Che Smith and Mila Thigpen measure the height of one of the surviving pines.

The BFEC Pine Plantation

In honor of Earth Day 1990, Professor Tom Jegla arranged for the Newark Audubon Society to donate 1000 white pine seedlings (Pinus strobus) to Kenyon College. In April 1990, ecologists Ray Heithaus and Kathy Van Alstyne supervised the planting of these trees at the Brown Family Environmental Center (BFEC) at Kenyon College, on a hillside overlooking the Kokosing River Valley. From 1990 to 2000, students in the introductory biology laboratory continued monitoring the trees.

At the beginning of each growing season, buds on the tips of the branches break dormancy and begin to grow. This growth increases the height of the tree as well as adding a new whorl of branches below the leader and at the end of each branch. The tree pictured on the left has three whorls of branches and is four years old.

Suppose you wanted to know the average height of the trees at the time of planting. Would it be necessary to measure all 1000 trees?


How do you decide what makes an adequate sample?

It depends on:

  • the size of the population being sampled
  • the variability of the group members
  • the size of the population you want to extrapolate to

To get a valid estimate of the average height of white pine trees at the Brown Family Environmental Center, how many trees should you sample?