The influence of global climate change is most pronounced in high-latitude ecosystems, and the vegetation phenology there provides an early indicator of environmental response. Sweden serves as a natural laboratory for analysing vegetation responses to climate change due to its pronounced north-south environmental gradient, including temperate, boreal, and alpine tundra biomes alongside complex land-use scenarios. Nevertheless, a systematic study of spatiotemporal vegetation phenology patterns across Sweden and their connection with ecosystem processes remains a significant scientific gap.
This study aimed to systematically examine spatiotemporal trends in vegetation phenology and canopy structure (Leaf Area Index, LAI) across Sweden from 2001–2022, elucidate the patterns of the coupling and decoupling between these changes and a key ecosystem function (Gross Primary Productivity, GPP), and finally, identify and quantify the primary climatic and non-climatic drivers of GPP's inter-annual variability. For this study, a comprehensive suite of satellite-based remote sensing datasets from 2001–2022 were integrated, including vegetation phenology metrics, canopy structure, climate variables, and GPP. Phenology extraction tools and a machine learning model XGBoost were employed to conduct a spatiotemporal trend analysis, uncover non-linear relationships between variables, and quantify the relative influence of different drivers on GPP.
Our results reveal two spatially distinct phenological patterns: central and southern Sweden experienced an earlier spring phenology and a strong increase in LAI (synergistic improvement), while the northwestern alpine and high-latitude areas demonstrated strong canopy greening despite a delayed spring phenology (compensatory growth). Crucially, this paper reveals a significant decoupling between canopy greening and ecosystem productivity, which is termed ‘ineffective greening’, wherein greening in compensatory growth areas failed to translate into a corresponding increase in GPP. It is also worth noting that while energy-related variables such as temperature and solar radiation were not the dominant drivers of short-term GPP variability, water availability, in the form of lagged precipitation and soil moisture did.
These findings both characterize complex nonlinear responses of high latitude ecosystems to global change and help guide regional ecosystem model development and adaptive management decision-making.
