The ancient ironwood forest surrounding Cao Temple is considered by local people as a priceless and sacred "treasure". They believe that the ironwood forest has existed for a very long time, possibly hundreds, even thousands of years old.

The Cao Temple's genealogy tells that during the Han invasion, a local man hid in the ironwood forest and was saved by a fox when the enemy chopped down the bushes where he was hiding. The people of An Lac believe that the ironwood forest is a sacred place, protecting the ancestors of 12 clans in the area.

Cao Temple's ironwood forest has hundreds of ancient ironwood trees, of which 54 were recognized as Vietnam Heritage Trees in 2011. This is not only a rare green tree population but also an inseparable part of Cao Temple's historical relic site, where five generals of the Vuong family who made great contributions in the resistance war against the Song army are worshiped. Today, Cao Temple's ancient ironwood forest continues to be protected and preserved by local people and authorities as a valuable cultural and natural treasure.