Ecological memory and regional context influence performance of adaptation plantings in northeastern US temperate forests

Abstract

Species distribution models predict shifts in forest habitat in response to warming temperatures associated with climate change, yet tree migration rates lag climate change, leading to misalignment of current species assemblages with future climate conditions. Forest adaptation strategies have been proposed to deliberately adjust species composition by planting climate-suitable species. Practical evaluations of adaptation plantings are limited, especially in the context of ecological memory or extreme climate events. In this study, we examined the 3-year survival and growth response of future climate-adapted seedling transplants within operational-scale silvicultural trials across temperate forests in the northeastern US. Nine species were selected for evaluation based on projected future importance under climate change and potential functional redundancy with species currently found in these ecosystems. We investigated how adaptation planting type (‘population enrichment’ vs. ‘assisted range expansion’) and local site conditions reinforce interference interactions with existing vegetation at filtering adaptation strategies focused on transitioning forest composition. Our results show the performance of seedling transplants is based on species (e.g. functional attributes and size), the strength of local competition (e.g. ecological memory) and adaptation planting type, a proxy for source distance. These findings were consistent across regional forests but modified by site-specific conditions such as browse pressure and extreme climate events, namely drought and spring frost events. Synthesis and applications. Our results highlight that managing forests for shifts in future composition represents a promising adaptation strategy for incorporating new species and functional traits into contemporary forests. Yet, important barriers remain for the establishment of future climate-adapted forests that will most likely require management intervention. Nonetheless, the broader applicability of our findings demonstrates the potential for adaptation plantings to serve as strategic source nodes for the establishment of future climate-adapted species across functionally connected landscapes.