When I first moved to Stockholm, July 2013 to be exact, I enjoyed the city to its fullest. There seemed to be an endless supply of sun, and with all its water, hills and colourful houses, I sometimes felt like being in the Mediterranean. I walked through the city for hours, and once I got tired I looked for a nice place to take a nap. Under a large tree that provided just the right amount of shades, I found just the right spot.
But what was that?! Some sticky substance was laying right where I had planned to rest. It was dripping down from the trees. All of a sudden I noticed it everywhere. Walking over Kungsträdgården (a central square) my flip flops seemed almost glued to the pavement. The saddle and handles of my bicycle were sticky too. Why would anyone plant trees like these in an urban environment? I knew not all trees drip like this.
The autumn came and I forgot about the problem, but now, with the new spring, the sticky stuff is back again. Then I met Erik Käll, during the UBC seminar I wrote about last week, who is a biologist working for Örebro municipality. Then I remembered the sticky stuff, and I asked him what it is.
The stuff dripping from trees is called honeydew, and unlike many people think, it is not resin. These are plant lice that suck sap out of leaves. These lice suck out much more sap than they need, the surplus they excrete forms the sticky goo that we know as honeydew. In other words, it’s lice poo.
Some trees, like the Linden trees, attract more lice than other trees, which means that they also drip more than other trees. So really, it is not necessary to have trees in the city that cause this kind of problem. When planning green in cities it is important to consider what problems or benefits might arise from them, since they will be around for quite some time. That’s also why it’s so important this is done by people with the right expertise.
During the summer I will interview Erik Käll to discuss in detail what to think about when planning green in cities. If you have any questions about the subject, leave a comment, and i will discuss it with him.