Provide students with the background information, in addition to student instructions and figures, to aid their understanding of figures and associated questions.
Figure 1a is straightforward and illustrates a negative relationship between deer browse and number of medium-sized hemlock saplings on study sites. The sugar maple browse index is conducted by counting the number of browsed and unbrowsed terminal twigs 30-200 cm above the ground. The ratio of browsed to total twigs sampled provides a measure of browsing intensity on a scale from 0 to 1. Thus, 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, also palatable to deer.
Figure 1b has been simplified from Rooney and colleagues’ original representation to ease students’ interpretation. The abundance of hemlocks in each size class depends most strongly on the abundance of the immediately preceding size class. In other words, more large saplings were found where more medium saplings grew and more medium saplings occurred where more small saplings and so on. This is known as “demographic inertia.” Aside from this demographic momentum, a key point for students to realize is that different factors were most important to hemlock regeneration at different stages in their growth. Light availability and ecological subsection (an indicator of different habitat types) affected seedling and saplings, while deer browse influenced the number of medium saplings. As saplings grow, they become more susceptible to browse. This makes sense particularly in the winter when seedlings are covered by snow while taller saplings poking through the snow are vulnerable to deer. Ownership of forest stands strongly influenced the intensity of deer browse. This reflected owners’ different approaches to deer management.
In the first scenario (few hemlocks in canopy but many seedlings and small saplings), management efforts informed by the research of Rooney and colleagues should focus on controlling deer browse through exclosure fences, hunting, or other strategies.
In the second scenario (few hemlocks in canopy and few seedlings and small saplings), management efforts should focus on increasing hemlock establishment by planting hemlock seedlings. In order for this to be successful, control of deer browse could still be necessary to increase recruitment of small saplings into larger size classes.
Additional research could include studies that investigate the effect of other factors not examined by Rooney et al. These include moisture availability and the availability of appropriate microsite conditions like moss beds and nurse logs. Students might also propose research that monitors the effectiveness of their proposed management approaches, investigates methods for reducing deer browse, or examines the effect of deer on other tree species, for example.
For a quick assessment of students’ comprehension of the figures, select one of the questions that students discussed with their neighbor and ask them to answer it individually in writing on a 3x5 index card or piece of scrap paper. Allow 1-3 minutes for students to respond. For a more in-depth assessment, ask students to respond with a short answer in writing to each of the questions in the student instructions.