Heathland close to the M3 has been damaged in an overnight fire.
An estimated eight hectares (19 acres) of Chobham Common in Surrey was affected following reports of the fire at about 19:45 BST on Friday.
Off-road vehicles were used to reach the affected areas as almost 40 firefighters tackled flames. The fire service left the scene shortly after 08:00.
A further inspection will take place later, a spokeswoman said.
On Wednesday, 10 hectares (24 acres) of heathland on Ministry of Defence land at Ash Ranges, near Pirbright, Surrey, was affected by fire, alongside another incident at Chobham Common.
According to the Surrey Wildlife Trust, Chobham Common is the largest national nature reserve in the South East and "one of the finest remaining examples of lowland heath in the world".
On its website, the trust said: "Chobham Common is recognised as one of the best British sites for insects and spiders. It is the premier site for ladybirds, bees and wasps.
"It is the sheer range of habitats that provide this rare biodiversity. The expanses of heather are broken up by deep valley bogs, isolated pines and patches of grassland, gorse and silver birch."
Surrey Fire and Rescue tweeted on Thursday "the risk of heath fires remain high".