Security on One Tree Hill has been stepped up in the wake of a spate of illegal plantings on the Auckland landmark this week.

Auckland City Council arboriculture manager Mark Bowater said patrols, which usually inspected the summit several times day and night, had been increased in frequency.

Two pohutukawa and a swing ball set have been placed on the hilltop since the weekend, only to be removed by the council.

"Yesterday we just decided we needed to increase security patrols around the area, just to keep an eye on it," Mr Bowater said.

"This morning, it's all quiet, so it may be that we ease that back."

Mr Bowater said a major concern was possible damage to areas of archaeological importance.

"The summit site itself is an archeological site and it is of some significance," he said.

"It's fine for people to have a bit of fun, but we just need to be prudent that there's no damage in the process."

The first pohutukawa was planted by an unknown person, the second by broadcaster Paul Holmes, while the swingball set came from radio station ZM.

The hill has been without a tree since its iconic lone pine was removed in October 2000 after it had become unstable from two chainsaw attacks over the previous six years.

The council has an agreement with Ngati Whatua that replanting a replacement would be delayed until the tribe has settled treaty claims.

Mr Bowater said there had been other trees planted on the summit without resource consent before this week.

"There haven't been a large number, but it happens periodically, and the council has to remove them," he said.

"It's good that there seems to be a general acceptance that a tree like a pohutukawa would be quite acceptable, and pohutukawa form the basis of the council's replanting plan. It just a matter of doing the right way."

The council, which has resource consent, has nine trees -- six pohutukawa and three totara -- ready for replanting.

Planting a grove of trees is thought to be the best way of ensuring at least one survives in the summit's harsh conditions.