The researchers studied how to estimate forest productivity in areas with different tree densities and structures. They looked at redwood trees in a forest in California and found that a new index based on tree growth was better at predicting productivity than the traditional method. They discovered that individual redwood trees grew faster in areas with fewer trees and higher productivity index. This means that after cutting down some trees in a forest, the remaining trees will grow differently depending on how crowded the area is and how productive the trees are.