Conservative, Labour, Liberal Democrat and Green Party members used a London Wildlife Trust conference to hoist the environment up their agendas for the mayoral elections in May.
Conservative environment spokesman James Cleverley said mayor Boris Johnson had spent £6m improving parks, including a £2m overhaul of Burgess Park. He had planted almost 10,000 trees and launched a project to create 2,012 urban food-growing spaces.
But Green Party assembly member Jenny Jones said the mayor in fact chopped down 2,000 trees in Burgess Park, south London, and added that the 10,000-tree target was a "piffling" amount for a city the size of London.
Liberal Democrat Shas Sheehan said her party would prioritise air quality and the reduction of pesticides. She claimed that an initiative to cut pesticide use in one local authority backfired when grounds maintenance staff bought chemicals themselves.
Sheehan also opposed recent proposals backed by Johnson for a Thames Estuary airport.
Val Shawcross, who hopes to be deputy mayor under Labour's Ken Livingstone, said: "The Conservative record nationally is poor. We have seen a failed attempt to sell off England's forests and now we have plans for Boris Bonkers Airport on Thames Estuary."
She added: "Livingstone drew up a biodiversity action plan for London in 2002, a lot of which has been stripped out by the London Assembly during Johnson's control."