A tree planting program will struggle to achieve a 30 per cent canopy cover over Canberra in the next two decades because sapling supplies and staff are limited, an audit has warned.
The government also does not have a strategic plan for replacing mature trees, despite modelling showing more than 200,000 trees in Canberra will be dead by 2045 and posed a risk to the 30 per cent canopy target.
The audit said the government should prioritise its plan to commission a report on suburbs at risk of losing canopy cover due to ageing trees and employ a senior arborist tasked with planning for the replacement of mature trees.
The ACT government fell short of its target of planting 18,000 trees in 2022-23 - just 12,650 were planted - and has wound back targets for future years, in some cases by as much as half.
"Without appropriate planning, or other mitigation strategies, to make up this shortfall in future years and address the ongoing risks and challenges to the planting program, the reduction in planting targets will have an impact on the goal to plant 459,000 trees and achieve 30 per cent canopy cover by 2045," the audit said.
The Auditor-General's office assessed the Transport Canberra and City Services Directorate's urban tree management, which is part of the ACT government's plan to achieve a 30 per cent tree canopy cover over Canberra by 2045.
The audit, published on Friday, made 11 recommendations, including a review of the preferred species list, a new agreement with Yarralumla Nursery and the creation of a strategic replacement program focused on identifying and replacing at-risk mature trees.
The government's urban forest strategy identified the need for more than 450,000 trees to be planted on urban public land, but the directorate considers that number to be "an informed estimate", the audit said.
"TCCS otherwise estimated that this equates to around 20,000 trees that would need to be planted annually for the next 25 years," the audit said.
"TCCS has identified that this will be difficult to achieve and will require a significant and long-term investment in additional staffing resources, equipment and infrastructure."
The directorate has increased the number of trees it plans to plant annually, but the audit warned of significant challenges posed by limited in-house and contractor resourcing, and tree stock supply.
"Managing community expectations for the planting of trees is also a challenge for TCCS. Approximately 12.4 per cent of all tree plantings since spring 2021 (2485 trees) have been the subject of a re-route process," the audit said.
"Re-routes describe the process for when a tree cannot be planted due to accessibility issues or conflict with other services or other preventative planting issues arise at the time of planting.
"Re-routes are mostly caused by members of the community opposing the planting of a tree. Significant time and effort is required by TCCS to manage and minimise the risk of re-routes."
The directorate planted 28,809 trees between 2020-21 and 2022-23.
"Planting targets for 2020-21 and 2021-22 were achieved (6000 and 10,000 respectively) but the planting target of 18,000 trees in 2022-23 was not achieved," the audit said.
The audit also warned the quality of tree data kept by the directorate was a challenge, finding it may be affected by poor record keeping. The audit recommended reporting on plantings in suburbs with low tree canopy cover or that are vulnerable to heat.
"TCCS should improve its public reporting on tree planting numbers and achievement against the canopy cover target by including data on tree survival rates and cumulative planting numbers in suburbs with low canopy coverage that are vulnerable to urban heat," the audit recommended.
