That's not the trees being cut down. The post indicates that the park service is planning to cut trees that have grown since the time of the battles. This doesn't effect what trees may have been there at the time of the War.
No park will cut down trees that were present during the battle unless they become a safety hazzard. The park historians at our Civil War battlefield parks are some of the most professional and conscientious people I have ever met. They have a deep sense of responsibility for the history of the parks and sacrifices that were made there.