I suspect if they do, they'll be using much more prosaic stuff like cabbages, as they have the big advantage of being edible.

Light for photosynthesis won't be a problem, as an overcast day on Earth is much darker than a sunny one on Mars. And cloudy days don't happen on Mars, the worst would be a thin haze in a dust storm.

Resin

Jujube tree.

I guess this is one good use for ailanthus! But I couldn't stand the thought of seeing another planet covered in them...

buckmaster,

You beat me to it, on both points!

Baobab trees.

Either that or hickory. That way the martian squirrels have something to eat and the martian dogs have something to chase.

A carob tree is a nitrogen fixer and also produces tasty seed pods for the Martian squirrels, and is very drought resistant.

Right now they most likely are already testing transgenic trees in the lab, putting them under the Mars climatic conditions. By 2015, they will have a tree that can survive on Mars(in theory).

What an interesting question. I suggest russian olive (Elaeagnus angustifolia), it seems to be able to live anywhere. It's drought resistant, cold hardy, and prefers alkaline soils.

Of course, the tree of heaven, Ailanthus altissima.

na, not likely. Its not that cold hardy.

Pinus aristata, Pinus mugo, Pinus banksiana, Pinus contorta, Picea glauca, and Picea pungens are some I think might handle Mars.

"Pinus aristata, Pinus mugo, Pinus banksiana, Pinus contorta, Picea glauca, and Picea pungens are some I think might handle Mars"

Nothing from Earth will be able to cope with Mars outdoors - it is all but a vacuum there, and what little atmosphere it has, is nearly all carbon dioxide.

For an inside environment made habitable for astronauts, those trees won't be able to cope with the lack of a winter. It'll be kept at a constant 20°C or thereabouts for the comfort of the astronauts.

Sorry!

Resin

Sorry, I meant under a dome that would moderate the low temperatures like scotjute said. He mentioned that some northern conifers might be suitable so I listed a few that can candle alkalinity and and drought.
A constant 20 C would open allow for a wide diversity of trees.

I was assuming a garden would be separate from living quarters. Either a larger dome over a smaller living quarters or more likely sort of a foyer to a cave. This would aid in moderating temp.s somewhat and might provide extra protection from small meterorites dust storms, etc. Sort of a layer of protection before you hit the great outdoors of Mars. But who knows how it would be configured. Perhaps someone from NASA should chime in.

If they set up a green house just for plants,then couldn't they also program it's inside atmosphere with a rise and fall of temperatures for daily highs and lows plus seasonal highs for summer and freezing temperatures for winter.Then wouldn't you get condensation from the flucuating temperatures that would allow cold hardy trees and plants to grow?
If they find some sort of water source on Mars,enough that they could melt and bring the inside of there greenhouse to 40 or 50% humidity,That should be enough for a variety of plants.
Don't they have plants growing on the space station?
If they can do it there,they should be able to do it on Mars.

lp

Too expensive. They're not going to cart huge amounts of building materials to Mars just to install a fancy greenhouse. It'll be the absolute bare minimum. Insulation, and not enough room to squeeze in any sardines, let alone swing a cat. Think what you'd want to build with materials at something like $1,000,000 per kg weight lifted off Earth.

The 'foyer' will be triple-glazing with vacuum between the layers; anything else more voluminous just isn't going to work.

Personally, I don't think it'll ever happen anyway. You can do almost as much with robots now for a hundredth of the cost. The technology to put men on Mars exists, but the money doesn't.

Resin

There likely won't be domes on Mars anyway. The radiation hitting the surface due to the lack of any appreciable atmosphere, ozone layer or magnetic field would make it too dangerous to humans and plant life. A colony would have to be buried in the regolith, either in natural cave formations, burrowed into a hillside, or simply by dumping dirt over pre-made habitats. Living conditions would be cramped, as it costs money to send materials to Mars and every square foot of space would be at a premium. In that case, a hydroponics bay producing food would be about it for plant life.

Anything that persists well in shade, because mars is that much farther from the sun. Unless you have controlled environments and lighting, then you could grow whatever the heck you wanted there.

Last summer the Phoenix Lander found ice in the top two inches of Martian soil. Suppose they drilled hundreds of feet deep, would they find liquid water? Would it have the same qualities as water on Earth? Seems like these questions must be answered before planning a greenhouse on Mars.

Believe me, if there was anything that was wver able to survive/thrive anywhere, it would be alianthus, the tree that stinks to high heaven.

"Suppose they drilled hundreds of feet deep, would they find liquid water?"

Realism hits again . . . who is going to cart a big drilling rig, and power source to use it, all the way to Mars?

Simple answer, no-one. We can never know if there is liquid water there or not.

Resin

Well, the original poster does pose an interesting, if completely hypothetical (viewed in light of current financial and political realities), question.

However, the correct answer is "no tree!" Why? Well, because any attempt to establish any sort of outpost of any kind on Mars or other extraterrestrial venues would require plant material which would have a tremendous capacity for growth, and trees are much, much too slow. In fact, I suspect that the main type of plant material which would be used on the first few missions of this type would probably be certain kinds of green algaes, which would grow quickly on the waste nutrients (sewage and garbage) generated by the crew and any animals with them, purify the environment, produce oxygen, replicate themselves extremely rapidly and produce a tremendous amount of biomass that could be recycled into food or fuel. There are certain algaes that definitely fit that description.

Long range, I suppose that trees and other higher vascular plants could be used to provide food, oxygen, fuel, purification of water, etc., in extraterrestrial colonies, and even possibly be used to terraform an alien world like Mars, as was suggested by Carl Sagan and others many years ago. I still think, though, that trees would be among the LAST to go, since they take SO long to grow compared to other plants. Things with the growth rate of water hyacinths, certain grasses, amaranth, etc., are more likely candidates.