Aaron this is an introduced member of the Agavaceae family Yucca filementosa a native of North America, it has probably survived dumping amongst garden waste. Its common name is Adams needle.
There seemed to be a lot of rubbish and weeds around this particular side of Mount Ainslie. Ideally should these Yuccas be removed, or are they fine just to leave growing there?
It should be removed but I have never seen them being invasive - I think they are an indicator of heavy past disturbance or an historic garden site (in this situation the plant may have cultural value)
It is also an indicator of past habitation where there are no longer remains of a property as these plants were often planted because of their resistance to drought- for example there are some near the Mount Mugga Mugga quarry where there was a house and also at the site of the Mount Domain property at Tidbinbilla.
How do you distinguish between Yucca filementosa and Yucca aloifolia (which is on the Census)? BTW the area is a previous landfill site (old Ainslie tip) and there were many garden plants when volunteers started work in 2008 including bamboo and pampas grass...
Oups that is another Yucca site, much further south of what I thought (which is on the transmission line easement part that runs through the old Ainslie tip landfill site) (should always check ...)