Horses are very intelligent animals.  So, you must treat them as such.  They learn things like we do, by doing them and by being taught about them.  To break a horse that jumps at every little creak of the trees or blowing of the wind or black spot near them you have to work with them.  First of all, if a horse jumps because of whatever.  Stop the horse, calm the horse down, get off the horse and slowly go towards the thing or object that is causing the horse to jump.  Allow the horse to smell, touch and be around that object.  Then get back on ride the horse around a bit, then try it again and see if the horse accepts that object into their lives.  If not, continue to do what I've said above till they do.  After a few times if the horse still doesn't seem to want to get close to whatever object is causing it distress.  Then what you might want to do is get off and walk the horse again right up to the object and if at all possible, tie the horse near the object for a couple of hours.  This allows the time for the horse to get use to the object in it's own way. 

Sometimes, you'll get a horse that spooks just because it gets a rise out of YOU the rider.  They will do this to get YOU off their back.  YOU have to recognize which one it is, is it a REAL spook or not?  If not, then the horse is simply testing you.  So, to break them of this habit, simply do not let out any type of reaction when they spook.  Simply go right on doing what it was that you are doing with the horse.  As if you did not even recognize the spook.  This works most all the time with any horse I've ever riden.  The bottom-line, you have to let the horse know who's boss, in a nice way.  I do not believe in physically harming a horse or any animal for that matter.  They can be taught without force and fear.  They can be taught with love an caring.

Thanks,

DJ