Trends in the “flowering” periods of Juniperus species (Cupressaceae) in the province of Malaga (western Mediterranean) during the last six decades (1971-2023).

Abstract

Phenological studies on Juniperus are scarce. It is a genus widely distributed throughout the northern hemisphere, with species that live in diverse habitats and altitudes. The University of Malaga has a herbarium with numerous preserved sheets from Malaga province (south of the Iberian Peninsula), a biodiversity hotspot. Therefore, our main objectives were to verify whether there were sufficient sheets to study flowering trends and to detect possible effects of climate change. The herbarium specimens were carefully observed under a magnifying glass to note the presence of reproductive structures, both male and female. We have found that over the last decades (1971-2023), there has been a significant advance in the sexual reproductive phenophase of J. communis subsp. hemisphaerica, J. sabina, and J. phoenicea subsp. phoenicea at a rate of three days per year. The first two live on mountain peaks, and their blooms have been advancing from summer to spring, because of climate change. In contrast, in the case of J. oxycedrus subsp. oxycedrus, the trend was to lag rather than advance. J. phoenicea and J. oxycedrus, species widely distributed in the Mediterranean and at altitude, form unisexual cones throughout the year. A direct significant relationship was observed between the delay in cone formation and the increase in altitude for J. phoenicea and J. turbinata. These results indicate that some Juniperus species have adapted to the Mediterranean climate by flowering at any time and are more resilient to global warming (J. oxycedrus, J. phoenicea). In contrast, the mountain peak species (J. communis, J. sabina) have short flowering periods and are more sensitive to global warming.