Abstract
Like cities, forests grow by spreading out or by growing denser. Both inventories taken steadily by a single nation and other inventories gathered recently from many nations by the United Nations confirm the asynchronous effects of changing area and of density or volume per hectare. United States forests spread little after 1953, while growing density per hectare increased national volume and thus sequestered carbon. The 2010 United Nations appraisal of global forests during the briefer span of two decades after 1990 reveals a similar pattern: A slowing decline of area with growing volume means growing density in 68 nations encompassing 72% of reported global forest land and 68% of reported global carbon mass. To summarize, the nations were placed in 5 regions named for continents. During 1990–2010 national density grew unevenly, but nevertheless grew in all regions. Growing density was responsible for substantially increasing sequestered carbon in the European and North American regions, despite smaller changes in area. Density nudged upward in the African and South American regions as area loss outstripped the loss of carbon. For the Asian region, density grew in the first decade and fell slightly in the second as forest area expanded. The different courses of area and density disqualify area as a proxy for volume and carbon. Applying forestry methods traditionally used to measure timber volumes still offers a necessary route to measuring carbon stocks. With little expansion of forest area, managing for timber growth and density offered a way to increase carbon stocks.
Highlights
Measuring forests tells their spatial extent and the density of the trees that occupy that extent
As concerns expand from timber volume to include the attributes of biomass as well as the carbon sequestered in that mass, the attributes must be connected and new coefficients measured
Forests in a single nation with continuing inventory The United States represents a single nation with a continuing inventory
Summary
Measuring forests tells their spatial extent and the density of the trees that occupy that extent. Foresters measured the attribute of merchantable timber, called growing stock, on a given stand to assess its commercial value. As concerns expand from timber volume to include the attributes of biomass as well as the carbon sequestered in that mass, the attributes must be connected and new coefficients measured. The Forest Identity [1] connecting those attributes shows timber volume equals area times density, and biomass equals volume times the ratio of growing stock volume to the biomass of crown, foliage, and roots. Carbon mass equals the biomass times its carbon concentration. Both nature and humanity affect forest area. While climate and geography determine potential forest area, humans determine the hectares they spare from farms, logging, settlement, and transportation
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