Dr Phil Palmer hopes cattle won't be making a reappearance into the public Greendale Reserve, Otaihanga, anytime soon.
He said cattle had ventured into the reserve over Easter, likely from a stream on the seaward side, and caused damage.
Various native greenery such as carex geminatea, used to strengthen stream banks, ngaio, whitey wood, whau and toi toi had been chewed.
It wasn't easy to determine how many plants had been affected but "200 plants would be very conservative".
Parts of the Muaupoko Stream banks, which runs through the reserve, had been eroded by cattle climbing up or down.
Mr Palmer, who understood as many as five cows had been in the reserve, said damage to the stream banks was the main concern.
"The trees will grow again but the damage to the banks of the stream is much more difficult to repair.
"The only way is by using carex that has lots of roots that get into the soft sand and holds it.
"We have been working very hard to keep the intergrity of the banks."
Wire mesh, corrogated iron and bits of wood have been put across the stream, at the point where the reserve meets private property, by someone to try and stop cattle getting into the reserve.
Kāpiti Coast District Council parks and recreation manager Alison Law said, "We have spoken with the owner of the cows and will be working with him to make sure this can't happen again."
Mr Palmer, from Waikanae, said cattle in the reserve had been an ongoing issue.
The solution to the problem was "proper fencing".
Mr Palmer, who is in his 80s and spends one day a week working in the reserve, was one of the original people who helped create the reserve in the mid 1990s.
Throughout the years many people, including school children, have spent countless hours transforming the area into a thriving ecological environment.
Greendale Reserve, which covers 3.5ha, is a Forest and Bird environmental restoration project developed in partnership with Kāpiti Coast District Council supported by Greater Wellington Regional Council.