Georges River Council mayor Kevin Green said thieves have acted selfishly after stealing plants following a Spark your Park event from Charles Street Reserve at Oatley.
Councillor Greene said the whole community suffers as a result of the theft.
"We have been bowled over by the enthusiasm of local community members who volunteered their time and energy to help green up their local parks, so it's bitterly disappointing to see plants stolen and their hard work undone," Councillor Greene said.
"There were 24 newly planted shrubs stolen from our previous event at Empress Reserve in Hurstville in September, and now eight callistemons have been taken from Charles Street Reserve in Oatley.
"I would like to remind the thieves that these plants are intended for everyone to enjoy. The whole idea behind Spark your Park is to create public spaces that the whole community has the opportunity to enjoy.
"It's also worth pointing out that this kind of theft is a crime, and will be treated as such should the thieves be caught.
"Parks have become increasingly important and appreciated during the COVID-19 pandemic. We know that nature plays a vital role in our wellbeing - being able to enjoy greenspace is even linked to better health, including lower blood pressure and cardiovascular disease as well as improved mental health.
"Please don't put your wants above the wellbeing of your community members. That's not the kind of community we want. As a council we are working to beautify and green up our community parks and gardens, and we would appreciate the cooperation and support of everyone in helping us achieve this," Cr Greene said.
