I used to play a lot of acoustic guitar in weird tunings so I'm going to take a guess at this one (but Joe knows David Crosby so it could be anything right?...)
First, Seagull is not in standard tuning either. From the hammer on's and descending run I would say the tuning low to high is DAD(G)BD. (I'm not sure about the G). My reasoning is he hammers on the D chord which means it must still have a normally tuned G and he never hits the high E which is probably tuned to D. The descending little run is still in a standard tuned A string. If I had my acoustic with me I could probably help more.. if I'm helping at all...
He has another chord in there which you don't get a good look at on the DVD but don't assume you can't play chords in open tunings. You just find the strings that make the sound you want and presto!... a chord. Let us know what you discover.
Edited to add: This is the tuning I see Joe using in Seagull... at least to my eyes, so I'm sure PSmith1946 is correct for the Palm Trees helicopters and gasoline tuning as well.