Martian Green Belt

When the unsettled martian pioneers orbited above Mars, they did so around the equator. On a colder planet the naturally favourable environment would be at the along warmest point. After centuries of struggle, Red Well allowed the terraformation of mars to finally gained footing as plant life was finally seeded into the open martian soil.
The Martian surface was first seeded with modified maples, pines, and even palm trees. The trees were kept protected for centuries, hand pollinated under extreme containment protocols. It wasn't until the martian soil was infested with Red Well that they were able to planted in Martian soil. As the planetary equilirium shifted, more plant species were taken out of storage, including lilies, dogwoods, and rosehip.
Naturally these plants were disseminated around along equator. Lifesupport greenhouses and infrastructure were already established along the equator at this time. Eventually the Red Well allowed them to rapidly extend their range, which caused the oxygenation of the atmosphere and the subsequent ice age. The green expansion of martian ecology wasn't defined as "the belt" until after the ice caps pushed in from the poles. The choice to establish colonies along the equator was a saving grace, as the ice expansion stopped short of burying the colony infrastructures.
It important to note that animals were also reintroduced into forests which nolonger occured on Earth. Most of these animals were carefully introduced to the environment after careful study of their interaction. However some were introduced without official intention, either by escaping from containment or by intentional introduction - for example deer, goats, and seals have both been confirmed to be introduced by errant monks of the Green. There are still controlled lifeforms not allowed outside of containment; for fear of either poor interaction with the ecosystem or damage to it. The best known example being Gigarachnids which is still farmed for their silk.
What was ultimately key to humanities perserverence were the planting of preserved crops including cranberries, carrots, and unfortunately eggplant. Some of these crops have taken root in Mars ecology, and can be found in the wilds far from the belt. The ability of crops in the Mars' Biosphere led to the Martian Food Surplus, which prevented mass starvation during the firwall crisis.
Even under the Martian Ice Canopy, ecology and agriculture continue. Some ecosystems have become isolated within regions formed by ice. Since the Vulcanalia the ice caps have begun receiding during mars close proximity with the newbord star. This created a new season called the thaw. Martian ecologists are uncertain wether this will encourage the Martian green belt or endanger it. Some Martian species appear to be dying out, while other species thought extinct have resurfaced and now thrived in the ever changing environment. One example of this is the reemergence of the japanese snow fairy, a miniscule white bird now widespread throughout the belt.