This sounds like an idea thought up by someone who has basically never thought about the details of such an undertaking. Mars is significantly further from the Sun than Earth, the Sun (giant fucking nuclear fire in the sky) provides all energy for life on Earth. The amount of power received reduces with the inverse square of the distance from the Sun. To grow a forest, you need a temperature that is above freezing. Yes forests can survive periodic cold temperatures, but during such times little to no growth occurs. You need to have liquid water available, and a dense atmosphere with both CO2 and Oxygen present. The amount of energy required to elevate a large volume on Mars to such temperatures would be enormous. The only way you might be able get enough energy would be some sort of nuclear reactor. Using a nuke plant to grow a garden is a bit audacious though. This sounds like the sort of proposal made by someone who thinks we can just all change to electric cars, because you can just plug them in at the wall and get power that is emission free. I really wish stupid hurt, it should hurt, but apparently in this timeline it doesn't.