Climatic drivers of growth and intra-annual wood density fluctuations in juniper species from seasonally dry environments

Shrub species are expected to substitute trees under more arid conditions but how they respond to climate variability in terms of growth and wood-anatomical features is still scarcely understood. Intra-annual density fluctuations (IADFs) are wood-anatomical features widely used to assess how woody plant species respond to climate variability in seasonally dry regions. We investigated how climatic conditions and growth form affect the radial growth responses of four juniper species ( Juniperus communis , J. oxycedrus , J. phoenicea and J. thurifera ) in Mediterranean Spain. Radial growth and the production of latewood IADFs were measured using dendrochronology. Their relationship with climate variables were also quantified in twelve sites across a continental-coastal gradient. Growth and IADF responses to climate were modulated by species, site and tree factors in juniper species. The series of ring-width indices shared more common variability than IADFs series. Age negatively affected IADF formation, while diameter increased it. Coastal junipers, mainly J. phoenicea , produced more IADFs than those dominant in continental areas such as J. communis . High autumn precipitation and low maximum temperatures enhanced IADF formation. In continental semi-arid sites, J. thurifera trees formed more IADFs and were more sensitive to autumn conditions compared to coexisting J. phoenicea shrubs. J. communis was less responsive to climate variability than J. oxycedrus , which was negatively impacted by spring-to-autumn dry conditions. J. phoenicea growth was also constrained by dry conditions, but warm early-autumn temperatures enhanced it. In conclusion, growth and IADFs production represent different measures of resilience capacity of woody species in seasonally dry environments. • Intra-annual density fluctuations (IADFs) capture growth responses to climate in four juniper species. • Age and diameter negatively and positively influenced IADFs production, respectively. • High autumn precipitation and low maximum temperatures enhanced IADF formation. • Junipers from coastal sites produced more IADFs than those from continental sites.