Camphor Laurels
These trees were introduced to Australia a long time ago. They were ideal for planting around schools - lovely shade and no maintenance. Many are still there. Their crushed leaves have a lovely camphor smell and the timber is very decorative.
However they have become one of the country's worst weeds. Their prolific seeds are spread by birds and the tree now dominates most unmanaged waterways in SE Queensland and northern NSW - to the exclusion of most other native plant species.
Their method of domination is not to just shade out the competition. The trees are also reputed to exude chemicals which are antagonistic to other plant growth, possibly by contamination of the water.
Anecdotally, every part of this species is poisonous to fauna. In short these toxic pests are an environmental scourge.
So I recently found myself in the ambivalent position of having to save two of these trees because of construction activities. Their claim to fame was that they are heritage listed and must be retained even though a large section of their structural roots were to be removed.
There are many trees that deserve heritage listing. A known weed pest is not one of them.