I am a beginner, and i have been cultivating 2 Samanea saman seedlings. i live in Central America and these trees are very common. 
They are both from the same mother tree and are very healthy and growing well in pots. Now i want to commence to Bonsai. 
My question regards just one of them, which is now about 2m tall!! (The other is about 0.4m tall and seems to want to be a small tree already).
My question is; Am i being naive to think i can cut the large one down to size ? The root system is complete, in a large pot. 
the alternative may be to release it to the wild as my garden will not sustain this giant if i plant it in the ground.
This could be a delightful project  
Many thanks,
Giles 

Not that I have experience with the species. But beeing native, has been in pot for a while and grown that much I would definetely try. Start to cut the leader just before a seasonal grow spurt. If it is strong grower all the year it does not matter so much when you do it.

Shose a place where there are a branch growing more upwards than the others. Since you do not yet know how the tree responds, make it quite high. See how the tree reacts the coming year or two. If it backbuds well, be a little bit bolder each year.  Removing more and more of the trunk until final hight.

Within a reasonable time frame formal upright is the style it seems to fit for. Good luck and please keep us updated.

hi Tropfrog! thanks for the advice. my big head scratching is about when to reduce the taproot?? this species is very strong and popular for Bonsai and back budding is not a problem.for this reason  i was thinking about going real hard on the initial trunk reduction and taproot at same time. 

I do not recomend trunk cut and repotting at the same time. But I am growing temperate species in a temperate climate.