Studying Tree Competition and Mortality

The goal of this project was to explore the relationship between tree growth, competition, and background (unexplained) mortality. This is a project that I conducted as part of a summer internship at Harvard Forest.

In this project, I used both long-term datasets and field-data that I collected. For each 10m diameter forest inventory plot, I matched multiple years of data to determine the annual diameter growth increment for each tree. I also calculated a competition value for each tree in each year. The competition index was based on (1) the ratio of a tree’s size to it’s neighbors and (2) the distance to neighboring trees. I also used time-series analysis to gap-fill values for neighboring trees that did not have data in every year because they were located outside of the plot.

Growth vs Competition Index and Tree Mortality for Three Common Species.

For hemlock, a shade-tolerant species, there was almost no correlation between competition index and growth increment. Additionally, there was no mortality recorded for hemlock trees in this time period, even at high levels of competition.

For red maple, a fairly shade tolerant species, there was an inverse relationship between competition index and growth. However, competition was not an important predictor of mortality because the mortality occurred evenly across the range of competition values.

For red oak, a shade intolerant species, there was a stronger relationship between competition index and growth. Additionally, mortality occurred only at high competition values suggesting that high tree competition may increase likelihood of mortality for red oak.