Weakened

[wasellajam]

Hi, I like this, very relatable and strong images. Some notes:

Weakened

When the workmen descended I like descended here, an attack.
upon the spruce and pine
to protect the electric
pylons they cut a gateway
dissecting the forest,
a slice that severed ancient
limbs leaving a corridor
of sanitised destruction.
These blights to the human eye seem to become a favored path for wildlife dealing with loss of habitat. Don't know if this thought is of any use to you.

When the storm descended Descended seemed odd here, especially because storms don't have the intention of workmen. I'm unsure if that helps or hurts the poem.
to the loch and through the glen
it shook the doors centuries old Still trying to figure out why you don't say "centuries old doors". I know the break on old is good but it reads awkwardly. Doors might not be a bad break either because you're putting humans back in the forest even in this more natural strophe.
and rattled the roots of noble I like this line, it's what scares me during storms.
firs and toppled sycamores,
a swathe that ripped ancient
limbs leaving a corridor "ancient limbs" come off as a bit cliche here, it didn't bother me above.
of natural destruction.
I'm a fan of the five different trees, a mixed forest is a much different image than one or two. 
Now I clamber fallen 
oak where we once laughed.
This would read smoother as "a fallen" or "oaks", I prefer "a fallen" because it gives me room to imagine a comma after clamber if I want to. Love clamber.

I better stop and post this, too much already?  Thanks for posting this, I hope something in there helps.