Cascades to Coast

Is bamboo an invasive species? Is Horse Tail an invasive species?

Does somebody have to plant an invasive species for it to spread or does it spread on its own?

Is it true that trees can come from places like Japan and can grow well in the US?

Invasive species can spread on their own, but in many cases the first invasive species were planted by humans and then spread. It is true that tress from Japan can grow well in the US.