Now select your tree trunk mesh and activate the Paint Skin Weights Tool. We are going to edit the influence on the each polygon object.
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You will notice that for the tree trunk is being influenced by several leaf joints. This doesn't make sense; the tree trunk is what moves the leaves on a tree, not the other way around. So, select each of the Leaf joints in the Influence window set your Paint Operation to Replace and make the Min value -1 and then set the Value to -1. For each Leaf joint just click Flood. This will remove any influence of those joints for the mesh you have selected.
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When you are finished, you should be able to select each of the Tree_Trunk joints in the Influence window and see a nice overlap of how the tree trunk will deform.
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Let your simulation play out for a decent amount of frames, if you look around your leaves you will see some unnatural stretching
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Select that leaf mesh and activate your Paint Skin Weights Tool once again. Remove influence from any joints that are not apart of the chain you want to influence the leaf. Now find the joint that is the area you want to be influenced.
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Set the Paint Operation to Replace and set the value to 1. Using the brush (you can resize the brush by holding B and dragging with the Middle Mouse Button) paint a few strokes to make the leaves be influenced by only joint. This will solve that stretching.
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You now have a tree that is rigged, set up to react to wind, and weighted to move fairly naturally. Now add lots of key frames, 2000 or so, and select your uniform field. Play your animation (make sure you have play every frame set) and start playing with the magnitude, you can have a gentle breeze wave your tree, or you can have it go nuts in a hurricane! I usually like to write an expression to have the magnitude be influenced by a sin wave. In the magnitude box click and put = (sin(.9*time)*12); now sit back and watch.
