Hair Particle System to Create Forest: Some Trees are Floating So I've got a problem popping up. I was following this video tutorial
https://www.youtube.com/watch?v=iPOSAJuoEmU&amp;index=3&amp;list=PLvFQDY1Hrbb41mId9Evuvz3pDrHaGFDYI

I have noticed however that many of my trees are floating above the planes they are supposed to be growing from, which causes the immediate problem of shadows only appearing under some trees. I've checked around online, but most Q&amp;A's similar to this one are because the person didn't use "Hair" or had their trees at the wrong orientation. I have tried to do what these other answers I have suggested but without much luck. 

I don't mind if the distant trees float, but the ones on the closest mountain face are very obvious in the render. So any help would be great! If I have to I will just go through and manually move them if there is a way to do that! I just need them firmly in the ground, so to speak haha. 

Photo time
If the surface that the particles are emitted from is affected by another modifier then you will need to make sure that the particle system's modifier is below the other modifiers. This is so that the particle system can 'see' the previous modifier's result (because blender's modifiers execute in the order they are in the modifier 'stack', with each modifier passing on its data to the next).

Another option you may need is the Use Modifier Stack, found in the particle system's Emission panel. This makes sure the particle system is seeing the 'final result' of all the modifiers being applied to the object before trying to emit particles.