does blackberry produce fruit every year
I have a blackberry tree in my yard and last year it produced a lot of fruit. In past years, it did not bear any fruit. This year it is producing fruit again. The tree has been in my yard for over 30 years.
I believe you may be referring to a Mulberry Tree.
The environment and it's changing weather can effect how much or even if the tree bears fruit.
Many gardeners dislike the mess from Mulberry fruit.
Here are a couple of links.