What you are failing to realize, is that due to any slender vertical object's orthogonal orientation to the earth, and the incredibly powerful magnetic molten core, the vertical objects amplify and channel gravitational forces, regardless of what material they are made of, be it wood, steel, or otherwise. The gravitational forces are particularly powerful when confronted with materials such as foam and balsa. While it is true that these materials are of quite low density, the particular gravitational energy associated with items protruding vertically from the surface of the earth is able to magnify the attraction of foam and balsa. At this point, even our most brilliant physicists have failed to truly explain this phenomenon. It's similar to two rare earth magnets in close proximity. At a certain distance, there is almost nothing you can do keep the foam and or balsa away from the vertically oriented object. This is a phenomenon I observed many times as a boy, flying RC planes. Until my first couple of flights with my Old Fogey, I had nearly forgotten about these anomalous attractive forces. I think it was about my third flight when I was quickly reminded! Fortunately, a little packing tape was able to fix the wing that contacted the light pole. With my nicer planes, not wanting to tempt fate, I try to stay as far as possible from any vertical objects protruding from the ground.
Also little known to nearly anyone but RC fliers is the hatred for RC planes that coniferous and deciduous trees posses. Many think of trees as more or less inanimate objects, but their malice for RC planes, combined with the above gravitational phenomenon, make them powerful enemies of RC fliers everywhere!!!