The terraforming of Mars began in the late 22nd century, and was completed in early 25th century. The estimated 100,000 years for tree growth, and oxygen release was a major over estimate based on early 21st century technology. Indeed the planet was warmed up using green house gas factories on the Martian surface along with solar arrays in orbit beaming down heat energy. Water, and dry ice caps released thickening the atmosphere which was mostly CO2.
Then the planet was seeded with rapidly growing genetically engineered plants, and microbes of many varieties. In addition trillions of microscopic nanobots were spread about Mars to act as mini farmers working the land to maximize plant yield, and correct any issues that might arise. The nanobots were controlled, and monitored by a super computer at the Mars Terraforming Command space station in orbit around the former red planet now rapidly turning green, and blue. Near the end of the project the atmosphere finally had enough oxygen to introduce animal life from Earth, and humans no longer needed oxygen tanks to survive as they gaze up at the blue sky above.
In the 31st century Mars is a planet flourishing with pristine life. The equator is a small sub-tropical zone, and zones around it are larger temperate zones. Then a large area of tundra, and an even larger area of Arctic zones at the poles of the planet. From orbit you see a huge areas of white snow, and ice at the top, and bottom of Mars then bands of the familiar red rusty deserts with some green, and white mixed in further toward the equator. Then in the middle the green, and blue of plant life, and the waters of lakes, rivers, and seas. On the night side you can see the lights of the sparsely spread out Martian cities. Under the Mars Conservation Act Of 2614 a limit was imposed on the number, and size of cities. However no definitive limit was put on the population.
For those wishing free land, which is virtually non-existent on Earth now, volunteering in government is required to earn your land since we have no economy with money anymore. Everyone owns nanobots to build whatever they need, energy is free, and resources (base elements to build things) are freely shared as well. The only commodity is land. If someone doesn’t want land, or completes their volunteer program they can effectively choose to retire for the rest of their immortal lives.
Near the completion of the Mars Terraforming Project the Venus Terraforming Project was begun. A challenge far greater in scale than the transformation that took place on Mars. Of course by the 33rd Century we had terraformed worlds in other star systems, and eventually found a number of planets already teaming with life including sentient intelligence.