Sweet Pittosporum is a fast-growing tree that has become invasive in parts of Australia where it is not indigenous. The tree almost completely extinguishes the surrounding vegetation, but experts report that clearing the trees could allow this native vegetation to return.
In a new study from Monash University, scientists have investigated how clearing Pittosporum trees may affect birds such as the threatened Powerful Owl. The researchers found that the richness and abundance of birds is greatly reduced in areas with dense Pittosporum canopies.
“The almost complete absence of any understory vegetation and no ground cover means there is very little for birds to eat in invaded sites,” said study lead author Dr. Ben O’Leary.
“Most habitat components for birds exists within the Eucalyptus overstorey and mid canopy. The presence or removal of Pittosporum doesn’t appear to greatly influence ground storey bird species, which have been in long-term decline.”
The study also showed that there are also fewer carnivorous birds in sites that have been invaded by Pittosporum trees, which is likely due to the lack of vegetation and prey on the ground.
“While invaded sites are not great habitat, restoration projects need to ensure that the full range of habitats continue to be available during the transition period,” said Dr. O’Leary.
The removal of an invasive tree species without affecting other wildlife can be a challenge. In certain circumstances, the trees provide structural value to local flora and fauna.
“The trick is balancing the progression of weed control with the retention of enough structure to support local plants and animals,” said Dr. O’Leary.
Study co-author Ros Gleadow is a professor in the School of Biological Sciences who has been studying Pittosporum for over 40 years.
“It is important to get rid of the Pittosporum now,” said Professor Gleadow. “Not only does it suppress the understorey, but in all these years, I have never seen a eucalypt seedling growing under a Pittosporum canopy.”
“Once the old eucalypts at a site die, that’s it and it of both native vegetation and birds is impossible without major intervention.”
“For areas where Pittosporum is native, like around Sydney, management is philosophically complicated but there is no doubt that clearing will to help preserve biodiversity.”
The study is published in the journal Ecological Solutions and Evidence.