Spring leaf out timing in urban areas is biased by genetics

What is it about?

We use urban heat islands as a proxy for warming all the time in scientific studies. However, not just temperature is changing along rural to urban gradients. We select the plants that are growing in our lawns and in cities, which can result in reduced genetic diversity and sometimes genetic bias in traits. For example, we might select a variety of tree that has a unique genetic signature that allows it to leaf out with a really beautiful red in the fall. However, my fixing that genetic trait, we might also be fixing others. We find that is true in the case of leaf out, where we have incidentally selected trees to plant in cities that leaf out later on average than other individuals of the same species. Thus, when we examine how temperature impacts spring leaf out timing using a gradient along a rural to urban gradient, we are ignoring that genetics are changing along this gradient too. When we account for this we find that trees are actually more sensitive to warming (ie. leaf out even earlier with warming springs) then we previously thought.

Featured Image

Photo by Natalia Gusakova on Unsplash

Photo by Natalia Gusakova on Unsplash

Why is it important?

Understanding when leaves come out in spring and fall off in autumn is critical to predicting the impacts of climate change. When leaves come out in spring, plants start to take up carbon dioxide, a greenhouse gas, from the atmosphere, they also start to transpire water, which cools the earth, and change the reflectivity of the planet which can also alter the heat balance of the globe. Thus knowing when leaf out happens each year and how much earlier it will continue to advance is critical for predicting how much the planet will continue to warm. The findings of this work could greatly improve the accuracy of our predictions and also indicates that urban plantings could benefit from higher genetic diversity.