However , the retention of old stone walls , buildings and bridges can help to support its populations , even in cities .
As with most lichens , Physcia caesia is impacted by habitat loss through development , as well as by the trampling or overgrowth of its location .
The retention of old stone walls , buildings and bridges can help to support Physcia caesia 's populations , even in cities .
As with most lichens , Physcia caesia is impacted by habitat loss through development , as well as by the trampling or overgrowth of its location .