I think you are onto something. Races would form a relationship with the triffid forest where they harvest the forest. The triffids actually want them to do this because that is how they infiltrate the cities.
The humans for example don't want to cut down the whole forest because then they would have no resources to sustain themselves. If they take too much too fast the forest dies. If they take a certain volume the triffids are able to infiltrate and mind control them. But if they take the right amount, the triffids hypnosis isn't effective enough
It would be an interesting balance that definitely would transform the world