Not knowing what kind of tree trees you are referring to, I am going to assume that they were fruit trees. The traditional way to protect fruit tree trunks from heat and sun is to paint them with a thick coat of lime and water. Most of the time the lime and water are heated to make the coating last longer. This method is called whitewashing. The white paint will reflect the sunlight and thus keep the bark cooler.

Some tree trunks are painted with white latex paint to prevent the killing of the bark by sudden temperature changes in late fall and winter. I have been told that adding rabbit repellent to the paint helps protect the tree from winter foraging of the bark.