Tree growth response to recent warming of two endemic species in Northeast Asia

The impact of climatic change on forest ecosystems has received considerable attention, but our understanding of the modulation of this impact by elevational differences and by species interaction is still limited. Here, we analyse tree-ring-based growth-climate relationships for two dominant tree species along an 800-m elevational gradient on Jeju Island, South Korea. Both species, broadleaf Quercus mongolica (QUMO) and coniferous Abies koreana (ABKO), grow at the southern end of their distributional range and they have adjacent altitudinal ranges. We use static and moving bootstrapped correlation analysis to identify the effect of recent warming on their growth. QUMO is primarily positively influenced by moisture during the previous autumn at its upper elevational distribution. Recent warming, however, has diminished this relationship, while the enhancing impact of warm and dry summer conditions on QUMO growth has increased. These recent shifts in growth-climate relationship suggest an upward migration potential for QUMO due to warming-enhanced growth at higher elevations. ABKO growth, on the contrary, is primarily reduced by high winter and summer temperatures. This negative relationship has become more explicit in recent decades, particularly at lower elevations. At the highest elevation, however, ABKO growth-temperature relationship has consistently become more positive in the most recent decades. In the elevational zone where ABKO and QUMO co-exist, warming plays a primary role in ABKO growth reduction, while QUMO growth increases and thus induces a potential upward migration of QUMO. This combined effect can lead to population decline of ABKO. Our results significantly enhance our understanding of the impact of climate warming on two interacting species and provide information necessary for adaptation strategies to preserve declining ABKO populations.