In this guided inquiry, students investigate hypothesized inhibitory effects of Eastern Hemlock trees on the establishment of neighboring woody plants. First, students travel to the study area (Hope College Biology Nature Preserve - a 50 acre parcel of beech-maple "dune" forest) and observe spatial distribution patterns of seedlings that could be explained by competitive inhibition. Following an hour or so of observations, students collect raw data on the occurrence of woody seedlings beneath adult Eastern Hemlock vs. neighboring forest patches under adult American Beech (Fagus grandifolia) and/or Sugar Maple (Acer saccharus). Class data is pooled, and the entire class performs a paired-samples t-test which, at our site, shows a significant reduction of woody seedlings beneath Eastern Hemlock as compared with adjacent sites beneath beech or maple. Next, students are challenged to design a follow-up field and/or lab investigation of interest to them (and that we approve) to explore two alternative hypotheses to explain the initial results. Both hypotheses involve competitive inhibition, but one hypothesis must invoke some form of allelopathic cause for the distribution differences, and the second hypothesis must propose a non-allelopathic mechanism (e.g. light quality and/or availability, differences in soil chemistry and/or physical characteristics, differences in leaf litter under different tree canopies, etc.). Students then spend about 3 weeks to collect and analyze their data, and present their results in an in-class symposium.
At the conclusion of this multiweek lab, students will:
Equipment/ Logistics Required:
Summary of What is Due:
______________________________________________________________ Keyword Descriptors:
From this multiweek lab, students submit
Principal Ecological Question Addressed:
Do Eastern Hemlock trees inhibit the establishment of woody plants of other species
beneath their canopies? If so, what factors are likely to be involved in that inhibition?
Ecological Topic Keywords: community ecology, species interactions, competition, allelopathy, chemical ecology, succession.
Science Methodological Skills Developed: field identification and observation, hypothesis testing, experimental design, evaluating alternative hypotheses, use of spreadsheets and statistical and graphing software, use of primary literature, oral communication.
Pedagogical Methods Used: guided inquiry, student-directed inquiry, cooperative learning, oral communication, written communication, problem-based learning