By 2368, the Tagrans' industrial activities had polluted the atmosphere of Tagra IV to a critical point, despite their installation of a thousand baristatic filters in an effort to clean the air. These filters have caused a severe ionization effect in the planet's atmosphere, preventing the function of transporters.
On stardate 46192.3, the USS Enterprise-D mounted a relief mission to assist Tagra IV, one of the largest such missions they had ever mounted. At that time, Amanda Rogers aboard the Enterprise exercised her abilities as a Q to restore the ecosystem of Tagra IV to its natural state, dropping the atmospheric pollutants to less than one part per trillion. (TNG: "True Q")
The exact details of how the planet's ecosystem was restored were kept highly classified. Even as the Dominion was building up its supply lines in the Argolis Cluster, the Jem'Hadar refused to enter the Tagra system believing that whatever restored the fourth planet's ecosystem was related to the disappearance of reinforcements from the Gamma Quadrant in the Bajoran wormhole.
By 2375, group of Human Augments led by Rhys Darcen had colonized an inhospitable desert region on the planet. The genetically engineered intellects of these humans allowed them to, in Snežana Ilochko's words, "tame" the desert making it habitable to various flora and fauna. (Star Trek: Lambda Paz: "Midnight Ride")