Greetings and a little question about rhythm

Well, hello to everyone. I've found this forum while looking for information for an essay in Emily Dickinson, and all I can say is that it's really interesting. I would like to see more and introduce myself when I have more time.

Also I'm finding some difficulties with the rhythm pattern of this poem, I would like to think that it is because I'm not native and don't know how to read it:

I died for beauty--but was scarce (...)

you see, in this line, the use of the dash would make it a tetrameter or it doesn't count and is a trimeter?

I'm thankful if you give me your opinions.

Tetrameter. Ignore punctuation and just read the words out loud. That means it has four iambs.

Thank you, Aramis, it is quite easy once you know it and I can apply that to her other poems too.
Thanks.

The '--' is in the wrong place for a normal caesura - it's within an iamb, instead of between two iambs as is usual, but I agree with Aramis here. I suppose that it makes the reader stress the 'but', turning 'ty--but' into a true iamb instead of a pyrrhic substitution.

Whatever the whys and wherefors of the metrical structure though, it's certainly tetrameter - di-DUM di-DUM di-DUM di-DUM.

Besides, stressing the 'but' will stop it getting flabby in later life. ;)

Thanks Xamonas.

And yes, a stressed but is what keeps the world moving!