Deer have been identified as the biggest single threat to native woodland.
An eight-year study carried out by Forestry Commission Scotland has blamed overgrazing for a “significant” loss of ancient trees in the last 40 years.
Conservationists called on landowners to prevent the animals’ spread, but the Association of Deer Management Groups insisted other factors had to be taken into account. Unveiling the study, described as the most comprehensive of its kind, Environment Minister Paul Wheelhouse said 22.5% of Scottish forests were native woodlands and 42% were in the Highlands.
“While we have no comparable historic data to compare with the survey, the survey findings suggest that over the past 40 years we have lost a significant amount of ancient woodland in the uplands,” he said.
“The survey has shown that the most widespread threat to native woodland health and regeneration is excessive browsing and grazing, mainly by deer.”
The Scottish Wildlife Trust urged landowners and managers to support sustainable deer management and stick to the voluntary code of practice in order to reduce the damage of overgrazing.
The charity’s head of policy Maggie Keegan said: “We know that in some areas of Scotland, deer numbers are too high and are out of kilter with the natural environment.
“This comprehensive, eight-year, study provides compelling evidence that cannot be ignored – deer in some areas of the uplands are the number-one threat to Scotland’s ancient native woodlands.”
Carol Evans, director of the Woodland Trust Scotland said: “We have real concerns about the level of damage from grazing that has been identified.”
Richard Cooke, chairman of the Association of Deer Management Groups, said the study would be “extremely helpful” for focusing attention on areas where there are specific issues concerning deer and native woodlands.
“We do believe however that there has been a significant turnaround in the last 30 years in the impacts of deer on native woodland and it is too easy to blame deer at every turn when other factors, for example grazing from other herbivores and now widespread tree disease, are also taking their toll,” he added.
Robin-Leslie Melville, a north-east based independent land agent, said Mr Cooke’s association deserved praise for achieving “a huge amount” in the last 30 years.
“Aspects such as deer fencing, culling and a general decline in numbers have been effective in dealing with the issue,” he said.