Arboreal and prostrate conifers coexisting in Mediterranean high mountains differ in their climatic responses

[EN] In contrast to most high elevation areas, plant growth at Mediterranean mountains is exposed to a summer drought period, which represents an additional climatic constraint to low temperatures. Although arboreal and shrubby conifers coexist at high altitudes, most dendroecological studies have focused on climatic responses of tree species, whereas those of shrubby species remain mostly unexplored. We built tree-ring width chronologies for two conifer species, a shrub (Juniperus sabina) and a tree (Pinus sylvestris), coexisting at three high-altitude localities of the Iberian System mountains, eastern Spain. We analyzed their climate-growth relationships for the period 1950-2009 using correlation analyses and multiple regressions. Coexisting species responded to year-to-year climatic variability in different ways. Radial growth in junipers and pines responded positively to April and May temperatures, respectively. Summer drought constrained growth in both cases, although its impact was stronger on junipers than on pines. Our findings suggest that junipers respond earlier than pines to spring temperatures due to their prostrate morphology which may enhance a fast warming of their cambial meristems after snowmelt. The higher dependence of . J. sabina on summer rainfall as compared with co-occurring pines confirms that drought stress negatively impacts secondary growth in Mediterranean mountains. This sensitivity to water availability may be caused by the juniper shallow root systems, which mainly use superficial soil water. The climatic signal registered in . J. sabina allows studying the response of other similar shrubby woody species growing in Mediterranean alpine areas to the ongoing climate warming, which could also reduce water availability. © 2012 Elsevier GmbH.We thank Natural Parks of Moncayo and Alto Tajo for the permissions to make the field work, specifically to Enrique Arrechea and Ángel Vela respectively. Rafael Jiménez helped us to find the best places for sampling in Moncayo. We thank Erik Rodríguez, Rafael Jiménez and Juan Manuel Gil for helping us in the field, Natali Bascopé for her participation in the laboratory work and Juan Carlos Rubio for his assistance at CESEFOR with sample processing. A previous version was improved by C. Woodhouse and two anonymous referees’ comments. This work was supported by a grant FPI-MICINN to AIGC and projects CGL2009-13190-C03-03 (Spanish Ministry of Science and Innovation) and VA006A10-2 (Junta de Castilla y León). JJC acknowledges the support of ARAID.Peer Reviewe