Impact of recent forest protection on deadwood carbon stocks

The reduction of carbon dioxide levels in the atmosphere is one of the most pressing issues in the context of global warming. Forest ecosystems play a crucial role in carbon cycling due to their ability to store significant amounts of carbon in plant biomass, deadwood and soil. Research on deadwood has usually focused on the analysis of the current state without considering the history of forest stands. However, a recent trend in many European countries is to increase the area and number of protected areas, often encompassing previously managed forests. Such changes in forest management affect the abundance and character of deadwood, and thus and need to be considered in the analysis of its carbon storage capacity.

The forests of Wielkopolski National Park in Poland are an excellent subject for such research. Until the end of the 18th century, they were owned by various landowners, leading to a highly diversified forest management driven by immediate needs of owners. In 1931, the first reserve, where logging was discontinued, was established. The current strict protection areas were mostly designated in 1957 when the park was legally established. Currently, strict protection mainly applies to habitats of oak-hornbeam forests Galio sylvatici-Carpinetum betuli, with other communities represented to a lesser extent.

The assessment of deadwood carbon stock (DWCstock) was performed using the data from the field survey conducted between 2017 and 2018. Deadwood was inventoried at 98 circular plots (0.04 ha) located inside 12 strictly protected areas. We distinguished five deadwood categories: standing snags, logs, stumps, branches, and twigs, and 5 decay classes. All dead trees and their parts with a minimum top diameter of 3 cm were measured. The small diameter threshold was selected due to the abundant presence of shrubs that ocurrred during the 'renaturalization' of forest ecosystems. From the measured dimensions we derived DWCstock using species- and decay-specific volume equations, wood density and carbon fraction values. The data were stored in a relational database and further processed and statistically analysed in the R environment. 

The analysis showed a high variability of DWCstock between plots (from 0.19 to 92.43tC/ha, mean 15.03tC/ha). Almost 50% of the total DWCstock was assigned the third decay stage, while 10 and 5% of DWCstock occurred in the first and last decay stage, respectively. This indicates a substantial accumulation of the deadwood after the abandonement of forest management. In 60% of cases, the dominant species of deadwood did not coincide with the dominant species of the currently living trees suggesting the changes in species composition of forest ecosystems over time. The results show deadwood can be considered as a long-term memory of forest dynamics. The work highlights the need to use multiple data sources for a better understanding of ecosystem development.