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Summer Research Project 2019

  • Title: Group Project: The future of the Harvard Forest - Tree seedlings of Prospect Hill
  • Summer Supervisors: Danielle Ignace; Fiona Jevon; Jackie Matthes; Sydne Record
  • Researchers: Danielle Ignace; Fiona Jevon; Jackie Matthes; Sydne Record
  • Project Description:

    Seedlings are often neglected in forest studies, in part because most seedlings do not survive to become adult trees. However, seedlings have the advantage of being amenable to manipulative experiments, and their recruitment and survival are a key determinant of forest regeneration after disturbances. This group project focuses on understanding the role of seedlings within the context of two lines of ecological theory: (1) the theory of energy equivalence, and (2) the Janzen-Connell hypothesis. The four students involved in this project will gain a familiarity with Northeastern forest species, learn experimental protocols for tree demography and physiology studies, and be exposed to cutting-edge concepts in the theory linked to forest ecology. We seek four students to work on three specific sub-projects.

    Sub-project one.
    The theory of energy equivalence in forests suggests that total energy use is constant across different size classes of trees. One reason this idea seems counterintuitive is that seedlings, representing the smallest size class, are shaded by trees in the canopy, and thus have less access to light resources. Theoretical size-frequency distributions based on energy equivalence can be compared with observed forest data; multiple studies of adult trees have found a relationship between size and energy flux (e.g. growth rates) that matches the theory’s predictions, once light availability is factored in. However, these studies typically ignore seedlings and saplings. Our previous work, measuring seedling growth and recruitment at the Harvard Forest, has shown that the abundance patterns predicted by energy equivalence are maintained even in very small size classes. Two students will work on the ongoing seedling demography project in the Harvard Forest ForestGEO (https://forestgeo.si.edu/) plot on Prospect Hill. These students will work closely with the student working on sub-project two. Sydne Record and Paige Kouba will co-mentor the students on this project.

    A typical week for these students will involve about 75% fieldwork, and 25% data entry and statistical analyses. Fieldwork will involve hiking to the ForestGEO plot and taking seedling measurements and helping to transport field equipment for sub-project two. Students will meet with a mentor at least three times per week. They will use R statistical software to analyze the data they collect, and will present these analyses at Harvard Forest’s end-of-summer research symposium. Students are encouraged to ask and pursue independent research questions of their own (which could be the basis for a senior thesis or other undergraduate research paper).

    Sub-project two.
    In addition to continuing the demographic survey in the ForestGEO plot, we intend to measure seedling energy flux directly to test the predictions of the energy equivalence hypothesis. Our results will have implications for the cycling of carbon in this forest ecosystem. We will measure water and energy flux in seedlings by recording light- and CO2-response curves for their photosynthetic rates, and then analyzing leaf samples for C and N content and isotopic composition. This sub-project will involve one student and will take place within the ForestGEO megaplot, so the student on this sub-project will work closely in the field with the two students on sub-project one. Paige Kouba, Danielle Ignace, and Sydne Record will co-mentor the student on this project.

    A typical week for this student will involve about 75% fieldwork, and 25% data entry, leaf tissue analysis, and statistical analyses. Fieldwork will involve hiking to the ForestGEO plot and taking seedling measurements, including gas exchange measurements using a LI-COR 6400 photosynthesis system. The student will meet with a mentor at least three times per week. The student will use R statistical software to analyze the data they collect, and will present their analysis at Harvard Forest’s end-of-summer research symposium. The student will be encouraged to ask and pursue independent research questions of their own (which could be the basis for a senior thesis or other undergraduate research paper).

    Sub-project three.
    The Janzen-Connell hypothesis posits that seedlings that grow farther away from adult trees of their same species might escape pests and pathogens present on con-specific adults and be more likely to survive to adulthood. This mechanism helps maintain diversity in tropical forests, but whether or not it is important for temperate species remains to be explored. This sub-project will experimentally test whether the identity of neighboring adult trees influence the survival and growth of tree seedlings. This sub-project involves planting germinated seedlings of multiple species at several locations throughout Prospect Hill, beneath adults of either their own species or a variety of other species. The student will then track the growth, survival, and leaf condition of these seedlings. This will help us understand whether the adult tree community influences the demographics of seedlings, and therefore the future composition of the forest. Time permitting, this student will also help the students in sub-project 1 with the re-census of the ForestGEO seedling plots. Fiona Jevon will be the primary mentor for this sub-project, and Jackie Hatala Matthes will co-mentor this sub-project.

    Applicants for sub-project 3 should be excited to spend lots of time outside conducting field work. This may involve long days (up to 8 hours) in the field in inclement weather and buggy conditions. Applicants should also be willing to learn basic data entry and analysis in R. The student working on this project should expect to spend 80% of their time in the field, and 20% of their time on data entry and analysis.

    General requirements for all three sub-projects:

    1. Participate in field studies, including ~8 hours per field day crouching in a forest environment to measure seedlings with biting insects and hot, humid conditions.

    2. Hike with scientific gear (30-45 lb. pack) in rough, forested terrain.

    3. Willingness to work in a collaborative team of students and mentors.

    4. Have or develop a basic understanding of R for graphical and statistical analysis.

    5. Think critically about theoretical issues in forest demographics and community ecology and link them to field work and data analyses.

    6. Ask questions about everything from procedures to theoretical implications of our research.

  • Readings:

    Comita, L. S. et al. Testing predictions of the Janzen-Connell hypothesis: A meta-analysis of experimental evidence for distance- and density-dependent seed and seedling survival. Journal of Ecology. 102, 845–856 (2014).

    Farrior, C., Bohlman, S., Hubbell, S. & Pacala, S. Dominance of the suppressed: Power-law size structure in tropical forests. Science 351, 155-157 (2016).

    Packer, A. & Clay, K. Soil pathogens and spatial patterns of seedling mortality in a temperate tree. Nature 404, 278–81 (2000).

    Ruger, N., Condit, R. Testing metabolic theory with models of tree growth that include light competition. Functional Ecology, 26, 759-765 (2012).

    Shingleton A. W. Allometry: The study of biological scaling. Nature Education Knowledge 3 (10): 2. (2010).

    West, G. B., Enquist, B. J. & Brown, J. H. A general quantitative theory of forest structure and dynamics. Proceedings of the National Academy of Sciences 106, 7040-7045 (2009).

    Westoby, M. The self-thinning rule. Advances in Ecological Research 14, 167-220. (1984)

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions, Large Experiments and Permanent Plot Studies, Group Projects