Tree Diversity: Quantitative Analysis of Forest Communities Introduction and Methods

Introduction: As a forest grows and develops, it goes through life stages, just like a human does. A newer forest will be different from an older forest that is growing in the same area, simply because it has not had as much time to develop and change. Centennial Woods in Burlington, Vermont is the site of new and old forest habitats. A portion of Centennial Woods was cut down about 200 years ago, and other sections have been cut since then. Logging in Centennial Woods created differences in habitat age throughout the forest; we can split the forest into areas of new growth and areas of old growth. A researcher is able to study the differences in tree size (circumference of tree at breast height), density of trees (number of individual trees per square meter), species richness and species evenness in the two habitats.

For this investigation, our biological hypothesis was that the age of the forest played a role in the size and density of trees within the habitat, and therefore, the older habitat would have larger trees but would be less dense, while the newer habitat would have smaller trees but would be denser.

Methods: In this lab investigation, the class split into groups to perform belt transect surveys. Each group was responsible for a 25 meter-long transect in the old part of Centennial Woods and another in the newer section of Centennial Woods. The group member with the longest arms walked the length of each transect with arms outstretched. Whenever the walker touched a tree that was approximately 5 feet tall or more, the name of the tree was recorded and its circumference at breast height was measured in centimeters. The diameter of each tree at breast height (DBH) was later calculated using the measured circumferences.