A little on Ayer Itam Forest Reserve's wartime history:

Wartime Historical Legacy

World War II has left an indelible mark on the history of this forest which was used as a bombing target of the Japanese air force during WWII. According to information obtained from the Orang Asli, there could still be unexploded live bombs throughout the forest. One of them was discovered after Faculty of Forestry
carried out inventory work after logging in 1995. This bomb was then disposed by the authorities. There is also a fort in Compartment 1 which used to be a small
hilly area that was later made into a fort during the war.

For full article:

http://www.forr.upm.edu.my/images/ariff/eb...t%20Reserve.pdf

Perhaps it was the presence of bombs that have spared this forest from development up until this point!