A permanent plot study provides an amazing opportunity for ecological research because it allows scientists to observe changes over ecological time. While many studies take place over a few field seasons at most because of funding or other limitations, permanent plot studies allow scientists to ask questions that only be answered over years or decades by providing a larger window into the dynamics of a site or population over time. For this reason, permanent plot studies are also essential to studying organisms like trees that grow slowly and often live for a long time.
At 42 years old, the Lyford Grid is Harvard Forest’s oldest running permanent plot study. Soil scientist Walter Lyford, who lived in a house a short walk away, established the site in 1969. Lyford gridded the 2.9 hectare continuous plot into 32 100x100 foot squares, and mapped in each individual tree onto hand-drawn maps. Because Lyford was a soil scientist and had a broad-range of ecological interests, he not only censused all living and dead trees but also recorded the position of rocks and streams, and marked the spatial distribution of soil types in the plot. The detailed maps he created provided the basis for later censuses of the Lyford Grid.
All the living and dead trees greater than 5 cm diameter at breast height (DBH, 1.3m) were recensused by teams of Harvard Forest researchers over the period from 1987-1992, and again in 2001. Additionally, an REU student in 2001 digitized all of Lyford’s maps, preserving the data in the form of ARCView maps of each square in the grid.
The Harvard Forest plans to census the Lyford Grid every ten years, so we were lucky enough to get to participate in its recensusing this year. In the field, we measured nearly 4,000 individuals. Within each 100x100 ft block, we tried to relocate each individual recorded on the maps and datasheets from 2001. When trees have completely decomposed, they are recorded as gone, but more often, we could relocate them in the field.
For each living individual, we measured its DBH, condition (living, dead, etc.) and canopy class (how much of the canopy the tree occupies). For dead trees, we measured the diameter when possible, the length and direction of any remaining piece of the downed tree, and its decay class. During these long days in the field, we became able to confidently identify numerous tree species, effectively combat bugs, and fashionable carry our field gear around using a handy tool belt.
The fieldwork and data entry occupied the first half of our summer, but since finishing this part of the project, we’ve had the luxury of working primarily indoors, analyzing the data. Because our dataset includes over 6,000 individual trees and many variables, we were able to tailor our individual projects to our interests.
My individual project uses the Lyford Grid data to track changes in species composition and their impact on aboveground biomass of the entire forest over time. Many previous studies have suggested that northeastern forests serve as a significant regional carbon sink because trees absorb more CO2 than the ecosystem emits into the atmosphere. However, these studies haven’t investigated how changes in the forest stand might impact the aboveground biomass, and I think that the types and frequencies of trees in the forest should have an impact on the overall carbon sequestration. My results show that biomass in the Lyford Grid is increasing almost perfectly linearly with time, which suggests age is not limiting the forest’s growth. Red oak (Quercus rubra) comprises the majority of the forest’s total biomass at each census. Therefore, in the future, I hypothesize that stand age, species composition, and disturbance patterns will all impact the aboveground biomass of the Lyford Grid and similar temeperate, northeastern forests. I really loved everything about working on this project, from the days in the field to the chance to work really closely with my mentor and other researchers in the Harvard Forest community!
I focused my study on understanding the growth patterns of red maples across environmental gradients. I found red maples to be a particularly interesting to study, for its characteristics of being able to grow on a wide variety of conditions sets it apart from other species. With the Lyford Grid having 42 years of data and detailed information about site history, I wanted to utilize as much of that information as possible. I compared growth rates to soil moisture, site disturbance, size of tree, and competition. The field work component was the most interesting part of the summer. I loved being able to walk a short distance from Shaler Hall to the plot. The part that consisted of checking though and organizing data was nowhere near as exciting as exploring a type of forest that was entirely new to me. I’m leaving this summer with more than I imagined. I know that the learning experience, great friends and unforgettable moments will all be reminisced upon when I think about the Harvard Forest and my first time to the East Coast.