Using open tunings (sometimes referred to as altered tunings) can be like discovering a whole new world of guitar playing. Essentially, all you are doing is tuning your guitar in a different way than in the standard EADGBE manner. But if you feel your playing is in a rut, it can make exploring the guitar surprising and mysterious again. Songwriters Joni Mitchell, Ani DiFranco, and David Wilcox have all used open tunings as a tool for finding exciting sounds and songs in their guitars.
Some open tunings have become the standard for certain players or even entire genres. DADGAD is possibly the most widely used open tuning, and players such as former Wings' guitarist Laurence Juber have begun performing and composing almost exclusively in this tuning. It has also gained wide popularity in Celtic music circles. Slack Key is a Hawaiian guitar style that relies heavily on open tunings — most often taro patch tuning, which is a way of tuning the strings to a G major chord. Many bottleneck players tune to either open G or open D so that a straight slide will produce a major chord.
The tuning I use for "South Branch" is a derivative of open D tuning, where all the strings are tuned to D chord tones — D, F#, and A. To get this tuning, you'll have to tune your first, third, fifth, and sixth strings lower than standard so that you have DGDF#AD. The fifth string is the only open note outside of the D major triad. It's actually the fourth note of the D scale. You can play a D chord simply by placing a finger on the second fret of that string, or even by muting the string.
Since tuning down loosens the tension on four of the strings, you might find your guitar making some extra buzzing noises. A possible temporary solution is to use heavier strings. I have a special guitar I use for open tunings. It's a bit of a luxury to have an instrument that is set-up and dedicated to open tunings, but it's well worth it if you spend much time doing this sort of thing.
The transcription I've included is very close to what I played on the Coming Home recording. In the video below, I've added a little intro. Basically, it's just harmonics on the seventh and twelfth frets and one little lick based on part of the tune. You might explore the tuning a bit and come up with your own little introduction.
Intermediate and advanced players should be able to tackle this piece. There are a lot of open strings, and that makes it a little easier than it might first appear. Start slow, use a metronome, and feel free to shoot me any questions or comments.
Solo fingerstyle transcription of "South Branch" by Chuck Cheesman ~ pdf file