The International Coordinating Council of the Man and the Biosphere Programme (MAB), meeting this week in Paris, added 23 new sites to the UNESCO World Network of Biosphere Reserves (WNBR), a program of the United Nations.

Proposals for 28 new reserves and site extensions in 22 countries were considered (11 of those reserve extensions were approved and one reserve was renamed). Previously, the network consisted of 669 sites in 120 countries.

At the same time, the council approved requests by the U.S. and Bulgaria to remove some of those countries’ biosphere reserves from the official list. The U.S. withdrew 17 sites (out of the country’s previous total of 47 sites), and Bulgaria withdrew three. Prior to this year, a total of 18 siteshad been removed from the program since 1997, by seven countries.

In statements emailed to National Geographic, UNESCO and U.S. State Department officials said that the 17 sites in question voluntarily withdrew from the program, but some are planning to re-enter at a later date. Nineteen sites in the U.S. remain fully compliant with the UNESCO biosphere-reserve designation, and ten others are under review.

“Withdrawal is not unusual and other countries have withdrawn sites in the past (the U.K., Austria, Australia, Norway, Bulgaria, Sweden), often because there was no human population in the reserves or because of lack of support from local communities,” says UNESCO spokesperson Agnès Bardon in a statement.