Climate sensitivity of Abies alba Mill. in marginal Mediterranean low-elevation stands reveals new insights into the ecological potential of the species

Understanding the ecological needs of forest tree species at the warm edge of their range can provide valuable information for management strategies in a warming climate. Here, we carried out a dendroecological study focusing on submediterranean and mesomediterranean low elevation (i.e., 30-800 m asl) marginal stands of Abies alba Mill. (silver fir) under warm mean July-August temperatures of 23-25 degrees C. Such marginal stands are compared to an Apennine core stand at 1450 m asl in central Italy amid the climatic niche with optimal growing conditions. Additionally, we used understory vegetation surveys to assess local growing conditions. During periods of low growth rates, the growth of low-elevation stands is significantly influenced by both short-term current-year climatic signals (monthly to seasonal; immediate effect on growth) and long-term (pluriannual) cumulative signals, whereas the strength of the climatic influence progressively increases from the monthly to the multi-annual scale. Trees are adversely affected by high summer and early autumn temperatures and drought and benefit from sufficient rainfall in late summer, autumn, and early winter, in addition to spring rainfall. Moreover, when temperature and moisture are high, low-elevation stands likely benefit from a prolonged late growing season. These findings illustrate that the growth of A. alba at low elevations is rather limited by moisture availability than high temperatures. In contrast, silver fir in the cooler and moister uppermost reference stand was less affected by current year drought and cumulative climatic effects. Our results confirm the potential of A. alba to thrive under warm climates, as previously evidenced by palaeoecological data and dynamic modelling. However, in Mediterranean ecosystems, this capacity is modulated by local growing conditions, highlighting the need for site-oriented management strategies.