Climatic events inducing die-off in Mediterranean shrublands: are species’ responses related to their functional traits?

Francisco Lloret, Enrique G. de la Riva, Ignacio M. Pérez-Ramos, Teodoro Marañón, Sandra Saura-Mas, Ricardo Díaz-Delgado, Rafael Villar

Extreme climatic episodes, likely associated with climate change, often result in profound alterations of ecosystems and, particularly, in drastic events of vegetation die-off. Species attributes are expected to explain different biological responses to these environmental alterations. Here we explored how changes in plant cover and recruitment in response to an extreme climatic episode of drought and low temperatures were related to a set of functional traits (of leaves, roots and seeds) in Mediterranean shrubland species of south-west Spain. Remaining aerial green cover 2 years after the climatic event was positively related to specific leaf area (SLA), and negatively to leaf water potential, stable carbon isotope ratio and leaf proline content. However, plant cover resilience, i.e. the ability to attain pre-event values, was positively related to a syndrome of traits distinguished by a higher efficiency of water use and uptake. Thus, higher SLA and lower water-use efficiency characterized species that were able to maintain green biomass for a longer period of time but were less resilient in the medium term. There was a negative relationship between such syndromes and the number of emerging seedlings. Species with small seeds produced more seedlings per adult. Overall, recruitment was positively correlated with species die-off. This study demonstrates the relationship between plant traits and strong environmental pulses related to climate change, providing a functional interpretation of the recently reported episodes of climate-induced vegetation die-off. Our findings reveal the importance of selecting meaningful traits to interpret post-event resilience processes, particularly when combined with demographic attributes.