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Summer Research Project 2023

  • Title: Faith in a Seedling: controls on and role of forest regeneration at the Harvard Forest
  • Group Project Leader: Audrey Barker Plotkin
  • Mentors: Audrey Barker Plotkin; Lukas Magee; Marcos Rodriguez; Greta VanScoy
  • Collaborators: Daniel Johnson; Sydne Record
  • Project Description:

    Towering trees begin as tiny seedlings, but most seedlings never survive to reach the canopy. What controls which seedlings grow into saplings and eventually reach the canopy? What does the seedling layer contribute to forest function? This summer, we will investigate these questions through long-term field studies, along with some laboratory and remote sensing analyses.

    Students should indicate which sub-project is of most interest on their application essay. Students will focus on one sub-project and will help one another with the different sub-projects, gaining exposure to all aspects of the overall. The entire research group will meet weekly to discuss journal articles and emerging results, and to coordinate work among sub-projects.


    Sub-project 1
    Trees regenerate via seed germination and sprouting after a disturbance, but many forests have a sapling layer of advance regeneration that is already poised to respond (Barker Plotkin et al. 2013). When advance regeneration is present and survives the disturbance, these trees often dominate the composition of the new forest canopy. However, it is unclear what controls establishment of advance regeneration.
    Under what conditions do these saplings establish in the understory of a forest? We will utilize a suite of permanent plots and a browsing exclusion experiment to explore this question. Sixty forest plots represent the range of land-use history and soil characteristics on the Harvard Forest Prospect Hill Tract. These plots were established in 1937, then resampled in 1992 and 2013 (Motzkin et al. ). We will remeasure the overstory trees and dead wood, and collect measurements of the abundance, size, and species of tree saplings. We can then test the influence of land-use history, soils, and overstory tree composition and structure on the sapling layer. In addition, we will examine the potential role of moose and deer browsing in shaping the sapling layer by sampling experimental plots in which fencing is used to exclude browsing. This experiment was established in closed-canopy oak and hemlock forests in 2013.
    Greta VanScoy (field lead) and Audrey Barker Plotkin (analysis lead) are based at Harvard Forest. Greta will typically be in the field with the students, and Audrey will meet with students at least weekly. They plan to work with two undergraduates on this project. This is a field-based project; participants should expect to hike up to a mile to plots, and spend ~8 hour days measuring trees, downed dead wood, and saplings. About 75% of the time will be in the field, and 25% of the time indoors working on data entry and analysis.

    Sub-project 2
    Gap-phase dynamics are the dominant successional process in most forests. Seedlings must survive understory conditions typical of closed canopy forests, including light limitation, water and nutrient competition, and natural enemies. Seedling dynamics are highly size-dependent; however, projecting future forest composition and gap filling relies on passage times from seedlings to trees. Increasing global tree mortality, including high hemlock mortality at Harvard Forest, creates more canopy gaps, more resource pulses, and more opportunities for understory seedlings.

    We will study how seedling dynamics differ between canopy gaps and non-gap areas. The project will focus on the temporal aspect of gap filling such as seedling age to size relationships and passage times to the canopy. Over 500 seedling plots have been installed along a chronology of gap ages at the Harvard Forest ForestGEO plot. This project will leverage these data and also gather additional seedling information by sampling and aging seedling in similar gap conditions off the ForestGEO plot. Project methods include remote sensing to find canopy gaps, a field component to sample seedlings, a lab component to age seedlings, and an analysis component.

    The mentor of this subproject is Lukas Magee, who will assist in all fieldwork and analysis. The initial remote sensing, seedling sampling, and lab work will take approximately 25% of the project time. Another 25% will be dedicated analysis. The remaining project time will be spent surveying seedling plots or assisting with Sub-projects 1 and 3. Fieldwork will be at Harvard Forest; it will consist of ~8 hours per day monitoring and sampling seedlings. Participants will be expected to hike up to three miles and work under variable conditions including hot summer afternoons and biting insects.


    Sub-project 3
    Despite being an important demographic for trees, seedlings are generally neglected when testing ecological theory in forest plant communities. One of the ecological theories being evaluated by this project falls under Metabolic Scaling Theory (MST), an overarching framework that makes explicit predictions about various key properties of communities such as the relative abundance of different sized individuals and the relative distribution of primary production (West et al. 2009). In tandem, these relationships predict that collective energy use of a group of individuals of a certain size is approximately constant, regardless of their body size. However, direct tests of this theory have been focused on larger trees which means that the seedling demography project at Harvard Forest provides a unique opportunity to test the theory for these smaller individuals.
    This sub-project’s participants will be mentored by J. Marcos Rodríguez and will primarily be continuing the regular measurements of seedlings within the ForestGEO at Harvard Forest. Additionally, time permitting, other fieldwork taking measurements of adult trees and saplings in other plots will be conducted throughout the field season to link the dynamics of different size classes. It is expected that approximately 75% of time will be spent in the field while the remaining 25% will be spent on data entry and analysis, although this balance will likely vary throughout the season. Fieldwork will consist of ~8 hour field days carrying up to 25 lb (~11kg) worth of field equipment. This project will also require participants to spend a significant amount of time crouching and kneeling on the forest floor under the conditions of New England summers which include heat, humidity, and biting insects.

    General requirements for all overall project:
    Applicants should be able and willing to conduct the fieldwork, work collaboratively in a team setting, learn new skills, think critically about the research aims, and problem solve in the field. The students should expect to help one another with the different sub-projects, gaining exposure to all aspects of the overall project and developing the ability to negotiate priorities and scheduling. The ability to walk 1-2 miles off-trail with a day pack is required, along the with stamina and humor to work collaboratively in sometimes challenging conditions (whether they be in the field, lab, or computer). Although technical skills such as previous exposure to R and basic familiarity with woody plant species in New England are useful, eager individuals willing to learn these skills are also encouraged to apply.

  • Readings:

    Barker Plotkin, A., Foster, D. R., Carlson, J., Magill, A. H. 2013. Survivors, not invaders, control forest development following simulated hurricane. Ecology 94: 414-423.
    Brokaw, N., and R. T. Busing. 2000. Niche versus chance and tree diversity in forest gaps. Trends in Ecology & Evolution 15:183–188.
    Chang-Yang, C.-H., J. Needham, C.-L. Lu, C.-F. Hsieh, I.-F. Sun, and S. M. McMahon. 2021. Closing the life cycle of forest trees: The difficult dynamics of seedling-to-sapling transitions in a subtropical rainforest. Journal of Ecology 109:2705–2716.
    Farrior, C., Bohlman, S., Hubbell, S. & Pacala, S. Dominance of the suppressed: Power-law size structure in tropical forests. Science 351, 155-157 (2016).
    Motzkin, G., Wilson, P., Foster, D. R., Allen, A. E. 1999. Vegetation patterns in heterogeneous landscapes: the importance of history and environment. Journal of Vegetation Science 10: 903-920.
    Schapira, Z. H., C. S. Stevens-Rumann, and D. Shorrock. 2021. Subalpine tree seedlings: Assessing aging methodology and drivers of establishment. Forest Ecology and Management 497:119516.
    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, Biodiversity Studies