Chainsaws are set to roar into action on Thursday when the felling of about 50 trees begins along stretches of Anzac Parade and Alison Road to make way for the $2.1 billion light rail line connecting Randwick and Kensington with Sydney's CBD. Trees along the two major roadways will also be pruned for the project.

In a last-ditch effort to save the trees, residents, environmental groups and politicians will hold a rally near Randwick Racecourse at 10am on Wednesday.

Centennial Park Residents Association co-chair Peter Tzannes said the trees – some as old as 100 years – could easily be saved if the government allowed for an alternative route for the light rail line.

"There is a better way of doing this without the destruction of mature trees. These trees are so majestic," said Mr Tzannes, who has lived near the park since 1951. "Centennial Park is one of our few real jewels in the city. It is going to be devastating ... and something has to be done to stop this cowboy approach."

Shortly before new year, contractors felled about 13 trees at the intersection of Alison and Wansey roads, and 10 trees beside the Eastern Distributor at Moore Park.

The trees now facing the axe along Alison Road are located between Anzac Parade and Darley Road. ALTRAC, the consortium building the light rail line, has approval to remove or prune the trees between January 7 and 16. Most of the trees are native fig.

Randwick City Council has led a campaign in recent weeks to save the trees, and erected about 80 signs around those that are likely to face the chainsaws.

Calling on the government to delay the removal, Randwick councillor Murray Matson said the trees could be saved by shifting the light rail line back to the south side of Alison Road, beside the racecourse.

A spokeswoman for Transport for NSW said the final number of trees to be felled would depend on a range of assessments, including nearby utilities, and an arborist would assess each tree.

"The goal is to retain as many trees as possible throughout the design and construction of the project. Many more trees will be planted than are removed," she said.

Transport for NSW has guaranteed that any tree removed will be replaced with at least two new trees, while it will replace those deemed significant with eight new ones.

The Labor MP for Kingsford-Smith, Matt Thistlethwaite, said the trees could be saved and the light rail line maintained if the Baird government was willing to entertain alternatives.

"This is the iconic green curtain bequeathed to the people a century ago and destroyed by cost blowouts and mismanagement of the light rail project," he said.

Meanwhile, the University of NSW has raised concerns that passenger volumes at light-rail stops on Anzac Parade and High Street will be much higher than the government's forecasts.

"Although additional services may be provided to cater for the additional growth in patronage over time, the size of the stops have not been designed to cater for this expected growth," it said in a submission on the latest changes to the light rail project.

Aside from catering to staff and students, the university said residents from surrounding areas would increase crowding at the stops.

About 26,000 people a day caught public transport to the university in 2014, a near 11 per cent increase since 2007. The university predicts about 21,000 staff and students to use the light rail line by 2021. The entire route for the line from Circular Quay to Kensington and Randwick is 12 kilometres.