The National Trust has entered the battle against further development at Stansted Airport.
The inquiry continues into the expansion plans
The trust is telling a public inquiry that increased aircraft traffic would change the "special nature" of Hatfield Forest, which borders Herts and Essex.
It described the site as one of the few remaining medieval royal hunting forests in Europe.
BAA wants to increase the number of flights leaving Stansted from 241,000 to 264,000 a year.
"The trust has consistently opposed the expansion of Stansted Airport and its impact on Hatfield Forest - a unique medieval hunting forest home to nearly 1,000 ancient trees and visited by more than 150,000 people each year," a trust spokesman said.
"Evidence recently collated by the National Trust has revealed worrying information about the potential impact of increased noise on Hatfield Forest, if the proposed expansion of Stansted airport goes ahead.
"Periods of tranquillity between planes taking off and landing on an average summer day would drop from 117 seconds to 81 seconds."
The National Trust believes higher airport traffic levels could reduce visitor numbers.
The spokesman said a number of differrent species could be found in the woods - 614 fungi, 648 beetles - of which 92 were scarce or rare - 484 moths, 104 lichens, 65 breeding birds, 26 mammals and eight bats.
BAA argues that expansion is essential to the economy and in line with government policy.
The plans have attracted widespread opposition from locals.