Drought responses of Italian silver fir provenances in a climate change perspective

Abstract

In a climate change perspective, the resilience of Mediterranean forest ecosystems is closely linked to their ability to cope with drought and rising temperatures. This ability can be influenced by genetic differences between and within species or provenances. In a changing environment, management guidelines should weight the risks associated both to local and/or non-local provenances, to promote the effective conservation and sustainable management of resilient forest genetic resources. In this study, we analysed the growth responses to drought of silver fir (Abies alba) in the Tuscan-Emilian Apennine National Park in natural and planted forests, comparing the growth performance of three provenances of this species in Italy: (a) Western Alpine - (b) Northern Apennine (local) - (c) Southern Apennine. Drought severity was defined by the Standardised Precipitation-Evapotranspiration Index (SPEI). We carried out dendrochronological analyses by assessing climate-growth relationships and applying drought 'resilience indices' (RRR) based on tree ring width. Planted forests showed faster mean growth than highly fragmented natural forests, higher resilience to severe drought and significantly higher recovery to severe drought. Fir provenances do not differ in mean growth rate, while the Southern Apennine provenance showed significantly better recovery (rec) and resilience (resl) especially compared to the Western Alpine provenance during moderate (rec +5–15%, resl +13–15%) and extreme (rec +20% %, resl +22%) drought years. The local provenance showed an intermediate behaviour. Southern and local provenances showed higher resilience to drought compared to the Western Alpine one, proving to be very important forest genetic resources in the context of climate change response strategies. Finally, the RRR indices trends calculated on the years identified by SPEI6 generally showed greater differences between provenances and regeneration modes than on the years identified by SPEI12, possibly due to the increase in recurrent short-duration droughts in mountainous contexts during the growing season. These results provide important information on the drought response of different silver fir provenances under climate change, highlighting the importance of taking into account the genetic background of forest reproductive materials in forest management and planning. Thanks to the close collaboration with the National Park and local forest managers, these results may find concrete application, e.g., by properly evaluating the usefulness of provenance assisted migration in the National Park forests and providing better management of remnant silver fir natural forests.