The soil CO2 emission at the three most common forest habitat types in Poland

The soil CO₂ emission is one of the most important parts of forest carbon balance, and accurate estimation of this flux is fundamental for appropriate forest management aimed at adaptation and mitigation of climate change. The soil carbon dioxide flux density is determined by different factors, e.g. soil temperature, humidity, and C-content. The Polish forest habitats classification (based on the climate and soil conditions) provides the practical basis for the effective extrapolation of local carbon dioxide emission observations to larger areas. Thus, the main goal of this study was the estimation of the annual dynamics of the soil CO₂ emission at three of the most common forest habitats and to select the most reliable model that can be commonly applied to managed forests. There were three experimental sites selected for this study, and they represented the following forest habitats: optimal conditions for pine forest (OP), rich conditions for pine forest (RP) optimal conditions for mixed oak and pine forest (OOP). These three habitats represent 66% of forested areas in Poland. The sites were located in Oborniki Forest Inspectorate in the Greater Poland Voivodship, Western Poland. The CO2 emission was measured by means of the manual dynamic opaque chamber attached to the infrared gas analyzer (LI-840 LI-COR, USA). There were 3 collars (25 cm diameter) inserted about 15 cm depth into the ground at each site, and the measurement campaigns were carried out from 16^th of March 2022 8^th of March 2023, at 3-week intervals. The soil measurement system (TMS-4, TOMST, Czechia) was applied for discrete (15-minute interval) measurements of the air and soil temperature and soil water content at each collar. Additionally, soil analysis was made at each site. The initial analysis of obtained results shows that the model based on both soil temperature and soil water content can be considered the most accurate and reliable. The richest forest habitat (OOP) with the highest soil C-content is characterized by the highest annual soil CO₂ emission.