Climate responses of long-lived woody species from the comfort zone to the outposts struggling for life

Climate change is expected to cause profound effects in ecosystem structure, function, and distribution, particularly affecting long-lived woody species and forests, which will have to shift their distribution range to keep pace with relevant environmental changes. To address this challenge, new conservation strategies such as assisted migration must be implemented. However, effectively translocating woody species requires a thorough understanding of how forests respond to climate fluctuations throughout their distribution range. This thesis aims to advance our knowledge in supporting the development of crucial conservation strategies by investigating growth patterns, ecophysiological strategies for coping with climate variability, and climate-growth relationships of long-lived woody species across their distribution range. The thesis, based on a retrospective approach that combines dendrochronology and dendroanatomy, is divided into three key research lines: i) assessment of the growth performance and climate sensitivity of several species within and outside their natural distribution range, ii) evaluation of climate-growth relationships and xylem structure in target species under optimal conditions, and iii) analysis of the climate responses of long-lived woody species at the edges of their distribution range, while assessing their suitability as proxies for climate reconstruction. At the edges of the distribution, in Iceland, contrasting responses were found among species (Juniperus communis, Betula nana, Salix lanata, Betula pubescens, Sorbus aucuparia, Picea abies, and Pinus contorta) living under similar environmental conditions, underscoring the importance of species-specific ecological assessment for conservation strategies. Within the comfort zone, Picea mariana, a species native to present-day Canada, was analyzed by applying dendroanatomical techniques. Photosynthesis and carbon allocation were correlated to xylem traits, revealing a strong relationship between these two mechanisms. These dendroanatomical techniques were then analyzed in detail, comparing different approaches for dataset development and highlighting the high similarity between the two main protocols currently used in laboratories. Focusing on common juniper at the edge of its distribution range, this taxon revealed great potential as a paleoclimatic proxy, being identified as the oldest non-clonal shrub ever recorded in the tundra biome. Thanks to this unique characteristic, a reconstruction of July ground frost frequency for the past 1,200 years was possible. It showed a drastic reduction in frost frequency in the last century and, for the first time since the Viking Age, the complete absence of this phenomenon in 2021. These findings provide a high-resolution, long-term, spatially comprehensive perspective on long-lived woody species’ growth habits. They offer insights into the ecophysiological strategies, and climate sensitivity of these species from the comfort zone to the outposts of their distribution ranges, offering insights into how certain forest woody species may respond to future climate scenarios. This thesis emphasizes the importance of these lines of research for the near future, while providing a sound foundation for crucial management strategies such as assisted migration.