Since the area of a square is sides squared, the area of the square-shaped street is 100*100 = <<100*100=10000>>10000 square meters.
The area of the forest is three times the area of the square-shaped street, a total of 3*10000 = <<3*10000=30000>>30000 square meters.
If the number of trees per square meter in the forest is 4, there are 4*30000 = <<4*30000=120000>>120000 trees in the forest.
#### 120000