In preparation for class discussion, examine Figures 1a and 1b. Begin with Figure 1a, which relates the number of medium-sized hemlock samplings found per hectare at 100 study sites with an index of deer browse intensity called the “sugar maple browse index.” The sugar maple browse index is the ratio of browsed sugar maple twigs to total sugar maple twigs counted in an area. It provides a measure of deer browsing intensity on a scale from 0 to 1. The higher the sugar maple browse index for an area, the higher we assume the intensity of deer browse to be for other species, including hemlock, that are also palatable to deer. Turn to your neighbor and first describe and then analyze Figure 1a. Take your time and make sure you understand the axes and the variables plotted. What conclusion do you draw regarding the relationship between medium-sized hemlock saplings and deer browse?
Once you understand Figure 1a, take a look at Figure 1b. Figure 1b includes additional variables, including light and ecological subsection (broad, ecologically distinct regions characterized by geomorphology, soils, and potential forest cover types), which affect hemlock trees at different stages of growth. In addition to varying in ecological characteristics, the stands also varied in ownership, which included county, state, and national forests, national lakeshore, Indian reservations, and private lands. The thickness (not length) of the arrow represents the strength of the relationship. Take time to examine the figure and understand which factors influence hemlock at different stages of growth.
With your neighbor, “talk out loud” and explain what you see in Figure 1b. Describe the relationships illustrated - what leads to what? Refer to the following questions to help guide your analysis of Figure 1b:
Once you and your neighbor are confident that you understand the relationships illustrated in Figure 1b, imagine that you are the managers of a protected forest area in northern Wisconsin. This forest has been historically dominated by hemlock, and you would like to restore hemlock in stands where it once existed but now is rare. You are responsible for developing a management plan for hemlock regeneration based on your understanding of the factors that most affect hemlock establishment (initial growth as seedlings) and recruitment (progression into subsequent size classes as saplings). Consult with your neighbor and discuss the following questions: