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Harvard Forest REU Symposium Abstract 2019

  • Title: Varying methods of Leaf Area Index measurements in temperate broadleaf forests of the Northeast
  • Author: Ilana S Vargas (Colorado State University)
  • Abstract:

    Leaf area index (LAI) is a commonly used measurement to detect changes in forest canopy density. It measures canopy density by calculating the amount of leaf area in square meters for every square meter on the ground. Variations in canopy cover directly impact light transmission, the fraction of absorbed photosynthetically active radiation (PAR), and available light for plants and trees below the top of the canopy. Using data collected from the Harvard Forest Walk-Up Tower, we were able to identify the relationship between LAI and intercepted PAR. The relationship between LAI and light transmission, as described in the Beer-Lambert Law, is used in modeling photosynthesis rates and atmosphere-ecosystem interactions such as carbon exchanges. The accuracy of LAI readings is imperative to the success of future models. The consistency and accuracy of different LAI measurements were compared to find the best method. LAI data were collected at 18 plots by the Licor-2200C plant canopy analyzer. Hemispherical photos were taken at each plot as well and processed through RStudio and Winscanopy for comparable LAI measurements. Typically, LAI measurements are taken in diffuse light. Different factors were considered, but measurements were taken in varying light conditions including direct sun, dusk, and dense cloud cover to compare techniques. Although there is a translucent filter to simulate diffuse lighting during full-sun conditions, measurements taken in dense cloud conditions and at dusk tended to result in more consistent and precise LAI readings. Using accurate LAI measurements with intercepted PAR data we further analyzed the relationship of forest atmosphere exchanges. Extending this study by continuing LAI sampling in varying light conditions and through different methods could determine the best way to measure canopy density.

  • Research Category: Forest-Atmosphere Exchange; Group Projects