Both Labour's Sadiq Khan and the Conservatives' Zac Goldsmith have promised to ensure residents have access to green spaces, with Goldsmith, a lifelong environmentalist, also outlining extensive plans to make the city climate change-resilient through greening.
But Farrer said: "We can all agree with the candidates' call to make London a greener city but we need to see a commitment to real action to make landscape a central component of any future change.
"I would like to have seen a commitment to the management and stewardship of the landscape by ensuring revenue streams to allow the improvement of existing and new green spaces," he said.
"This could either be through greater funding for parks departments or better still, money and power for local communities to engage in the upkeep and improvement of local green spaces.
"Huge change is already happening to our physical city. London's story has always been one of change and we need a set of benchmark standards for green infrastructure that will bring about increased biodiversity, reduced air pollution, additional trees and safe movement and play so that they are binding for developers and the arbiters of change. Only through this we will deliver the housing and the liveable city we need."
Last week the London Assembly's environment committee warned the city's green spaces are at risk from the population increase.
Its report, ‘Growing, growing, gone: Long-term sustainable growth for London' (PDF), identifies the key challenges to accommodate the city's population growth. These include the severe pressure additional housing will put on green space and waterways, and the possibility that London's demand for water could outstrip supply by 20 per cent by 2040.
The assembly recommended an integrated water strategy across the areas of supply, demand, drainage and flood risk, and called for London to get more environmental benefit out of its green and blue infrastructure through multifunctional usage, such as enhancing drainage and biodiversity.
On 9 March the London Assembly’s environment committee challenged outgoing mayor Boris Johnson with his environmental record. It found while Johnson was elected in 2008 on the back of environmental pledges, not all of his environmental targets are due to be met (PDF). London’s carbon emissions, air pollution and waste record are particularly far off target.