy soils have a low organic matter content.

The soil and the litter cover contain 7 to 37 tons SOC/ha. The differences between the studied areas were very large. The carbon stock of the soils was higher in forest stands in every case. This shows that in long term the afforestation increases the amount of carbon stored in soils compared to grasslands.

This article was made in frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.