Using a long-established theory of ecology called metabolic scaling, a Northern Research Station scientist and his partners examined the status and recent changes in tree density across all U.S. forests. They found that U.S. forests are becoming increasingly crowded, a fact that has implications for future tree mortality and forest resiliency in the face of global change.

A new study of United States forest size-density trends over the past two decades has produced a novel, nationally consistent baseline assessment of current forest relative density. The number of trees that can occupy any given space—live tree size-density metrics based on metabolic scaling theory—has informed the management of forest stands for decades. Coupling these long-standing theories/applications with modern day, national scale digital forest inventories enables rapid, robust assessment of forest densities. A Northern Research Station team found that over the past 20 years, U.S. forests are growing increasingly dense across most of the nation and are nearing relative densities that may make them more vulnerable to disturbances such as droughts or major insect outbreaks. Notably, the area of high relative density stands has quintupled over the past two decades while the area of least stocked forests has decreased 3 percent. This baseline assessment could assist managers and policy makers in decision-making across scales (stands to landscapes) related to future forest carbon trajectories, land use planning, potential risks to disturbance, and strategies to increase resilience of U.S. forests in the context of global change.