Almost half a million pine tree seedlings have been turned to mulch, with National saying money and reputation have taken a hit after the destroyed seedlings were meant to go to the Government's One Billion Trees scheme.
It comes after 1.2 million seedlings were bought to plant in Northland, costing the taxpayer about $160,000.
Only 200,000 seedlings were planted due to the land being too wild, while 600,000 were re-distributed and 400,000 mulched.
The $32 million joint venture with the Ngati Hine Forestry Trust was to enable planting of pine and manukau over the next 20 years, with a projected return of $63 million.
National's Paul Goldsmith called the mulching "incompetence laid bare".
"Now we learn that the inaugural venture in the One Billion Trees scheme was a bust, with seedlings destroyed," he said.
"It shows the risks of wild and frenetic spending to an overtly political timetable."
Forestry Minister Shane Jones told Radio New Zealand he was "certainly not trivialising $160,000 for people all around New Zealand and particularly in the North".
"The officials will be giving an account of who did what and why it's turned out this way," he said. "Rest assured I'm not sweeping this under the carpet."