Birches bend and shed their bark, but should they bend for me?

[milo]

Birches bend and shed their bark
to conquer obstacles impending
for every leaf to reap the light
to start anew each season’s ending

what is "obstacles impending"?  It looks like you mean to say "impending obstacles" but are stuck for a rhyme so you invert the word order.  Doing this makes your writing appear clunky and forced.

Now several transformations in
the birches soon will share their home
and hardy branches weaved through kin
will find their passageways are blocked

"Now several transformations in the birches soon will share their home" - you seem to have some grammatical confusion here.  How does a transformation share its home?

And foreign structures standing tall
where once were only forests vast
containing creatures unfamiliar
present extraordinary tasks

"forests vast", "creatures unfamiliar" - again, you are twisting the natural word order to force a rhyme  Better idea to search for better wording until the flow is natural.

With might and careful adaptation
the birches twist and find their path
through hesitant amalgamation
forming bond to thrive as one –

but bending to the will of none

Kind of messed up the scheme here at the end, easy enough to fix though - 

With might and careful adaptation

forming bonds to thrive as one –
through hesitant amalgamation
but bending to the will of none

You might want to go through carefully and analyze your grammar and logic to make the poem read more naturally as well as edit.

Thanks for posting.
Good Luck.