A group of scientists studied some trees in a pine forest. In the densely forested areas, the trees were within 1 m of each other. The scientists observed that these trees had dead branches near the ground. They measured the height above the ground at which the first living branches were found on different-sized trees in the forest. Then they repeated this procedure on the same kind of trees in an open meadow. This graph summarizes the scientists' data. Which inference is best supported by these data?