The path towards old-growthness of the forests of Spain is slowed down as climate change intensifies

Old-growth or mature forests are main drivers of biodiversity and provide unique ecosystem services. However, due to historical human management, European forests are mainly dominated by young stands, with old-growth forests being almost nonexistent. Understanding how these secondary forests develop back towards old-growthness and what factors affect this development can contribute significantly to the conservation efforts of the scarce mature forests. Based on the idea of the development cycle, we have categorized the plots of the three consecutive Spanish National Forest Inventories spanning three decades into eight sylvogenetic phases. This novel approach has allowed us to gain important insights on the development of forests in Spain. First, we have shown how historical management legacies still shape most forests of Spain, which show structures typical of very young forests, with mature phases virtually nonexistent. Despite this, during the span of the study, most forests have shown an advance in their development cycle. However, this advance seems to be slowing down in the recent years. The analysis of several anthropic and natural factors indicates that this deceleration seems correlated with an increase of the effects of climate change, in particular with the intensification of drought spells that forests are suffering. Given the expected intensification of droughts and other perturbations derived from climate change, we can expect that the natural development of Spanish forests will continue to slow down and even suffer further regression, thus slowing or impeding their path towards maturity.