Tree and shrub weeds cause immense damage. As with all the other weed types they too can be toxic. Privet and Rhus cause asthma and severe allergic reactions.
African Olive, which takes over entire landscapes forming a monoculture (one species only), is now declared as ‘a process threatening to biodiversity’. Here it moves over an entire hillside at Mt Annan. It threatens much of the remaining original Cumberland Plan vegetation in the Sydney Basin.
Privet, Gleditsia, Box Elder – and many other tree weeds will also infest riparian zones. Long and sharp thorns on many tree and shrub weeds make removal extremely difficult. Blocking access to waterways they also destroy the beauty and biological health of creeklines and rivers.