> but it is true that some trees waste product is bioactive and suppresses other plants

That's not waste product. That's just product.

good point. shed those pine needles, somebody else hates 'em so there's no downside now you sucked the vital juices back out of them.

from a different article:

>The roots of the black walnut tree emit a chemical known as juglone. This chemical is toxic to many other plants, and can stunt them or kill them in as little as a month. The toxic area around mature black walnut trees is usually a 50- to 60-foot radius around the trunk, but can be as much 80 feet.

Toby Hemenway has a theory that mulberry bushes can neutralize juglones, and create a safe space in the “lee side”, but I was never clear if that was by root zone exclusion or some other mechanism. If the former, I’m curious to find out if it works with a new mulberry in the root zone of an old walnut.

Allelopathy, of which the black walnut tree is one of the most notorious.