Fern on log

The log referred to in this post is the remains of a piquiá tree (Caryocar villosum) that is said to have fallen more than 50 years ago, long before my time. Neighbors say that the log used to be almost on top of the road going through what is now Bosque Santa Lúcia. Road construction equipment eventually pushed it to the side, where it remains to this day. For the most part, it's hollow inside. I'm told that the heart wood was removed but I wonder how this was done without destroying most of the outer log, which is also harder than a rock. In the past I've tried filling the hollow spaces with dead wood from other trees, as well as some dirt, hoping to use it as a giant planter. Within a year or so all that material decomposes and the hollowness remains. This past winter, Áurea planted some lilies on top of the log and they're doing well. Now it's summer time, our dry season, so they need to be watered every day. The wild fern in the attached image was a leftover from the rainy season and it would normally die back this time of the year, but I've watered it on a regular basis, as I need to water the lilies.