The National Capital Authority will embark on a wide-ranging annual planting program to increase, diversify and rejuvenate trees on national land over the coming decade.
A new tree management policy commits the authority to increasing tree canopy cover on land it controls to 40 per cent by 2030, up from 33 per cent.
National Capital Authority chief executive Sally Barnes said the approach to tree management needed to be adventurous again.
"We have to be able to say to the community, 'Come with us. Some of this'll work, some of this might not work, but we need to be adventurous'. We need to try different things in different places; prepare to fail if we have to, but if we're learning, all the better," Ms Barnes said.
The authority, which manages 18,000 trees, will work to increase the number of juvenile trees and have a wider spread of tree species, all while maintaining the heritage values of Canberra's plantings.
New non-invasive species will be trialled at the Linsday Pryor National Arboretum to test whether they are suited to Canberra's climate, in work that harks back to the early experiments carried out by afforestation officer Charles Weston.
Ms Barnes said instead of the usual replacement approach, the authority would now look for areas where trees could be added.
National Capital Authority chief planner Andrew Smith said it was important to diversify the types of trees to make sure the population was resilient if faced with disease or new pest.
"The landscape characteristic of the city will go and it'll go very slowly and then it'll go quickly, and all of a sudden there'll be nothing. We've got to start now, that big renewal project," Mr Smith said.
"It's going to have to be in big steps and we're going to have to take bold moves."
The policy sets a target of making sure 10 per cent of trees managed by the authority are juvenile, up from 8 per cent.
"Urban trees are some of Canberra's most valuable assets and must therefore be protected, maintained and replaced to enhance their collective heritage, environmental, social and economic values," the policy said.
A 2019 audit of the authority's trees found 70 per cent would need to be replaced within the next 40 years.
While 93 per cent of the authority's trees have a useful life expectancy of over 20 years, just 23 per cent have a life expectancy above 40 years.
The management policy says the authority will replace trees with the same species, except where those trees are no longer viable. In those cases, a different species that "contributes to the same heritage value" will be planted.
"As custodians of this living place there is a need to ensure a dynamic and healthy urban forest while acknowledging and respecting the heritage values of the landscape," the policy said.
"It will be most important in managing the treescape in changing environmental conditions to consider different tree species that will thrive in order to safeguard the urban forest for future generations."
The plan noted the commitment to diversifying the age and type of trees on land controlled by National Capital Authority would create a more resilient tree population.
"Climate change, urban development and the need for open space to be multi-functional all place various stresses on our trees and in some cases could cause an increase in the number of trees that decline and die," the plan said.
The plan commits the authority to ensuring no one tree type makes up more than 10 per cent of the total tree population.
Eucalyptus mannifera currently makes up 12 per cent of the population, while Eucalyptus bicostata makes up 11.5 per cent.
The management plan noted trees are one of the most efficient and cost-effective methods for helping Canberra's climate change adaptation.
"[Trees] also provide habitat and food for wildlife, reduce energy consumption in buildings and well managed, safe, green areas can encourage people to walk or ride rather than drive," the plan said.
"The [National Capital Authority] considers its trees an important asset, therefore all management options will be explored before tree removal is recommended. While tree removal is a last resort management option, public safety always takes priority."
Assistant Minister for Regional Development and Territory Nola Marino said it was timely to plan for Canberra's future as the city's trees aged.
"It's a time to reflect on the past, but also infuse contemporary thinking and practices to create a blueprint to ensure the urban forest is resilient and thriving in the future, particularly in the face of a changing climate," Mrs Marino said.
The ACT government's urban forest strategy, released earlier this year, commits the entire city to having 30 per cent tree canopy cover in the next 25 years.
Canberra currently has 19 per cent tree canopy cover, with coverage in some suburbs above 40 per cent and below 5 per cent in others.
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