Scott Saddler, executive branch manager for the National Arboretum Canberra and Stromlo Forest Park, has resigned after almost a decade of guiding both sites to becoming world-class facilities.
Mr Saddler, 60, said his resignation took effect on March 26.
He has been head of the arboretum for nine and a half years, almost its entire life, with the site turning 11 this year.
"When I got there, there were 44,000 sticks in the ground. Now there are 44,00 trees that are flourishing," Mr Saddler said.
Mr Saddler said he had "a couple of things up his sleeve" regarding his next move, but he did not yet want to reveal them. He did plan to stay in Canberra.
John Mackay, former chair and current patron of the arboretum, praised Mr Saddler's stewardship of the 250-hectare site, which features more than 44,000 rare and endangered trees.
"In nine and a half years, he's increased patronage to more than a million people a year and developed the arboretum into a world-class facility," Mr Mackay said.
Mr Saddler said managing the arboretum, with trees from more than 100 countries growing in 94 forests, had not been easy.
"I say having 100 forests is like having 100 children," Mr Saddler said.
"They all want something different to eat. Some want a lot to drink, others want a little.
"The learning curve has been exceptional."
Mr Saddler's background is in horticulture and parks management, working in local government from Townsville to Wagga Wagga to Sydney and also running his own landscaping business in London.
Since starting in his role at the arboretum almost a decade ago, he has worked to include art as well as trees in the facility.
Last year, he announced the commissioning of a Forest Sculpture Gallery work for the front dam to commemorate the first 10 years of the arboretum.
Mr Saddler paid tribute to his staff, saying there were eight in his area when he started, while there were now 37.
"We've been severely understaffed for a number of years," he said.
"If you look at the Botanic Gardens in Sydney, they have 312 staff and it's roughly the same size.
"That's where the hard yards had to be put in - constantly asking staff to do more and more."
Mr Saddler said a highlight for him was the 10th birthday celebrations for the arboretum last year and the 71 trees planted over the years by dignitaries.
He thanked former chief minister Jon Stanhope for having the vision to turn a weed-filled paddock into a museum of trees.
"I often say it was because of his doggedness we have this world-class facility," Mr Saddler said.
The ACT Government has been asked who Mr Saddler's replacement will be, with a response to come.
