Large‐scale recruitment limitation in <scp>M</scp>editerranean pines: the role of <i><scp>Q</scp>uercus ilex</i> and forest successional advance as key regional drivers

Abstract Aim Large‐scale patterns of limitations in tree recruitment remain poorly described in the M editerranean B asin, and this information is required to assess the impacts of global warming on forests. Here, we unveil the existence of opposite trends of recruitment limitation between the dominant genera Q uercus and P inus on a large scale and identify the key ecological drivers of these diverging trends. Location S pain Methods We gathered data from the S panish N ational F orest inventory to assess recruitment trends for the dominant species ( P inus halepensis , P inus pinea , P inus pinaster , P inus nigra , P inus sylvestris , P inus uncinata , Q uercus suber , Q uercus ilex , Q uercus petraea , Q uercus robur , Q uercus faginea and Q uercus pyrenaica ). We assessed the direct and indirect drivers of recruitment by applying B ayesian structural equation modelling techniques. Results Severe limitations in recruitment were observed across extensive areas for all P inus species studied, with recruitment failure affecting 54–71% of the surveyed plots. In striking contrast, Q uercus species expanded into 41% of the plots surveyed compared to only 10% for P inus and had a lower local recruitment failure (29% of Q uercus localities compared to 63% for P inus species). Bayesian structural equation models highlighted the key role of the presence of Q . ilex saplings and the increase in the basal area of Q . ilex in limiting recruitment in five P inus species. The recruitment of P . sylvestris and P . nigra showed the most negative trends and was negatively associated with the impacts of fire. Main conclusions This study identified Q . ilex , the most widespread species in this area, as a key driver of recruitment shifts on a large scale, negatively affecting most pine species with the advance of forest succession. These results highlight that the future expansion/contraction of Q . ilex stands with ongoing climate change will be a key process indirectly controlling the demographic responses of P inus species in the M editerranean B asin.