The autumn phenology of deciduous forests and its underlying processes are a complex puzzle that is yet to be fully understood. The role of environmental factors such as temperature, water availability, and photosynthetic capacity remains unclear. Moreover, the variety of measurement methods adds another layer of complexity, creating additional uncertainty in the analyses. 

The study by Simon Kloos, Anne Klosterhalfen, Alexander Knohl & Annette Menzel investigates the processes that influence deciduous phenology in autumn using four different measurement methods: satellite images, camera images, in-situ visual observations and data on the photosynthetic activity of the forest. The data were collected in the Hainich National Park, a German beech forest, from 2000 to 2020 for leaf unfolding, leaf colouring and leaf fall. 

The analyses revealed that, in general, later leaf colouring and dieback of the leaves can be observed in warm and dry years. However, it was striking that these results can vary greatly depending on the measurement method used. This finding underscores the importance of combining all available data sources for general statements on trends and drivers of autumn phenology.