Climate change is expected to have profound amplified impacts on densely populated and urbanised regions such as Belgium. With this project we aim to combine advanced high resolution climate modeling with past long term (100 yrs), medium term (25 yrs) and contemporary changes in species composition and functional characteristics of plants and animals. First, a tool will be developed to produce high-resolution historical climate data for any given Belgian location, that includes urbanization and forest microclimate effects on past climate. This tool will be applied to determine the role of changes in temperature and precipitation in thermophilization and functional trait changes in the Belgian flora and arthropods, while accounting for UHI and forest buffering effects. The rich and unique natural history collection of RBIN and herbarium of MeiseBG will be used to retrieve data on species occurrences and functional traits that capture these long-term climate change events. A resurvey of forest stand characteristics and the plant and soil fauna communities in 56 highly documented forest plots along an urban-to-rural gradient in the northern part of Belgium will provide even more detailed information on climate change effects on forest ecosystem functioning, interactive effects due to urbanization, and the thermophilization of plant and animal species assemblies. The identification of the major drivers affecting community change will allow us to design sound guidelines for forest management and city planning that maximally mitigate the effect of climate change on biodiversity (and even extending to human health). Finally, to isolate the urban impact on fauna and flora, we will perform an in-depth analysis of climate change and its impacts on biodiversity in the Brussels region. We will execute very high-resolution weather model experiments over Brussels in order to provide the necessary weather data to assess how the urban heat island and urban green affects performance of plants and invertebrates in a mesocosm experiment along UHI gradients in Brussels. In sum, this project will deliver unprecedented data and tools for Belgium to (i) quantify and understand how urbanisation amplifies and trees buffer climate change as well as (ii) to assess effects on biodiversity from the 19th century to today.