Precipitation dominates the growth of common hornbeam (Carpinus betulus L.) and stinking juniper (Juniperus foetidissima Willd) in Arasbaran forests of northwestern Iran

Key message

European hornbeam has a great potential for tree-ring based research when using a combination of conventional dendrochronological techniques and fluorescent microscopy.

Abstract

Arasbaran forests are among the most important ecological areas in Iran, but they have been studied less extensively in comparison to the famous Hyrcanian forests. For the first time, the potential of two dominant species in these forests, i.e. hornbeam (Carpinus betulus) and stinking juniper (Juniperus foetidissima) to study the climate-growth relations was evaluated using a dendroecological approach. Difficulties in distinguishing ring-width boundaries of hornbeam were overcome using fluorescence microscopy. The statistics used to evaluate the chronologies of both species confirmed their capability to study climate–growth relationships and their potential for developing regional climate reconstruction. Hornbeam and juniper showed similar climate-growth relationships. Across all sampling sites, the growth index displayed a positive correlation with precipitation and SPEI drought index, and a negative correlation with temperature. Precipitation in spring and early autumn played a significant role in stimulating the radial growth of the species. However, topography and microclimate could affect the relationship between growth and regional climate, as the highest elevation site receives abundant moisture input from frequent fog events. Our initial study highlights the potential of hornbeam as a widely spread but neglected species in the Northern Hemisphere for dendroecological studies. Furthermore, we conclude that despite some variance in the microclimate of different sites (ranging from cold, sub-humid to warm, semi-arid) within the Arasbaran region, trees of different species in the entire study area show a common response to climatic change, mainly affected by water availability.