The Libary of Congress has most of the Ft. Mahone original pictures and they may be accessed on line. I wouldn't put too much into a "sketch" of Ft. Mahone since artists may have put trees into the picture for scale. However, original pictures of the works in Petersburg will show a few trees inside forts. I think the picture of Ft. Steadman shows trees. Unfortunally access to Ft. Mahone by photographers was not possible until the fort was captured.