Trees outnumber people 300 to 1 in the United States, with woodlands covering one-third of the country in the U.S. Forest Service's latest census. Only trees at least 5 inches in diameter are counted in the U.S. Forest Service Forest Inventory and Analysis National Program, which has continuously counted the forest population since 1930.
An acre with at least 10 percent tree canopy qualifies are a forest for purposes of the census, reports Jo Craven McGinty in the Wall St. Journal. Dennis May, a U.S. Forest Service program manager, tells McGinty the census was established to answer the question, "Are we wisely using the forest without impacting its health, condition and stature." 
The U.S. exported $8.7 billion in forest products in 2016 - lumber, paper, logs, veneer, pulp, wood pellets, casegoods and other items - putting the sector right up there with soy beans and corn.
For purposes of the survey, sample areas as surveyed each year, and data is projected to get totals. The Forest Inventory and Analysis National program - which has extensive data at its website - received $75 million to carry on its count last year. Each state's foerst is summarized annuially; and a comprehensive reported is producted in five year intervals. McGinty reports that in the South, longleaf and slash pines are in decline, but overall the forests are stable, she says - though not mentioning the effects of highly visible challenges such as the emerald ash borer, walnut blight, or oak wilt. 
Here's how the U.S. Forest Service Forest Inventory and Analysis National Program summarizes its mission: 
As the Nation's continuous forest census, our program projects how forests are likely to appear 10 to 50 years from now. This enables us to evaluate whether current forest management practices are sustainable in the long run and to assess whether current policies will allow the next generation to enjoy America's forests as we do today. 
FIA reports on  status and trends in forest area and location; in the species, size, and health of trees; in total tree growth, mortality, and removals by harvest;  in wood production and utilization rates by various products; and in forest land ownership.
The Forest Service has significantly enhanced the FIA program by changing from a periodic survey to an annual survey, by increasing our capacity to analyze and publish data, and by expanding the scope of our data collection to include soil, under story vegetation, tree crown conditions, coarse woody debris, and lichen community composition on a subsample of our plots. The FIA program has also expanded to include the sampling of urban trees on all land use types in select cities. 

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