Firefighters discovered three blazes at the gardens. Credit:Ken Irwin The William Tell Pavilion, rebuilt in 1997 after being destroyed in an accidental fire in 1994, was razed to the ground. ''I'm devastated again,'' Dr Entwisle said. ''It's horrible to walk into the gardens this morning and smell the smoke and just see the ash where we had these wonderful shelters. ''The William Tell shelter is one that people would picnic in. Our harpist would play in it, on the lake. It was a beautiful shelter.

Firefighters had a difficult time getting water into the gardens to extinguish the fires. Credit:Ken Irwin ''Interestingly it was rebuilt ... after a fire, and we tried to create the original design. ''The other building that burnt was a new toilet block built on the lakeside. ''The third shelter was an older style heritage shelter which was nestled in above The Terrace cafe. ''I suspect it needs a complete rebuilding as well.

''It dates back to the early times of the gardens, it'd be about a century old. It's one of the older-style shelters of which there's probably a handful of them around.'' Last July, vandals damaged several trees with an axe or machete, including one of the state's most significant trees, the Separation Tree. It was the second time the 400-year-old river red gum had been ringbarked. Six weeks before the trees were attacked, intruders entered the Arid Garden and slashed 80 per cent of the tall column-like cacti. Dr Entwisle said it was distressing to have so many vandalism attacks, which had prompted increased patrols and the installation of security cameras and a fence around the Separation Tree. He said short of installing razor wire around the fence it was impossible to protect the 36 hectare site.

''It's such a hard thing: we want people to get close to the plants so we don't want to do anything to deter that, but we need to provide some protection,'' he said. MFB spokesman Trevor Woodward said it had been difficult for firefighters to get water to the burning pavilions because they were so far inside the gardens. "Obviously, our trucks don't want to trample all over the lawns and what not, plus the fact that they'd probably get bogged down if they did,'' he said. He said about 20 firefighters worked to extinguish the blazes. Mr Woodward said setting fire to the log cabin-type structures would have taken a concerted effort.

"These people were determined. They didn't do it once, they did it three times. "It's disappointing that someone or some people have taken to lighting these pavilions up. "I mean, it's very disappointing for people who use the park quite regularly." Detectives from the Melbourne crime investigation are investigating. Detective Senior Constable Megan Macinnes said police would examine CCTV footage.

''Patrols were conducted this morning and also a complete search of the gardens was undertaken. ''Obviously, it’s very disappointing and it’s difficult to establish what possible motive there could be at this stage, so it’s very disappointing and it’s possibly a pointless crime.'' She said the value of the damage was yet to be determined. Anyone with information is urged to call Crime Stoppers on 1800 333 000.