Distinct Functioning of Low- Versus High-Altitude Refugia in the Mediterranean: Inferences From Life-History Traits of Two Related Relict Trees From the Islands of Sicily and Crete

Aim

Relict trees are the outcome of long-term ‘natural experiments’. Accordingly, they provide opportunities to study the effects of local adaptation of trees, which are still poorly understood but crucial in the context of climate change. In turn, the physical settings of refugia at macro- and microscale are the key drivers of the environmental adaptability of such species. Using two congeneric climate relict trees (Zelkova sicula and Z. abelicea) as model species, we analysed the functional relationships between tree growth patterns and the distinctive environmental drivers of low- versus high-altitude refugia in the Mediterranean.

Location

Mediterranean islands of Sicily (Italy) and Crete (Greece).

Methods

To evaluate the growth potential of the two relict trees we used top height and multi-year data of shoot length over the entire distribution range of both species. Growth form and height growth dynamics of Z. sicula were also investigated by stem analysis. Moreover, tree-ring response to climate was compared through classical dendrochronological approaches.

Results

Tree size, as well as shoot and radial growth are notably greater in Z. abelicea, suggesting this species better fits in its habitat and the higher-elevation Cretan refugia are less constraining than their low-elevation Sicilian counterparts. Tree-ring growth response to precipitation and evapotranspiration is rather similar between the two species and points to the key role of moisture balance on growth. However, the 1-month delay in the response from the Sicilian to the Cretan relict mirrors the differential role of altitude against micro-topography in decoupling from the regional climate.

Main Conclusions

The significant attenuation of environmental constraints due to the ‘elevation effect’ is a major offsetting driver for the distinct functioning of low- versus high-altitude refugia in the Mediterranean, but macroclimatic patterns may locally blur the effectiveness of refugia in a long-term conservation perspective.