Apple phenology occurs earlier across South Korea with higher temperatures and increased precipitation

This study examined relationships between temperature, precipitation, geo-topography, and the spring phenology of Fuji and Hongro apple cultivars along spatial gradients across South Korea. Phenology data was gathered from 2011 to 2014 in 42 uniformly managed research orchards which span a range in climate, latitude, and elevation. We used linear models and spatially explicit forecasts to study apple phenology under climate change scenarios. Given dry winters and complex terrain in South Korea, we hypothesized that, in addition to temperature, precipitation and geo-topographic factors influence apple phenology. We also expected responses to climate variation to be similar between (spatial) and within (temporal) orchards, given the controlled conditions and the use of apple clones in this study. With other factors held constant, phenological sensitivity ranged from - 3.2 to - 3.4 days °C^-1 for air temperature and - 0.5 to - 0.6 days cm^-1 for March precipitation in a combined model. When modeled without temperature, phenology changed by up to 10 days over the full range in March precipitation. Spring temperatures and precipitation in March had very little cross-correlation (r < 0.05), suggesting these patterns are independent; however, in a combined model including temperature, predicted changes in precipitation over the next 80 years have only a small impact on future apple phenology. Combining the best models with climate forecasts for South Korea, spring phenology continues to occur earlier over the next 80 years, mostly due to warming temperatures but with strong variation between regions. This suggests regionally specific climate change adaptation strategies are needed for future apple production in South Korea.