The largest European forest carbon stocks are in the Dinaric Alps old-growth forests: comparison of direct measurements and standardised approaches

Carbon sinks and stocks are among the most important ecosystem services provided by forests in climate change mitigation policies. In this context, old-growth forests represent an essential reference point for the development of close-to-nature silviculture, including carbon management techniques. Despite their small extent in Europe, temperate old-growth forests are assumed to be among the most prominent in terms of biomass and carbon storage. However, monitoring and reporting of their carbon stocks is still poorly understood. To better understand the amount and distribution of carbon stocks in temperate old-growth forests, we estimated the carbon stocks of two old-growth stands in the Dinaric Alps applying different assessment methods, including direct and indirect approaches (e.g., field measurements and allometric equations vs. IPCC standard methods). This paper presents the quantification and the distribution of carbon among the five main forest carbon pools (i.e., aboveground, belowground, deadwood, litter, and soil) in the study areas and the differences between the applied methods.

Our findings show a very prominent C stock in both study areas (507 Mg C ha^-1), concentrated in a few large diameter trees (36% of C in 5% of trees in number). Furthermore, we found significant differences between C stock estimation methods, both between direct and indirect approaches, which tended to underestimate or overestimate depending on the pool considered, and within the direct methods.

The comparison of our results with previous studies and data collected in other European old-growth forests highlights the importance of temperate forests, among which the Dinaric Alps old-growth forests are the most prominent. These results provide an important benchmark for the development of future approaches to the management of the European temperate forests.