Harvesting effects on forest condition indicators across Iberian forests: Implications for the EU Nature Restoration Regulation

Abstract

O_LIForest degradation is posing a growing threat to biodiversity conservation, climate regulation and nature contributions to people worldwide. The EU Nature Restoration Regulation (NRR) recognise the need of healthy forests and has established indicators to assess the condition of forest ecosystems. Forest management practices, especially harvesting may contribute to improve these indicators by, for example, reducing tree density and promoting tree species diversification. C_LIO_LIHere, we assessed temporal trends in forest condition indicators (hereafter, indicators) across Iberian forests since the 80s and evaluated how harvesting occurrence and intensity modulated these trends. Using 46,354 plots from the Spanish Forest Inventory (1986-2022), we analysed trends in indicators depending on stand diversity (monospecific or mixed), protection status (protected or unprotected), origin of the stand (natural or planted), and biogeographical region (Mediterranean or temperate). C_LIO_LIOverall, indicators increased over time. Harvesting occurrence reduced the increases in aboveground carbon stocks, structural diversity, tree species diversity, and standing deadwood; however, it contributed to increase the proportion of native species in specific forest types. Medium to high harvesting intensity negatively impacted aboveground carbon stocks, while medium intensities increased tree species diversity but reduced the structural diversity. C_LIO_LISynthesis and applications. Our results suggest that indicators are increasing as stand develops in absence of disturbances such as harvesting. Tree harvesting cannot be considered as a silver bullet to achieve the objectives of the NRR, but it can contribute under certain conditions - specifically at low intensities for carbon stocks and at medium intensities for species diversity. The naturally positive trend of indicators underlines the need to establish thresholds values and minimum rates of changes that distinguish restoration outcomes from natural dynamics. Finally, our study also highlights the key role of forest inventories in monitoring forest condition over time and across diverse landscapes. C_LI