Infrastructure Malta will on Monday start emergency works in Valley Road that will include the pruning of 145 mature trees in Valley Road.
The road will be closed to traffic between 9pm and 5am every day until March 10.
The roads agency said the intervention will follow a detailed method statement as approved by regulatory authorities and discussions with stakeholders including local councils and residents.
It urged motorists to use an alternative route through Triq Fleur De Lys or Triq Dun Karm.
The tender for the works provides for the hard pruning of the trees' canopy by up to six metres. It also requires the removal of any low-hanging branches and those touching nearby buildings. Works will be overseen by an arborist, according to a nature permit issued by the Environment and Resources Authority.
Last week, Moviment Graffitti raised the alarm about the pruning of the trees, saying IM did not know the difference between pruning and butchery.
But on Monday it said most of its concerns have now been addressed, and it was satisfied that the works will be conducted with the necessary sensitivity.
In a statement, the NGO however added that what ultimately mattered was how the works were carried out. It urged the authorities to "limit interventions to what is strictly necessary".
In light of the approaching nesting period for birds, the group said that work should not be further postponed.
"Plans presented by Dr Charles F Grech, the arborist engaged by the contractor, are broadly satisfactory, and it is evident that efforts are being made to ensure that the works do not devolve into simple butchery of the 145 trees along the site."
While acknowledging that significant work is required to rectify years of neglect that have had a detrimental effect on the road, Moviment Graffitti said “these detrimental effects are the responsibility of the entities responsible for the management of the site”.
"Therefore, the corrections must be borne by the entities responsible and have as limited an impact on the trees and biodiversity they host as is possible.”
Moviment Graffitti expressed concern about "caveats", taking issue with the provision that all foliage within three metres of buildings will be pruned.
“This must be understood as a maximum and not as a general rule. Each tree or segment must be considered on a case-by-case basis and not simply cut in a straight line the entire length of the road.
"In many instances, pruning back by 1m or 1.5m is entirely sufficient to achieve the objectives of the project, in keeping with the principle that interventions are conducted in a sensitive manner.”
The group also noted that the Southern Nettle Tree (bagular) on site "should not be touched beyond what is absolutely necessary".
It also warned that the main branches should not be entirely cut down to the trunk: “This would likely destabilise the trees and constitute a hazard to pedestrian and vehicular traffic".