An organisation representing London’s longest nature trail fears its variety of species is under threat from a lack of investment and tree maintenance.

Friends of the Parkland Walk, which cares for the walkway stretching 4.5miles from Finsbury Park through Crouch End and Highgate to Muswell Hill, is concerned levels of flora, fauna and insects are plummeting because trees have been allowed to grow unchecked.

The group claims Haringey Council is failing to achieve targets set out in its own Parkland Walk Management Plan and is calling for more funding.

Some of the problems highlighted in the plan include cutting back invasive Japanese knotweed and maintaining bridges on the walk’s old railway lines.

Simon Olley, chairman of Friends of the Parkland Walk, says the issues are not being addressed.

Mr Olley, of St James’s Lane, Muswell Hill, said: “If allowed to continue, we can expect the Parkland Walk to become dominated by a number of highly successful [tree] species such as sycamore, holm oak, laurel and bramble and the range of flora will continue to diminish.

“This results in a poorer population of insects, butterflies and moths and this directly affects bird and other wildlife populations.”

The organisation is concerned that developments to the new Ashmount School building and the Cape Play and Youth Project have led to significant ecological damage to the embankment at Crouch Hill.

A large section of the nature trail falls under the responsibility of Haringey Council. But its parks budget was cut by £1.2million three years ago and Friends of the Parkland Walk says the council has been unable to commit to the vast majority of conservation recommendations for the trail.

The organisation has now appealed for help from City Hall.

The London Assembly’s environment committee has been carrying out a survey of London’s green spaces to assess their value for biodiversity.

Mr Olley said the only viable solution for “one of London’s greatest assets” is to receive more funding.

A spokesman for Haringey Council said: “We have worked closely with Friends of the Parkland Walk to agree a management plan for the nature reserve and win grants from the Forestry Commission, as well as funding regular conservation days with volunteers.

“We share the passion of the Friends in making the borough’s award-winning green spaces home to a diverse range of wildlife.”