Following an investigation by the Press Association, it has been revealed that government funding for national parks has been cut by a quarter since 2011.
The current government has said it is committed to raising parks' budgets between now and 2020.
However, funding in 2020 will be as much as a fifth below 2010 levels, said the study, even before inflation is taken into account.
Among the parks affected were the Peak District, with annual funding cut from £8.3m to £6.3m, and the Lake District from £6.9m to £5.2m.
CLA Senior Rural Business and Economics Adviser Dr Charles Trotman said: “Our national parks in England and Wales are visited and enjoyed by millions of people and generate more than £4billion per year in visitor spend, a major contribution to the rural tourism economy.
“However, tourist information services in the parks have been badly affected by year-on-year budget cuts and the maintenance of these beloved landscapes through generations of careful land management also comes at a cost. Without vital tourism to keep the rural economy thriving, the future of our national parks is uncertain.
“Although Defra has pledged funding up to 2020, after this date it is unclear what will happen due to the loss of important European funding as a result of Brexit.
Dr Trotman concluded: “To guarantee the future of national parks it is crucial the Government acknowledges the major economic role they play in the overall economy and commits to support these precious landscapes without further budget cuts.”
