What Happens:

      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.

______________________________________________________________

Lab Objectives:

     At the conclusion of this multiweek lab, students will:

1. have a basic understanding of competitive interactions among members of a plant community and the ecological and evolutionary consequences of such interactions to plant community structure,


2. have designed and carried out experiments that are derived from two different, alternative hypotheses for the same observed, ecological pattern. They will gain experience evaluating their own methods, results, and conclusions in light of peer researcher's experiments. They will engage in oral and written communication about their scientific findings and discuss outcomes with peer researchers who have investigated yet different alternative hypotheses for the same pattern,


3. master identification of several native trees of eastern deciduous forest,


4. gain experience in the use of appropriate field and laboratory technology and instrumentation and will improve their ability to use computer software programs for statistics, graphics, and presentations,


5. gain further experience with scientific writing and with review and critique of primary scientific literature.

______________________________________________________________

Equipment/ Logistics Required:

* measuring tapes, field guides, surveying flags, compasses,
* soil sample test kits (pH, nitrates, phosphates, etc.),
* canopy sunfleck ceptometer (for measuring light levels) and canopy spherical densiometer,
* electronic balances,
* blender,
* seeds of beech, sugar maple, etc.,
* greenhouse space devoted to course experiments and space in environmental chambers (light cycle, temperate and humidity controls),
* institutional means of transportation to and from field sites.

______________________________________________________________

Summary of What is Due:

     From this multiweek lab, students submit

1. data from the first field lab (Q - do the densities of woody seedlings and/or saplings differ beneath Eastern Hemlock versus Sugar Maple or American Beech)?


2. one-page report describing the statistical analysis and results of the first field lab,


3. one-page research proposal,


4. potential literature cited section, turned in one month prior to the written report due date, with a minimum of 12 primary literature citations,


5. progress report (interview form, about 2 weeks before their final report is due),


6. clearly labeled copies of original data,


7. scientific lab report in the format of "Ecology" and composed according to the guidelines below,


8. oral presentation during an in-class symposium,


9. (optional) - written questions concerning the presentations of other groups, and


10. letter grade (A, B, C, D, F) of their choice for the lab activity and a brief written explanation of the grade given,

______________________________________________________________

Keyword Descriptors:

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