Differential phenological responses to temperature among various stages of spring vegetation green-up

Vegetation green-up is occurring earlier due to climate warming across the Northern Hemisphere, with substantial influences on ecosystems. However, it is unclear whether temperature responses differ among various green-up stages. Using high-temporal-resolution satellite data of vegetation greenness and averaging over northern vegetation (30-75 degrees N), we found the negative interannual partial correlation between the middle green-up stage timing (50% greenness increase in spring-summer) and temperature (RP = -0.73) was stronger than those for the onset (15% increase, RP = -0.65) and end (90% increase, RP = -0.52) of green-up during 2000-2022. Spatially, at high latitudes, the middle green-up stage showed stronger temperature responses than the onset, associated with greater low-temperature constraints and stronger control of snowmelt on green-up onset as well as greater spring frost risk. At middle latitudes, correlations with temperature were similar between the onset and middle stages of green-up, except for grasslands of the Mongolian Plateau and interior western USA, where correlations with temperature were weaker for the middle stage due to water limitation. In contrast, the end of the green-up showed weaker temperature responses than the middle due to insufficient water and high climatic temperature during the end of the green-up in most of the study region, except for cold regions in the interior western USA, western Russia and the Tibetan Plateau, where temperature was still a main driver during end of green-up. Our findings underscore the differences in temperature responses among green-up stages, which alters the temporal alignment between plants and environmental resources.