Vandals torched a bench in Friarwood Valley Gardens during the weekend.
The bench, which was funded by volunteer group Friends of Friarwood Valley Gardens, was installed in 2017.
The group estimate that it will cost at least £600 to replace it.
Rachel Riley, who volunteers with the Friends, said: “It’s just soul destroying.
“We can’t do anything nice without some idiots ruining it.
“It was the latest picnic bench, which cost over £1,000 to install.
“The bench itself is about £600, but there was the base and installation fee too.
“The first I heard of it was on Sunday morning.
“I went down and had a look around but obviously this fire had been and gone.
“Who’s even thinking ‘let’s set fire to the picnic bench today?’
“The worrying thing for us now is that summer’s coming, and the long evenings attract more people.
“The Valley Gardens people are all volunteers and we do everything we can to help.
“That money was raised by us and now it’s just gone up in flames.”
It is the latest in a string of vandalism attacks at the park, with vandals pulling down trees, burning bins and destroying the park’s stage in recent months.
The Friends group thanked the public for their support following all the attacks.
Rachel said: “These things happen and they always do. It does get the community backing us up, but the thing is the gardens have been looking lovely at the moment.
“We did a litter pick there recently. It’s lovely and we’ve got a fairy garden area for families.
“We’ve got some big events planned this year.”
The Friends are not holding a fundraiser to help fund a replacement bench, but donations to the group are welcome.
To contact the Friends, search Facebook for Friends of Friarwood Valley Gardens, Pontefract.
It is thought the fire was started between 9pm on Saturday, April 6, and 9am the next morning.
Anyone with any information on the fire is asked to contact West Yorkshire Police on 101, quoting crime reference number 13190179164.
Information can also be given anonymously to CrimeStoppers on 0800 555 111.