This question is a kind of follow up to this question How to find if a point is inside a mesh?, just in a different context. That is how to basically apply the same thing for curve objects such as tree sapling or ivy curve (from sapling addon and ivygen addon.
I wouldn't prefer converting curve objects to meshes because of large number of them and doing so could quite burden the system memory and rendering time. Besides, converting takes time if you have to performs point-checking quite often.