Through his long life Havaas collected a large number of plants, mainly mosses and lichens. The Bergen Museum received 23,000 contributions from him. With respect to the rare, small species of lichen, Granvin is probably among the best studied areas in the world, thanks to Havaas. Especially Nesheimshorgi proved to be an interesting locality, among other reasons for being home to a species of lichen that was new to science when it was discovered here.
Havaas published a lot. His main work was Lichenes Norwegiae occidentalis exsiccati, which the Bergen museum began to distribute in 1912. 25 sets were distributed among museums and scientists around the world. This made his name famous. One can see parts of his collections in the village square in Granvin Centre.
