Harvard Forest >

Summer Research Project 2020

• Title: The Future of Harvard Forest: Xylem vulnerability to cavitation Project
• Group Project Leader: Sydne Record
• Mentors: Noel Michele Holbrook; Anju Manandhar
• Collaborators: Kate Johnsen
• Project Description:

  Please note: This project will work in collaboration as a group project with other projects listed under "The Future of Harvard Forest"
  
  Over-arching Intellectual Theme
  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. The four students involved in this project will gain a familiarity with Northeastern forest species and learn experimental protocols for tree demography, ecophysiological, and biogeochemical studies. Students will also be encouraged to link their findings to theory within the ecological literature. We seek five students to work on three specific sub-projects and except students to spend some time collaborating within the sub-projects to gain exposure to different methodologies.
  
  Xylem vulnerability to cavitation Project
  Recent advances towards a general solution to the basic question of why trees die under water stress have set the scene for a major leap forward in the prediction of when forests will suffer drought damage. These advances point unequivocally to the failure by cavitation of the water transport system as a universal threshold for plant mortality under water stress. With this important revelation we are, for the first time, in a position to begin to define quantitative limits to the survival of diverse plant species. The goal of our over-arching project is to predict how climate-change droughts will modify forests in the future. The student will assist with measuring xylem vulnerability to cavitation in branches of canopy trees and seedlings of the same species. We will use the optical method, developed by Tim Brodribb, which provides an efficient and reliable way to assess xylem vulnerability in the large numbers of species. This technique records xylem cavitation optically with specially designed cameras (see www.opensourceov.org), and in combination with fitted psychrometers, measures stem vulnerability to cavitation in branches. Midday water potentials of both canopy and seedlings will also be measured. The goal will be to characterize the susceptibility to drought of the most common canopy tree species and to assess how this varies with ontogeny (i.e., seedling to adult). Two students will work on this project and be co-mentored by Missy Holbrook and Anju Manandhar.
  
  A typical work week for the students working on this subproject will include about 50% field work (sampling branches and measuring leaf water potential) and about 50% lab work. Lab work will consist of setting up and monitoring the optical sensors and psychrometers, as well as image analysis of the data. The Harvard Forest canopy lift will be used to collect branches and leaves from mature trees. Students will learn tree identification, new techniques in xylem physiology and plant water relations, image processing and data analysis, basic statistics and interpretation of physiological data. Students are encouraged to develop an independent component of the research focusing on seedlings. For example, a student could relate time since last rainfall to seedling water potentials and thereby assess the potential for catastrophic xylem failure in seedlings compared to adult trees.
  
  
  General requirements for all overall project:
  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 ecophysiology and link them to field work and data analyses.
  6. Ask questions about everything from procedures to theoretical implications of our research.

• Readings:

  Brodribb, T.J., Carriqui, M., Delzon, S., & Lucani, C. (2017). Optical measurement of stem xylem vulnerability. Plant Physiology 174, 2054-2061.
  
  Choat, B., Brodribb, T.J., Brodersen, C.R., Duursma, R.A., Lopez, R., & Medlyn, B.E. (2018). Triggers of tree mortality under drought. Nature, 558, 531-539.
  
  Kavanagh, K. L., Bond, B. J., Aitken, S. N., Gartner, B. L., & Knowe, S. (1999). Shoot and root vulnerability to xylem cavitation in four populations of Douglas-fir seedlings. Tree Physiology, 19(1), 31–37. doi: 10.1093/treephys/19.1.31
  
  Merow, C., Dahlgren, J.P., Metcalf, C.J.E., Childs, D.Z., Evans, M.E.K., Jongejans, E., Record, S., Rees, M., Salguero-Gomez, R., & McMahon, S. (2014). Advancing population ecology with integral projection models: a practical guide. Methods in Ecology and Evolution 5(2), 99-110.
  
  Messerli, J., Bertrand, A., Bourassa, J., Bélanger, G., Castonguay, Y., Tremblay, G., . . . Seguin, P. (2015). Performance of Low-Cost Open-Top Chambers to Study Long-Term Effects of Carbon Dioxide and Climate under Field Conditions. Agronomy Journal, 107(3), 916. doi:10.2134/agronj14.0571
  
  Miglietta, F., Hoosbeek, M. R., Foot, J., Gignon, F., Hassinen, A., Heijmans, M., . . . Wallén, B. (2001). Spatial and temporal performance of the MiniFACE (Free Air CO2 Enrichment) system on bog ecosystems in northern and central Europe. Environmental Monitoring and Assessment, 66, 107-127.
  
  Okada, M., Lieffering, M., Nakamura, H., Yoshimoto, M., Kim, H. Y., & Kobayashi, K. (2001). Free-air CO2 enrichment (FACE) using pure CO2 injection: System description. New Phytologist, 150(2), 251-260. doi:10.1046/j.1469-8137.2001.00097.x
  
  Pepin, S., & Körner, C. (2002). Web-FACE: A new canopy free-air CO2 enrichment system for tall trees in mature forests. Oecologia, 133(1), 1-9. doi:10.1007/s00442-002-1008-3
  
  Record, S., Kobe, R.K., Vriesendorp, C.F., & Finley, A.O. (2016). Seedling survival responses to conspecific density, soil nutrients, and irradiance vary with age in a tropical forest. Ecology 97(9), 2406-2415.

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