Even though chestnuts can regrow from their roots, this does not usually happen because there are few root systems left in the forest.
chestnuts grow in regions prone to fires.
most forestry professionals no longer want to grow chestnuts.
new growth is stricken with the blight before it has the chance to mature.

New growth is stricken with the blight before it has the chance to mature.

Explanation:

American Chestnut trees can indeed regrow from their roots but due to the devastating effect of the chestnut blight, they have been unable to do this since the blight spread across the country.

The blight was introduced when Chinese chestnut trees were imported into the U.S. in the 20th century. It killed off most of the chestnut trees in the U.S. and attacks the tree again when it grows to around 6 meters bringing it down to its roots. This is why the American Chestnut is considered endangered.

b. the carbon cycle ensures living things have a source of hydrogen