Unveiling the springtime phenological strategies in permafrost vegetation

The springtime phenology in permafrost regions of the Northern Hemisphere is exhibiting an extensive advance in response to climate change that is considered to be primarily driven by the rising temperature that vastly exceeds the average rate of global warming. This phenological trend emerges as the result of spatial variability in temperature and the response of vegetation to temperature (referred to here as the temperature sensitivity (S_T) of phenology, change in phenological timing per unit change in temperature). In contrast to the more well-defined pattern of temperature variability, far less is known about the temperature sensitivity of vegetation phenology. Further, the above-average and highly heterogeneous warming in permafrost regions leads to changes in chilling exposure, frost risk, and other key controllers of temperature sensitivity, potentially allowing plants to adapt their phenological strategies. However, these phenological strategies  have not been investigated yet at the pan-Arctic scale in models or observations.

Here, we seek to combine remote sensing-based and process model-based approaches to reveal the spatiotemporal pattern and strategic mechanisms regarding the S_T of springtime phenology. To obtain generalisable dependencies, remote sensing retrieved phenology, climate data and soil physical property data are used to explore the linkages between S_T and temperature and permafrost drivers, providing insights on vegetation phenological strategies. The novel QUINCY model is then adopted at site levels to validate the plausibility of possible strategies. Sets of model experiments with respect to varying biological and environmental factors are applied to elucidate the major controllers. Results shed light on the importance of environmental variability, and provide a more elaborate explanation for the S_T variability of spring-time phenology.