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They are easy to clone from cuttings, used as forage for livestock in much of the world. Can be grafted with figs, and fruit at the time as blackberries. Making them a good trap plant for birds. The idea being, if the birds will eat the mulberry and leave the blackberries alone.

I did not know that a person is able to graft a fig branch onto them! That is neat. Do livestock just eat the berries or do farmers use them in another way?

Livestock will eat the leaves and twigs.

Does a person need to prune the mulberry tree (in order for the livestock to be able to reach the branches) or will the tree branches grow close to the ground (I am not real familiar with the growing habits of mulberry trees)

Cut and carry. Thats means the fodder is cut by people and carried or hauled to the livestock. Seen it done lots of ways. The trees are often polarded. Holly will grow into small trees, however most of the time it is cut into hedges. I have used that one for winter sheep fodder. Have to be carefull with holly, the berries are poisonous. Holly is really priklet at the bottom, but as the tree grow taller pass browes height the leaves become less prickly. Holly is often used as a animal fence via hedge laying.

How tall does Holly grow? And how close together is it planted to each other (if its used as a hedge row)?

How tall depends on the variety. I have seen it grow 30 feet tall. Look up "laying a hedge" on youtube. They are not planted super close, they are laid over and woven together.