The cause of a gorse fire on the Mourne Mountains in Co Down is believed to have been deliberate, the Fire Service says.
It is estimated that 3.5 square kilometers of ground were affected by the blaze on Slieve Donard, which began in the early hours of Friday.
On Saturday the gorse fire was declared a major incident - and at its height, more than 100 firefighters from around Northern Ireland were involved in efforts to tackle the flames.
After three days of work, the fire was brought under control at around 4.50pm on Sunday.
“Calling an incident like this challenging doesn’t do justice to the effort our firefighters have put in over this weekend," said Chief Fire and Rescue Officer Michael Graham.
"The pictures we’ve seen on social media have shown us how hard they worked in intense conditions to extinguish this huge fire and prevent it spreading to threaten human life or property.
"While I am proud of the work our people did, we are all saddened by the destruction this fire has caused to our natural environment."
Michael Graham expressed his thanks "to our whole community to their support".
He went on: "I speak for every single firefighter and every single NIFRS employee when I say that we have been blown away by the outpouring of support we have seen.
"We have simply lost track of the number of people who contacted us offering anything they could to help us.
"We are proud to be an important part of such a generous and kind community."
Health Minister Robin Swann has thanked the emergency services involved in the response to the Mournes fire for all their work.
"The bravery, commitment and determination of these firefighters have very much shone through as they worked tirelessly in extreme circumstances to bring this fire under control," he said.
“These men and women are very much the heroes and protectors of our environment.
"But there is an onus on us all to take better care of our natural heritage and protect all the species that live there. Everyone has a role to play in protecting our landscape so future generations can enjoy and benefit from it."
Environment Minister Edwin Poots said the fire will have "caused untold damage to the biodiversity, wildlife and natural habitats of the area".
In a statement, the National Trust described it as a "tragedy" and said the area that was damaged will "take years to recover".
The charity said: "We are devastated to see the impact the fire has had on the fragile habitat of upper Slieve Donard.
"This Area of Outstanding Natural Beauty has been completely destroyed and will take years to recover.
"The heather landscape, which is a designated Special Area of Conservation, once alive with flora, fauna and diverse wildlife is now charred earth and ash."
They thanked the rescue organisations involved in brining the incident under control and asked anyone walking in the countryside to stick to paths and not to light fires.
"There is an urgent need for all agencies and bodies to work together with local communities to develop a long-term vision for the Mournes, looking at land use, visitor management, infrastructure management and coping with a changing climate," the statement went on.
"It is essential this is adequately resourced."
Meanwhile the Northern Ireland Fire and Rescue service urged people to be "extra fire aware at this time both in your home and in particular in the countryside".