Last week, a neighbor knocked on our door. He was holding a twig covered with lichens. He wanted to know what heck they were and how could he get rid of them, because they were killing his tree. I explained that no, these were not killing his tree, but because the twigs were bare, their spores had germinated there to take advantage of the good light (without the leaves). He's not alone in thinking the the lichens are causing harm to trees, so I thought I should provide some needed background.