Recent model projections and many research results across the world suggest that forests could be significant carbon sinks or sources in the future, contributing in a such a way to global warming mitigation. Conversion of coppice forest to high forest may play an important role towards this direction. This study deals with the estimation of biomass, carbon pool and accumulation rates in all IPCC biomass categories of a 77 year-old oak ecosystem, which has been subjected to conversion from coppice to high forest through repeated tending measures. The research includes a plethora of field tree measurements, destructive sampling of representative oak trees and a systematic sampling of dead wood (standing and fallen), litter and soil. Furthermore, for the estimation of above ground tree living biomass at the stand level, we developed and tested appropriate allometric biomass equations based on the relationships between various independent tree variables (morphological characteristics) and the different tree biomass compartments or leaf biomass. Data analysis shows that coppice conversion results in large accumulation of carbon in all ecosystem pools, with an average annual carbon rate accumulation of 1.97 Mg ha–1 in living above and below ground tree biomass and small amounts to dead wood and litter. The developed allometric equations indicate that above ground tree living biomass can be reliable and precisely predicted by the simple measurement of tree diameter.

The recent Glasgow Climate Pact has recognized the contribution of ecosystems as sinks and reservoirs of greenhouse gases and their importance to achieve the objective of a maximum temperature increase of 1.5 °C. Thus, the knowledge of the long-term storage capacity of the soil organic carbon (C) in forest soils, and the driving factors, are considered of great importance for the mitigation of global climate changes. A database of published data in a ‘grey’ Greek bibliography, concerning the long-term storage of soil organic C in soil profiles for Greek forests, was compiled, including 307 full soil profiles, distributed between 21 types of forest ecosystem throughout the country (Greece). The data collected concerned the amount of long-term stored carbon in the full soil profile, per soil horizon, up to the uncracked bedrock. These also contained information on the sampling location, the type of forest ecosystem, the soil depth, the type of land management, the forest origin, the floristic zone, the altitude, and the climate type. According to the results analysis, the average soil organic C stored was 108.19 Mg ha−1, and ranged greatly between 11.49 and 409.26 Mg ha−1. The type of forest ecosystem, soil depth, land management practices, forest origin, floristic zone, and climate type played an important role in the carbon sequestration process, greatly influencing the long-term amount of stored carbon. Under the demands for mitigating climate change and reducing the rates of global warming, data evaluation indicates the directions to be followed for increasing the long-term storage of carbon, named systematic forest management, and the exclusion of the drivers responsible for the low carbon storage of soil, such as human pressure and overgrazing. Restoration actions such as reforestation and rehabilitation of the degraded forest ecosystems, which were found to store low carbon amounts, can be also considered as effective tools for increasing the long-term carbon storage in forest ecosystems.

Forests host important plant biodiversity. Nevertheless, due to climate change and human disturbances, the floristic quality of forest ecosystems is degraded. Greek peri-urban forests biodiversity is threatened by anthropogenic activities such as forest fragmentation, pollution, garbage, etc. Measurement of biodiversity status and the floristic quality assessment can be used to estimate the degree of forest degradation caused by anthropogenic disturbances. In this study, we compared and evaluated six forest ecosystem types in the peri-urban forests of Thessaloniki, northern Greece, by using Shannon’s biodiversity index as well as and α and β diversity Sørensen indices. Furthermore, we recorded the prevailing anthropogenic disturbances and compared the plant families and the ruderal species appearing in each forest ecosystem. Finally, the average conservatism value (C value) of the plant species found in each ecosystem was determined in order to calculate the ecosystem floristic quality index. Analysis of the results showed that the floristic and ecological parameters tested greatly vary among ecosystems. Broadleaf forests of higher altitude hosted the greatest biodiversity, and the higher floristic quality index and plant conservation value. On the contrary, most disturbances and most ruderal species were recorded in ecosystems of lower altitude, adjacent to the city (Pinus brutia forest and Maqui vegetation), the least disturbed ecosystems were found in the steep slopes (Castanea sativa forest). Most ruderal species found belonged to the Asteraceae and Rosaceae families. Accessibility and attractiveness of stands were positively correlated with disturbances. Insufficient management, lack of protection measures, and littering removal contribute to the increase in the level of disturbance.