In this guided inquiry, students investigate the inhibitory effects of Eastern Hemlock trees on establishment of neighboring woody plants. First, students travel to a mixed-stand hemlock, beech, and maple forest and observe spatial distribution patterns of woody seedlings beneath these three species. Groups of students then design experiments investigating 1) allelopathic effects of hemlock, and 2) non-allelopathic habitat differences (e.g. light availability, soil composition, litter) as explanations for differential seedling distribution. Students then spend 3 weeks inside and outside of lab periods collecting and analyzing data testing their hypotheses, and they present their results in an in-class symposium.
MULTIWEEK - One lab trip (3 hr lab) is used to introduce students to the field site, the forest community, and the problem. Students make preliminary observations and begin developing a proposal. Student groups carry out investigations independently throughout the rest of the semester; typically 3-4 additional lab period-equivalents are needed for data collection, lab analysis, and preparation of the oral report. Part of one lab period near the end of the semester (ca. 15 mins/group) is devoted to oral group presentations.
OUTSIDE OF CLASS TIME:
Students generate their presentations and reports outside of class. Depending on the relative efficiency of different groups, some groups may need or want additional out-of-class time for data collection.
Students submit (i) a one page research proposal, (ii) a primary literature reference list with a minimum of 12 citations about 1 month in advance of the report due date, (iii) their original data, (iv) a lab report composed according to the guidelines below, and (v) they present an oral report during an in-lab class symposium.
Data on the distribution of saplings and seedlings are collected in the field; most groups follow up with laboratory analysis (e.g. soil samples, pH, leaf litter measurements) and/or greenhouse experiments on campus (e.g. effect of soil types on seed germination). This lab can be done in any season, but it is easier to identify seedlings and saplings when leaves are present.
Undergraduate course title: Ecology and Evolutionary Biology, class size: 45-75, class Level: undergraduates, primarily sophomores.
private undergraduate college.
This investigation could be modified as a more structured class project to fit into 1 or 2 lab periods and for larger universities (all students do the same investigation, or groups work on assigned sub-topics). Competitive inhibition in other plant communities can be investigated using the same guidelines used for this lab, but focusing on the potential inhibitory effects of different plant species, e.g. Ailanthus.
photo of Tsuga caroliniana
© JD Skean 2000