Allelopathic trees as barrier?

Here you can see the steep hill that is my driveway, this photo shows an area that is 30 feet down to the road below. In the left of the photo you can see a vigorous growth of Himalayan blackberry, the curse of Western Washington. It spreads especially along waterways, from the fruit dropping into drainage ditches, and can never be eradicated from the base of this hill as a ditch carries fresh supplies of it to reseed every season.

I have already planted bamboo in the sandy margin along the edge of that hill between the drop off and the driveway. I figure that the bamboo cannot spread onto the driveway or down the hill, and may serve as a barrier to the BlackBerry.

While reading about where I should plant the American elm graft that I have, I discovered it is the most allelo pathic of all the elms. In my efforts to block out the BlackBerry and make the best use of that sunny hill, it occurred to me that perhaps a line of allelopathic trees, such as black walnut and paw paws and the American elm, will serve as a protective barrier. Function stacking! keep those trees away from other trees that would be sad in their company, and also keep invasives off my property from their main course of entry. Any thoughts?

Just as the pawpaw is not put off by the black walnuts, I wonder if it is similarly resistant to the American elm.

Allelopathy slows down competing plants, sometimes only slightly. It isn't going to act as a barrier but might be one tool amongst a variety of others.

I agree with the above. In my experience allelopathy sometimes stops fragile garden annuals, especially at the seedling stage; to everything else it is at most a modest speed bump or a deterrent, not a barrier. Black walnuts grow wild where I am and you have to look mighty sharp at at species distribution to detect any effect around and under them.  IMO allelopathic effects in general are not to be ignored in designing a landscape, but as an ally against something as vital as feral berry vines I wouldn’t expect much from them.

Thank you both. The way that some of the permaculture literature talks about allelopathic, you would think it was a firewall. I will probably plant those trees in that area if soil conditions favor their development, but I will not expect them to create a magical blockade.