Artificial light and trees

(Updated January 11, and January 16, 2015, and July 1, 2016)

Luciano Massetti, a colleague of mine from the Loss of the Night Network, recently took a series of photos in Florence that show trees near street lamps who's leaves still haven't fallen off:

LAN leaves 2 by Luciano Massetti is licensed under
a Creative Commons Attribution 4.0 International License.

LAN leaves 10 by Luciano Massetti is licensed under
a Creative Commons Attribution 4.0 International License.

LAN leaves 15 by Luciano Massetti is licensed under
a Creative Commons Attribution 4.0 International License.

LAN leaves 22 by Luciano Massetti is licensed under
a Creative Commons Attribution 4.0 International License.

LAN leaves 28 by Luciano Massetti is licensed under
a Creative Commons Attribution 4.0 International License.

At this year's Artificial Light at Night conference, Jonathan Bennie of Exeter University's Environmen and Sustainability Institute presented some intriguing data about a potential relationship between artificial light exposure and how early tree buds burst into leaves and how late leaves fall. His work, and related research by my IGB colleague Sibylle Schroer, isn't published yet, but it's starting to look like people's anecdotal observations that trees near street lamps behave differently isn't just a case of confirmation bias, it's a real phenomenon.

At this stage, there's very little information about which tree species are typically affected, or which types of lights have the strongest effect. Dr. Bennie is interested in pursuing this further, so if you've observed trees under lamps that are behaving differently than adjacent unlit trees, and if you are able to tell him the type of tree and type of lamp (e.g. high pressure sodium or LED), he'd like to hear from you. Photos of the effect are also useful, of course! You can find his contact information here.

If you liked this post, you might want to read the next one, which is about artificial light escaping from greenhouses at night. As always, if you have a photo related to artificial light that you'd like to share with the world, please send it to me along with your permission to publish it on the blog under a Creative Commons Attribution 4.0 International License as part of the "view from your app" photo series.

Update 1: @kylenano took these photos of a silver birch during the day and the night, so that you can see that it's the illuminated areas where the leaves are staying longer than they otherwise would.

Update 2: Stephen Rawlings took this time series of a brightly floodlit tree, showing how the leaves closest to the floodlight were the last to fall:

floodlit tree by Stephen Rawlings is licensed under
a Creative Commons Attribution 4.0 International License.

Update 3: A new paper shows that light is associated with a one week earlier budburst date in some species, and that this probably isn't an urban heat island effect (read it open access here). John Bennie has also published an open access paper about the potential effects of light on plants.