Whakahekerau — Second Beach ecology action group took part in a community planting day at St Clair last Sunday.
Convener Steve King said about 120 indigenous trees and shrubs were planted at the former quarry at Second Beach.
However, when he visited the site late in the afternoon on Sunday he was disappointed to see about nine plants had been pulled out and thrown around, Mr King said.
"There was no indication who did it."
The volunteer group was formed online during the Covid-19 lockdown last year and had an agreement with the Dunedin City Council to provide weeding, planting and pest control at the site, he said.
The council provided the plants, which were sourced from specialist native plant growers Ribbonwood Nurseries.
The former quarry was being regenerated with plants suitable for the area and about 20 volunteers took time out to weed and place the plants last weekend.
"We wanted to add to the diversity to attract more native birds."
Also helping bring back birdlife was a programme of trapping pests being undertaken by the group, Mr King said.
At his last count about 21 possums and three rats had been captured.