Sessile oak forest plant community changes on the NE Iberian Peninsula over recent decades

AimsOur aims were 3-fold: (i) to determine whether global change has altered the composition and structure of the plant community found in the sessile oak forests on the NE Iberian Peninsula over the last decades, (ii) to establish whether the decline in forest exploitation activities that has taken place since the mid-20th century has had any effect on the forests and (iii) to ascertain whether there is any evidence of impact from climate warming.MethodsWe assess changes in the plant community by comparing a current survey of sessile oak forest with a historical data set obtained from previous regional studies dating from 1962 to 1977. We analyse the regional changes in the community in terms of biodiversity variables, species composition and plant traits. Furthermore, plants traits such as plant life forms and chorological groups are used to discern any effects from land-use changes and climate warming on the plant community.Important FindingsThere has been a loss of diversity in the community and, in the hottest region, there is also a loss of species richness. The composition of the community suggests that, although significant changes have taken place over recent decades, these changes differ between regions as a result of the low impact global change has had in the western regions. For instance, while the tree canopy cover in the western sessile oak forests remains stable, the eastern sessile oak forests are still recovering from the former exploitation that led to a loss of their rich and abundant herbaceous stratum. In fact, the recovery process in the Catalan Pre-Coastal Range has constituted an increase in the Euro-Siberian plants typical to this community. Moreover, in the eastern forests, there is evidence that climate warming has impacted the thermophilization of the sessile oak forests found on the Coastal Range.