The good news...
Only the most degraded environments lose all their native plants.
Even a lone wattle can support insects, birds, fungi and even mammals.
In places that appear to be a waste of privet and lantana a few native trees and stunted seedlings of native plants may be waiting for you to rescue them.
If you remove the weeds in the root zone of the natives, they can take on new vigour and sow their seeds in the spaces from where the weeds were removed. That progress is incremental, with birds and butterflies progressively coming back. It's well worth the effort to control weeds!
Not so good...
Plants introduced from other continents are rarely food for native wildlife. Few native insects feed on introduced plants. As a result, such plants often grow out of control and become environmental weeds.
If the weeds take over, wildlife disappears in proportion. The 50 or so local butterflies need specific native plants to feed on. Without them, the butterflies and many other specialised insects just disappear.
As an example, see this before and after weeding photo.
Some of the weeds that we control are:
privet(s) & camphor laurel (introduced from China)
tradescantia (from S. America)
non-native grasses (from the Americas, Europe & Africa)
blackberry (from Europe)
Brazilian fireweed (from S. America)
lantana (from S. America)
thistles (from Europe)
If you need to identify a weed, try this useful site