Trees are greening sooner than they should be, and new data shows why

Lin Meng won the grand prize for 2021's Science & SciLifeLab Prize for Young Scientists for her research into how city environments impact tree phenology.

"Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonal and interannual variations in climate, as well as habitat factor," according to Wikipedia. Meng set out to determine how global warming and bright artificial lighting conditions in cities changed when trees started growing leaves in spring.

Previous research has shown that higher temperatures impact vegetation growth in cities, so the following question is how global warming affects that. Meng analyzed satellite data spanning 2001 to 2014 and 85 cities in the United States to find when trees began growing leaves. Trees "greened up" an average of six days earlier and were responding more rapidly to climate change in urban areas than in rural areas.

Using data from NASA's Black Marble satellite, which measures artificial light in cities, along with phenology data from the USA National Phenology Network, Ming could also determine how lighting conditions were impacting green-up times for trees in American cities. In the most extreme cases, green-up occurred nine days sooner than expected. Ming suggests artificially extended day length due to urban lights leads to earlier spring greening of vegetation in cities, exacerbating the already early greening due to warming cities.

You can read more from Lin Meng's study published in Sciencehere.