I had 2 large Castor oil plants/trees in the garden, they've been there for ~5 years exploding their seeds all over the place. I learnt they have a lot or ricin in them and since I got a new fury friend and they were exploding >30 seeds a day all over the garden, I chopped them down.

I only had the 2 plants/trees, none anywhere else.

Within a week of chopping them down I've had 10~60 sprouts a day.

What is the phenomena called which prevents seedlings sprouting while the source is still alive, but when it dies it triggers a sprout command?

I find it totally amazing bcos some are in a completely different part of the garden separated by an entire house, and contained in a separate elevated earth bed.