The region is now at a "tipping point" as trees spread aggressively through high country, farmland and conservation areas, councillors have been warned.
These grizzly details were captured in an Environment Southland report presented to the council yesterday, which one elected member described as "sobering".
A species of concern was the Douglas fir for several reasons, including the distance its seed could travel, a tolerance to the climate and commercial popularity.
Its spread was accelerating at a rate which current investment and control could not keep up with, the report said.
"Without further intervention, vast areas of Northern Southland could be overtaken within 30 years, resulting in irreversible environmental and economic loss."
Productive land, native ecosystems and landscapes were all at risk, the report said.
It noted that Southland risked passing a "point of no return" under its current response.
• LDR is local body journalism co-funded by RNZ and NZ On Air.
