It's basically vegetal cancer. Any sunny opening is quickly filled and nothing else grows once it is established.
It can still make its way (slower) into shaded forest, where it puts an end to anything else growing too.
So when the tall mature trees die, there is only Japanese Knotweed left.
When weed-cutting maintenance is done by roadsides infested by it, tiny bits in the equipment fall elsewhere, take root and establish new colonies like cancer cells.
It's basically vegetal cancer. Any sunny opening is quickly filled and nothing else grows once it is established.
It can still make its way (slower) into shaded forest, where it puts an end to anything else growing too.
So when the tall mature trees die, there is only Japanese Knotweed left.
When weed-cutting maintenance is done by roadsides infested by it, tiny bits in the equipment fall elsewhere, take root and establish new colonies like cancer cells.