Green spaces will be lost forever if developers are allowed to build on them, campaigners have warned.
House builders PMG Limited and Persimmon Homes want to build a 618-home development on the site of Gwern y Domen in Rudry.
The plans are being opposed by the Gwern y Domen Conservation Group, which was set up to protect the area stretching from Rudry to Caerphilly town.
The group has been backed in their fight by TV wildlife presenter Iolo Williams who has described the area as “unique”.
Developers have said the project will provide much-needed homes and jobs for the area.
Meanwhile, Persimmon has also begun a pre-application consultation on a proposed 300-home development at Grove Park in Blackwood.
The planning application for Gwern y Domen has recently been submitted to Caerphilly County Borough Council.
The Gwern y Domen Conservation Group has vowed to fight the proposal and has been backed by TV presenter Iolo Williams.
Speaking on a recent visit to the area, he said: “I’m here to support the Gwern y Domen Conservation Group because this land here is so valuable from a wildlife point of view.
“You’ve got barn owls, great crested newts, long-eared bats, lesser horseshoe bats, you’ve got wax-capped fungi here.
“The combination of all of this wildlife, you just don’t see anymore in Wales. When I drive around Wales all I see are green deserts – rye grass.
“I don’t see places like this because they’ve all been ploughed up and re-seeded, sprayed, ‘improved’, this hasn’t been touched – or hardly been touched – from a fertilizer and pesticide point of view for probably over 100 years. That makes it pretty unique.
“On top of the value for wildlife, you’ve got to think about people. You’ve got Caerphilly and Rudry right on the doorstep. If this is built on, where are they going to go? Where are they going to go for their walks? Where are they going to go with their dogs? Where are they going to go with their kids?”
He added: “We undervalue the use of these places for people for their mental health. It is vital that we fight this. This is being done for greed – it’s not a necessity, this is greed pure and simple.”
Jayne Garland, Chair of the Gwern y Domen Conservation Group, said: “We know that Wales needs houses, but the type of housing Wales needs is social housing. In terms of Caerphilly, it doesn’t need the houses that are being proposed here.
“The numbers they have come up with were grossly over calculated. Caerphilly basin itself is on target for that housing need, so we do not need houses in Caerphilly basin at all.
“This is purely and simply for a national developer’s profit line and nothing to do with community.
“The community here do not want large family-sized houses for people who are travelling from Bristol, Cardiff and Newport to come and live on the side of a beautiful mountainside at the cost of community benefit.”
The group played a major part in campaigning to get Caerphilly County Borough Council’s draft Local Development Plan withdrawn – which had earmarked Gwern y Domen and the Grove Park site for housing developments.
Despite the council formally withdrawing the draft LDP, developers have decided to proceed.
The reasoning is that Caerphilly’s currently adopted LDP – a planning blueprint for developers – is out of date because it does not set out a clear housing supply plan for the next five years.
The lack of an up-to-date LDP has allowed several developments to be approved on appeal, such as a 300-home plan in Pandy Road in Bedwas.
The council is currently working with other local councils across South Wales to draw up a regional development plan.
Blackwood councillor Nigel Dix however has questioned whether Caerphilly County Borough Council is doing enough to attract developers to build on brownfield sites – land that has already been used.
He said: “The council has a duty to protect our green spaces, because once they are gone, they are gone.”
Cllr Dix, who is an independent councillor, also said the council should be doing more to market and sell its own brownfield sites, such as the offices in Pontllanfraith and the sites of Oakdale and Pontllanfraith schools when they become disused.
He said: “By not bringing these properties to market in a business-like manner, they are leaving our fields exposed to development.”
A spokesman for Caerphilly County Borough said: “The council has a valid LDP in place, however, we don’t currently have a five- year housing land supply.
“This was one of the main reasons for the review of the current LDP, which the council agreed to defer pending the development of a regional Strategic Development Plan.
“These discussions are currently ongoing via the Cardiff Capital Region. The council considers each application received via the planning committee and one of the factors considered is the need for housing to meet the five-year housing land supply.
“A number of applications have been considered by the committee which, following their refusal, Welsh Government then overturned at appeal.”
The spokesman added that the council has marketed some of their sites, including the former council offices at Pontllanfraith, which has had a positive response from the market.
A spokesman for Persimmon Homes said the two proposed developments were supported by “robust evidence” which address their potential impact.
They will also provide hundreds of construction jobs.
He said: “The council’s LDP has failed to deliver the necessary housing land supply since it was adopted in November 2010.
“This has been acknowledged by the council in the consecutive Annual Monitoring Reports.
“The Joint Housing Land Availability Study 2016 concludes that the council has only a 1.5 year housing land supply as opposed to the required five-year housing land supply specified in Welsh Government policy.
“The withdrawal of the Deposit Draft Replacement LDP in 2016 means that there are no plans to address the housing land supply. The submission of a planning application is the only way which the development industry can start to address the acute housing shortage in Caerphilly.”