Zoltan Kun’s research while affiliated with Frankfurt Zoological Society and other places

Carbon accounting in the land sector requires a reference level from which to calculate past losses of carbon and potential for gains using a stock-based target. Carbon carrying capacity represented by the carbon stock in primary forests is an ecologically-based reference level that allows estimation of the mitigation potential derived from protecting and restoring forests to increase their carbon stocks. Here we measured and collated tree inventory data at primary forest sites including from research studies, literature and forest inventories (7982 sites, 288,262 trees, 27 countries) across boreal, temperate, and subtropical Global Ecological Zones within Europe. We calculated total biomass carbon stock per hectare (above- and below-ground, dead biomass) and found it was 1.6 times larger on average than modelled global maps for primary forests and 2.3 times for all forests. Large trees (diameter greater than 60 cm) accounted for 50% of biomass and are important carbon reservoirs. Carbon stock foregone by harvesting of 12–52% demonstrated the mitigation potential. Estimated carbon gain by protecting, restoring and ongoing growth of existing forests equated to 309 megatons carbon dioxide equivalents per year, additional to, and higher than, the current forest sink, and comparable to the Green Deal 2030 target for carbon dioxide removals.

Forests are critical for biodiversity conservation and climate change mitigation: reducing emissions, increasing removals, and providing resilient ecosystems with stable long‐term carbon storage. However, evaluating the mitigation effectiveness of forests managed for conservation versus commodity production has been long debated. We assessed factors influencing evaluation of mitigation effectiveness––land area, time horizon, reference level, carbon stock longevity––and tested the outcomes using analyses of carbon dynamics from an Australian ecosystem. Results showed that landscape scale accounting using carbon carrying capacity as the reference level and assessed over a series of time horizons best enables explicit evaluation of mitigation benefits. Time horizons need to differentiate between near‐term emissions reduction targets (2030 and 2050), relative longevity of carbon stocks in different reservoirs, and long‐term impacts on atmospheric CO2 concentration. Greatest mitigation benefits derive from conservation through continued forest growth (52% gain in carbon stock by 2050) and accumulating carbon to attain carbon retention potential (70% gain). Cumulative emissions from harvesting result in permanent elevation of atmospheric CO2 concentration (32 times the annual emission by rotation end). We recommend these time horizons and landscape scales for evaluating forest management to better guide policies and investments for achieving climate mitigation and biodiversity conservation.

Primary forests, defined here as forests where the signs of human impacts, if any, are strongly blurred due to decades without forest management, are scarce in Europe and continue to disappear. Despite these losses, we know little about where these forests occur. Here, we present a comprehensive geodatabase and map of Europe’s known primary forests. Our geodatabase harmonizes 48 different, mostly field-based datasets of primary forests, and contains 18,411 individual patches (41.1 Mha) spread across 33 countries. When available, we provide information on each patch (name, location, naturalness, extent and dominant tree species) and the surrounding landscape (biogeographical regions, protection status, potential natural vegetation, current forest extent). Using Landsat satellite-image time series (1985–2018) we checked each patch for possible disturbance events since primary forests were identified, resulting in 94% of patches free of significant disturbances in the last 30 years. Although knowledge gaps remain, ours is the most comprehensive dataset on primary forests in Europe, and will be useful for ecological studies, and conservation planning to safeguard these unique forests.

The carbon stock in Europe's forests is decreasing and the importance of protecting ‘unmanaged’ forests must be recognised in reversing this process. In order to keep carbon out of the atmosphere and to meet the Paris Agreement goals, the remaining primary forests must be protected and secondary forests should be allowed to continue growing to preserve existing carbon stocks and accumulate additional stocks. Scientific evidence suggests that ‘unmanaged’ forests have higher total biomass carbon stock than secondary forests being actively managed for commodity production or recently abandoned. image