I reported to the land manager many times CNG in this area and suggested the reasons why it spreads:
1) a local resident mows the grass in the reserve behind his and his neighbour's backyards and then spreads the grass clippings along the drainage line; 2) and the area is a high traffic zone with dogs off lead, bike riding and walking (there is no official track).
I have been talking to perhaps 10 rangers over the past years since we started to work along the drainage line in 2004 proposing to draw up a management plan for the site.
CNG has spread rapidly, particularly in the past 2 LaNina years.