Trees provide ecosystem services, including oxygen production, wildlife habitat, and climate regulation. They also maintain biodiversity. Understanding the scale of tree populations across the United States offers insight into the health of these natural resources. This article explores how these populations are counted, where they are located, and how their numbers have changed.
The Current Count
The United States is home to approximately 228 billion trees, ranking among the top countries globally for its tree population. This figure represents an assessment derived from extensive data collection. The primary source for this information is the U.S. Forest Service’s Forest Inventory and Analysis (FIA) program.
Measuring Tree Populations
Estimating tree populations across the United States relies on various methodologies. The U.S. Forest Service’s Forest Inventory and Analysis (FIA) program conducts a continuous forest census to measure and monitor forest metrics. This involves field surveys on approximately 355,000 permanent inventory plots nationwide. Crews visit these plots, measuring individual trees for characteristics like diameter at breast height (DBH), height, and assessing their health and any damage.
Beyond direct field measurements, remote sensing technologies play a role. Satellite imagery and aerial photography provide broad coverage, helping to assess forest cover and detect large-scale changes. These observations are integrated with statistical modeling to extrapolate data from sampled plots to wider forest areas. This approach, combining ground-level detail with aerial perspectives, enables scientists to generate estimates of tree numbers and forest conditions.
Geographic Distribution of Forests
Forests in the United States are widely distributed, with characteristics shaped by climate and landscape. Eastern forests, covering about 384 million acres, are predominantly broadleaf species, though the southern coastal region features coniferous forests and plantations. Western forests, spanning approximately 363 million acres, are largely coniferous, including stands in the Pacific Northwest and the Rocky Mountains.
Other forest types exist in the U.S. Boreal forests thrive in Alaska, while tropical forests are found in Hawaii and U.S. territories like Puerto Rico. States such as Maine, New Hampshire, and West Virginia are among the most heavily forested regions. The diversity in forest types reflects varied climatic conditions, topography, and historical land use patterns across the country.
Changes in Tree Numbers Over Time
U.S. tree populations have shown trends over recent decades. While total forest area has remained relatively stable for the past century, the volume of trees has generally increased. Forest growth has exceeded harvest since the 1940s, with increased volume compared to earlier periods. Large-diameter tree populations have increased nationwide, with eastern regions growing faster than western regions.
Several factors contribute to these trends. Reforestation efforts, including large-scale planting in the South, have supported forest expansion. Fire suppression in some areas has also allowed forests to mature. Natural disturbances like wildfires, pests, and diseases impact tree mortality, especially in the western U.S. due to drought and bark beetle infestations. Land use changes, including urbanization, also affect local tree cover, even as overall forest area remains stable.