Climate change adaptation with non-native tree species in Central European forests: early tree survival in a multi-site field trial

Climate projections indicate large increases in temperature, requiring tree species to adapt or migrate faster than observed historic rates. In Central Europe, discussion in forest management has increasingly focused on how humans can assist these adaptation/migration processes, especially when important forest ecosystem services are at risk. One option is to introduce non-native tree species to help forest ecosystems adapt to climate change. We established a long-term experiment in autumn 2012 on five study sites in climatically different regions of Central Europe. The performance of five non-native tree species from warmer climates (Abies bornmuelleriana Mattf., Cedrus libani A. Rich., Fagus orientalis Lipsky, Tilia tomentosa Moench and Tsuga heterophylla Sarg.) was compared to that of one local species native to each site. We monitored sapling survival during the first 4 years after planting. Small differences in timing of inventory campaigns were overcome by fitting a Weibull function to survival curves and analysing time-harmonized estimates for equal biannual periods. Sapling mortality decreased over time, but early after planting, it differed between species. The native and the two non-native broadleaved species showed higher survival than the non-native coniferous species. Moreover, the site conditions of the open areas seemed to initially hamper the growth of shade-tolerant species. All species performed reasonably well during the relatively short observation period. Any differences between hazard rates almost vanished 4 years after planting, which suggests that all species tested are likely to thrive under current climate conditions. Long-term observations are, however, needed to corroborate these results.