Bird community recovery following invasive tree removal

Invasive plants can lead to significant changes in the abundance and
diversity of the existing flora. Restoration programs, therefore, largely
focus on the recovery of the vegetation. Faunal responses have received
less attention. Here we examined whether or not bird communities recovered
following removal of a native, invasive tree in South Eastern
Australia with a view to evaluating whether this could be used as
a tool for assessing the effectiveness of the remediation programs.
Pittosporum undulatum is an Australian native tree that has become highly
invasive in areas well outside its original range within Australia and in
many other regions of the world. In the Azores, for example, it is
associated with changes in bird communities. In Australia, high density P.
undulatum is the cause of major declines in biodiversity of flora and the
total suppression of regeneration of Eucalyptus. Its removal from nature
reserves across temperate south eastern Australia has been effective in
allowing many plant communities to recover, but the impact on birds is
unknown. We compared the species richness, density and functionality of
local resident bird communities across original remnant vegetation and
invaded areas with those that had been cleared of invasive P. undulatum
populations at different times. Areas infested with P. undulatum had fewer
carnivorous birds but overall there did not appear to be any strong
influence on species richness, or density. However, when invaded areas
were examined at a finer scale by partitioning the observations into
‘above’ or ‘within’ and ‘below’ the dense P. undulatum canopy, strong
differences were detected with fewer birds and fewer species relative to
the diversity and abundance of birds in the Eucalyptus overstory. Our work
demonstrates that while P. undulatum provides habitat for birds, there is
a difference in the relative proportions of different functional groups.
This is important, particularly in light of the long-term decline in
ground dwelling bird communities across the temperate regions of the
continent. We conclude that birds are a useful bioindicator of habitat
health and that the inclusion of avian monitoring programs could improve
the evaluation of the efficacy of restoration projects.