Tree Times: Urban Plants as Timekeepers and Seasonal Indicators

Abstract

As living beings that change with the seasons, urban trees both indicate and structure time in the city. They do so through their own agency and life cycles and through the care and management they require in urban environments where they often stand in conflict with other land uses. In temperate zones, urban trees have been planted for centuries especially to provide cooling shade in hot summers. Their changeable and seasonal aesthetic effects, including their color, form, sound, and smell, have not only fostered individual urban identities but also impacted human psychological wellbeing. Focusing on cities in the temperate climate zone in the nineteenth and twentieth centuries, this article shows how some tree species were bred and introduced in urban areas to create seasonal effects, while others were eliminated or manipulated to avoid unwanted seasonal characteristics. Scientists and citizen scientists from an early time onwards considered urban trees as indicators of seasonal variations of the urban climate and of the urban heat island effect. Urban tree phenology transgressed the popular Western notion of the four seasons by offering a more nuanced structure of the year. It also revealed variations of seasonal change as climate change, and it anticipated that the trees growing in our future cities will likely be of different species.