Tree Mortality Project

    When I tell people that I am studying forest ecology, they probably assume that I am studying the living organisms in forests. In fact, it’s quite the opposite. This summer, I am focused on dead trees. This is because we want to develop a better understanding of the rate of tree mortality and causes of tree mortality here. Trees are an important store of carbon, and tree mortality adds considerable variability to forest carbon dynamics. By sampling recently dead trees, we hope to develop a better understanding of how tree mortality is affecting carbon storage in the forest. The area of forest that I am sampling from corresponds to the EMS (Environmental Measurement Site) flux tower, which has been measuring gas exchange for 26 years. There are many plots radiating outwards from the flux tower that have long term measurements of tree diameter. At each of these plots, we have identified any trees that have died in the past three years. For each dead tree, we assess the potential causes of death, identify competitor trees, then take many measurements. These include the DBH, height, and canopy extent of both the dead tree and competitors, as well as the spatial arrangement of the trees.

    In order to determine if the plot measurements are representative of the surrounding landscape, we have also laid down transect lines connecting the plots and sampled along those transects. We count all of the live and dead trees of each species within 2.5m of the transect lines and perform the same mortality-related measurements as used in the plots for the recently dead tree. We are still working on this part now and will soon analyze the data that we have collected so far.

    One of our transects cuts straight through a stand of red pines remaining from an old pine plantation. The red pines are all dying simultaneously. For most of the dead trees that we have studied, they were shaded out by taller trees, or killed by disease in seemingly isolated instances. However, the pines are completely different. They are the tallest trees around with effectively no competition for light and no visible signs of disease, yet the number of green needles left is dropping by the day. The cause of death is still to be determined, but I heard a rumor that a virus may be to blame? The red pines are quite beautiful trees, and I’m sad to watch them go, right in front of my eyes. However, since I am studying dead trees, the pines present a really interesting situation to observe. Maybe there will be more information by the time you’ve read this. The death of the red pines is still a new occurrence in the Harvard Forest right now.

Laura is a rising Senior at Virginia Polytechnic Institute and State University studying Environmental Informatics.