Minimum wood density of Juniperus thurifera is a robust proxy of spring water availability in a continental Mediterranean climate

Aim The Mediterranean Basin is considered to be a climate-change hotspot, for which rising temperatures and associated aridification have been forecast. Such trends could affect the performance and growth of conifers in these drought-prone areas. We evaluated whether radial growth and wood density can act as proxy measures of precipitation and drought in a Mediterranean conifer. Location Iberian Juniperus thurifera forests in northern and eastern Spain. Methods We sampled 10 stands encompassing J. thurifera's distributional area. We related four annually resolved tree-ring variables (earlywood and latewood width, and maximum and minimum wood density) to climatic factors (temperature, precipitation and drought index) for the period 1951-2000. We then analysed the spatial and temporal patterns of those associations. Results Of all the four tree-ring variables analysed, minimum wood density presented the strongest response to climate. Higher values of minimum wood density were related to drier spring conditions, particularly in the most xeric sites, confirming that a drought-induced reduction in the radial expansion of tracheids increases earlywood density. Main conclusions Minimum wood density is a biogeographically meaningful proxy of spring water availability for the Mediterranean conifer J. thurifera.