Carob - does it kill competition?

This year we planted a terrace where about a third of it is under a carob canopy. I've noticed, that "nothing" grows under the canopy. That is to say, that in the spring it was green, but now in summer there is nothing green there. The rest of the terrace is growing and green.
We have many carob trees on our land and after the above observation, I looked at many of them and noticed the same thing. Nothing grows under them. There isn't even dried out grass left from the spring. Only a circle of naked soil, the exact size of the canopy.
This strikes me as odd, since the ground under the carobs is well shaded and usually has better soil because of the tree. I haven't been able to find any literature stating the carob kills competition in the same way as black walnut. I have been able to find others observing the same thing and asking the same question as me. Does carob kill competition?

Since the lack of plants is almost exactly the size of the canopy, I have been thinking. Maybe it's not the roots, who do the damage, but the canopy. The trees are full of ripening pods and the bees are swarming, eating sugars from them. Maybe the trees are dripping sugars on the ground, which inhibit growth?

That's just my thought. Has anyone observed the same thing? And does anyone have an explanation?

I just saw palm bushes growing under carob trees when I was on my way home - so they don't kill every thing.

Question is what else can grow there?

Marcus just notes another interesting thing - under the male tree melissa is growing