Campaigners are urging Prince William to invest in significant rewilding across swathes of Dartmoor’s predominantly farmed land.

The land became William’s after he inherited the Duchy of Cornwall, an extensive landholding including the largest privately owned area of Dartmoor national park, from his father, King Charles, when he succeeded to the throne.

Protesters chanted “Make it wild or make it ours” as they marched to South Hessary Tor on the moor on Saturday, before laying down a symbolic wicker gauntlet outside the offices of the duchy in Princetown, Devon.

If the Duke of Cornwall does not act, then the land, owned by the royals since 1337, should be returned to public ownership, biologist Emma Smart, the campaigns manager at grassroots group Wild Card, told the crowd. “Will he ignore us? Will he hear our demands? If he doesn’t, we’re going to take it.”

Hazel Draper, the communications coordinator at Wild Card, added: “Given his personal wealth and status, Prince William is in a position to show real leadership in this ecologically significant landscape and could inspire others to take action.”

Land campaigner Guy Shrubsole – who has previously described the Duchy as a “medieval anachronism” – said that most of Dartmoor is “devoid of trees and birds for miles”, with “too many sheep grazing for too much of the year” and destroying the habitats of other animals.

He said that remnants of temperate rainforest still cling to a few parts of the moor and should be nurtured back to greater prevalence, which could have far-reaching ecological benefits. “These ancient, gnarled wet woodlands, their branches carpeted with green mosses and festooned with rare lichens and fungi, are some of the most biodiverse habitats we have in Britain,” he added.

Peatland, which stores vast amounts of carbon, on the moor could also be far better cared for, since much has become degraded, according to Shrubsole. Natural England sources said earlier this year that none of the open moorland habitats in certain key areas of Dartmoor were in a favourable condition.

The protest follows controversy over the paying of £13m of taxpayer funds to tenant farmers on Dartmoor over the last decade to help restore it as a key national wildlife ecosystem, since the funding has led to scant improvement. Local Tory MPs have meanwhile warned that grazing limits could imperil some farm businesses.

A spokesperson for the Duchy of Cornwall said: “Sustainable stewardship is at the heart of everything the duchy does. We have championed the preservation of natural ecosystems for over 50 years and are constantly looking for new ways to continue improving biodiversity, conservation and public access to green spaces.”

In July, Prince William visited Wistman’s Wood, an ancient, nine-acre Dartmoor woodland that the duchy is working to double in size by 2040, while restoring 1,200 hectares (3,000 acres) of historically degraded peatland in the area by 2025. It is also working with partner organisations on the conservation of the red-listed curlew.

“We recognise that Prince William and the Duchy of Cornwall have made movements in the right direction on nature restoration and we congratulate them for this,” Draper added. “However what they are doing does not match the scale and pace of the climate and nature emergency that we are in.”