Question
In certain spots of my yard the grass has quit growing and the ground has a cracked look all around ,is this caused by the trees?

Answer
Elaine:
Trees will compete for moisture with grass, but the cracked soil is from drought and, probably, an uneven distribution of good soil and grass cover.
I would thicken the cover of grass over those areas and nurse it carefully.  Prevention of drought stress requires watering.  Otherwise, there is little else to do but wait until the rain comes.
I would not worry about trees killing grass.  Some of the best winter grass stands is under the shade of trees.