Had a Miscantus sinensis ‘Silberpfeil that reverted from being variegated to becoming plain green once. On the genetics you also have the opposite happening, you get a spontaneous mutation that gives you a new variety. This is quite common in for instance tulips and apparently there are quite a few in commerce.
There are many ways to clone a tree, but the specific method would be depending on the species. The simplest way to clone a tree is by cuttings. This can be extremely easy or indeed very hard or even impossible, again depending on the species.
Some trees like magnolia for instance, can be layered if there is a low enough branch to bend down, or you can use air layering. You can also obviously graft many species, even many conifers can be grafted, but the success rate is lower than with say an apple tree. Tissue culture should also be an option. There is also a few other options.
Generally speaking in a forest, trees often germinate after a forest fire, when a tree falls down (they actually often grow in a straight line, germinating on top of the decaying tree trunk) or when the ground has been disturbed for some reason. It can be very difficult for some species to self seed. Others of course are more like weeds.
Also in a garden generally you cut your grass and no tree seedling survives being decapitated! There is also no guarantee that a seedling or even seed survives your winter... Maybe you will need to give your seeds some protection for the winter. Sometimes a simple cold frame goes a long way. Another factor may be that you probably would have better seed if you had another tulip tree nearby. But sorry, for the your tulip tree, I have no specific knowledge.They aren't very common here, but an interesting species, no doubt.
