Assuming your tripod is sufficiently sturdy (I'm not personally familiar with the Slik model you mentioned), it sounds like the wind and the long shutter speed were definitely responsible for the blurring you observed.
Going to a faster film, like ISO 200 as you suggested, may not be the whole solution: That'll only take you from 1 sec to 1/4 sec. You're going to have to compromise somewhere. Reduce depth of field by opening up the lens some more (it wasn't wide open, was it?), maybe go without the polarizer and possible tryo a slightly faster film (the Kodak E100VS or E100SW, for example). A combination of these techniques may get you where you need to be. That said, there may not be anything wrong with some of the tree branches being blurred if the rest of the photo is sharp. It can be a pretty nice artistic effect. I've seen some of Clyde Bucher's gorgeous black and white stuff from the Everglades in which many smaller branches are blurred because of the long exposure time. It can work from an artistic standpoint. -- Mark Roberts Photography and writing www.robertstech.com
