Diversifying sub-Mediterranean pinewoods with oak species in a context of assisted migration: responses to local climate and light environment

Abstract

Questions How do thermal migration distance and extreme cold events affect seedling emergence and survival in assisted migration schemes in the sub-Mediterranean context? What role does plant provenance play? Can biotic interactions such as nurse effect of the overstorey and shrub layer buffer the negative responses to plant translocation? Are any of these effects species-specific? Location Three pinewoods in the Catalan Pre-Pyrenees, northeast Iberian Peninsula. Methods We used a replicated field trial to test the early years establishment of two contrasted provenances of four Quercus species (Q. coccifera, Q. ilex, Q. faginea and Q. pubescens) that were sown and planted along gradients of elevation and understorey microsite conditions in sub-Mediterranean pinewoods. Seedling responses to translocation were evaluated through seedling emergence, seedling survival and re-sprouting after dieback events according to seedling provenance, thermal migration distance, extreme cold events and microenvironment. Results The study reports high success of both the planting (with an overall 76.3% of initial 3-yr survival) and sowing (with an overall 50% of seedling emergence) experiments. The results show that: (1) the thermal migration distance and the occurrence of extreme cold events have strong effects on the responses of the translocated species (particularly the evergreen oaks); (2) the forest overstorey plays an important role in attenuating the negative effects of thermal migration distance on seedling survival; and (3) these responses are species-specific. The evergreen Quercus species showed more evidence of high ecotypic differentiation in terms of cold tolerance, enabling local provenances to respond better to translocation. In contrast, marcescent species, showed high phenotypic plasticity that led to a better overall establishment success. Conclusion The implementation of assisted migration is a feasible option to increase the diversity and resilience of the sub-Mediterranean pinewoods. Assisted migration programmes should manage risks by thoroughly considering thermal migration distances and the occurrence of extreme cold events when selecting species and seed sources, since Mediterranean tree species show different strategies regarding adaptation to cold. Programme managers should also consider the advantage of planting/sowing under relatively closed canopy to buffer some of the negative responses associated with translocation.

This research was primarily supported by the European MED project ‘ForClimadapt’ (Adaptation of Mediterranean woodlands to climate change) and the Spanish Ministry of Science and Innovation via the RESILFOR project (AGL2012‐40039‐C02‐01). The Catalan Agency for Management of University and Research Grants provided S.M.A. with support through a ‘pre‐doctoral’ grant (FI‐DGR) and the Spanish Ministry of Science and Innovation provided L.C. with support through a post‐doctoral ‘Ramon y Cajal’ contract. This work benefited from a short‐term scientific exchange grant provided to S.M.A. by the Marie Curie IRSES project NEWFORESTS exchange programme (financed under EU FP7). The authors thank the Catalan Government, Catalunya Caixa's Social Work, Manuel Garrabou and the residents of Cabó valley for providing access to the sites in which the experiment was set up, and to Marc Cortina, Aida Sala, Roberto Solsona, Vicent Vidal and Sergio Martínez for invaluable help in setting up and monitoring the experiment.