A really simple way to do it is like this.
[attachimg=#]
Make a new power fractal inside the parts shader, or just inside the object if an old multi shader is used, like it is here.
Change all scales of the power fractal to '1'. Displacement doesn't need to be checked so, you can uncheck that now too, if you want, doesn't matter really.
After that, make a new transform shader. This is the scale and speed controls, plug the fractal into it's 'shader' input and the transform shader into the leaf shader's 'displacement function'. Set displacement amplitude to '1'.
Edit the 'translate Y' value by whatever speed the wind should move over the frame range.
At 30 frames per second, '2.5' in the Y input( = 2.5 metres per second, keyframed between f1=0 to f30=2.5) is just over a 5mph breeze.
If you have, say, 90 frames then keyframe from 0-90 with 'translate Y = 7.5m', for a solid movement throughout, or keyframe in between/outside of the frames to have gusts etc. It's up to you.
If you want to rescale the noise pattern, use the transform shader's scale fields to make the 1m fractal a multiplication of whatever you input.
The displacement multiplier in the main leaf shader will control how much the leaf gets bent by the noise. Here it is set to '1'.
This shader preview sequence is equal to 0.5 seconds of movement at the above settings;
[attachimg=#]
Much simpler than you'd think to look at the final results, isn't it? Two extra red shader nodes to create the basis of a wind system!
I've been playing with the redirecting and other things to move the tree trunks as well but the above shows how to blow leaves around with really not very much work at all. Pick any direction/scale/rotation to move the noise. Moving it along the 'Y' just means the noise will roll from the base to the tip of the leaf.
* Another way to shift noise along a leaf is to use Hetzen's constantly moving get frame animator setup, then you control exactly how much wind there is without worrying about the keyframe interpolation, although the interpolation can be very nice to break up consistency.