Understanding how individual trees interact with their neighbors is essential for developing management prescriptions that support the regeneration and growth of hardwood species.
A newly-funded HTIRC research project led by Drs. Insu Jo and Mike Jenkins seeks to analyze data from the Continuous Forest Inventory (CFI) to discover how species interaction, distancing, management techniques and invasive species effect growth and health.
“I am really interested in forest tree dynamics within temperate forests and what are the consequences of those dynamics and processes,” Jo said. “Mixed forests are quite complex and the tree locations are highly variable. We need to know the effects of those different spatial arrangements and other stand-level conditions on tree growth and mortality. By analyzing the standardized inventory measurements over the years with access to accurate plot locations, I think we can identify some key significant variables and mechanisms of species interactions that can help forest managers.”
Jo and Jenkins will work in conjunction with the Indiana Department of Natural Resources, which maintains the CFI data, as well as other partners at Purdue, Indiana University and the United States Forest Service on the project.
The CFI database, which includes more than 8,000 plots across Indiana spanning nearly 800,000 forested acres and more than 300 million trees, is updated every five years, allowing for researchers to track growth and composition over time. Data includes plot level information including total number of trees within the plot, total biomass within the plot and the number of species within the plot, while also documenting locational data. Data also may include information on management history over the cycle of three or four measurements for each plot.
“When data is collected, not only do we know the center position of the plot, but the angle of the specific trees and the distance from the center of the plot, which will allow us to reconstruct all of the individual trees within the plot,” Jo explained. “That is the novel area of this research, using the spatial inventory data to bridge the gap between individual tree-level interactions and plot-level ecological processes to understand tree species interaction and the effects on tree performance. We should be able to develop some metric information about how species grow bigger or healthier or have lower mortality with certain species. This can provide guidelines for landowners or managers for how to manage particular species with specific interests in mind.”
To begin, Jo will convert the CFI data into an individual tree map based on the field measurements. This will allow it to be utilized in conjunction with LiDAR and high-resolution imagery to match imagery with observations from field foresters.
He will then develop a metric to quantify the impact of neighboring trees on individual growth based on the distance from each individual tree, species competition for light and nutrients and the growth of those trees. This project also will look at how invasive species abundance and soil fertility affect regeneration of tree species and how canopy tree spatial arrangements affect understory invasions.
The CFI database will provide measurements such as tree diameter, species identity and spatial location. Plot level information also includes understory invasive species cover and tree species sapling counts. Soil chemistry data such as pH, organic matter and nutrient concentrations will be integrated through a collaboration with Dr. Richard Phillips at Indiana University.
After the initial mapping, statistical modeling will allow researchers to analyze the impact of different variables on tree growth.
Initially Jo and his collaborators will focus on key economically important species, such as oak, hickory and walnut before expanding their scope. They hope to identify spatial configurations that favor the success of oaks and hickories, while suppressing competition from undesirable vegetation.
The findings of this project should provide advice about management techniques specifically tailored to mixed species hardwood systems in Indiana based on species interaction with neighboring trees and overall overstory spatial structure.
Researchers then hope to expand their analysis outside of Indiana to apply to all hardwood forests in the eastern United States by tapping in the national Forest Inventory and Analysis (FIA) program, which is maintained by the Forest Service.