Large solitary trees (LSTs) are recognised for their ecological significance and disproportionately contribute to biodiversity and ecosystem functioning. In agricultural and urban landscapes, they serve as islands with their own microenvironment: they harbour important parts of local biodiversity, contribute to carbon stocks and nutrient cycling, and cool the local microclimate. LSTs, however, decline across the world due to climate change (warming, droughts and heat waves), pests and pathogens, disturbance, and other causes. Here we will study LSTs and their associated biodiversity and functions across Europe, as early warning signals of climate change before they occur elsewhere. LSTs may indeed be more susceptible to climate change than trees in a buffered forest context, and effects may cascade onto other trophic and biological levels. We aim to quantify, better understand and predict how LSTs’ potential performance and survival declines in the face of climate change will alter future associated biodiversity and ecosystem functioning. By using wide spatiotemporal environmental gradients of climate and urbanisation across Europe, we will be able to project these contributions across spatiotemporal scales under current conditions and future scenarios. We will provide the first integrative study on LSTs and their benefits and this will reshape our current understanding of the impacts of climate change on large trees.