Pooled across the five dominant species, large trees accounted for 3% of the 636,520 trees occurring on the inventory plots but stored 42% of the total AGC. Large trees accounted for 2.0 to 3.7% of all stems (DBH ≥ 1” or 2.54 cm) among five tree species but held 33 to 46% of the total AGC stored by each species. Tree AGC (kg) increases sharply with tree diameter at breast height (DBH cm) among five dominant tree species. We analyzed forest inventory data collected on 3,335 plots and found that large trees play a major role in the accumulated carbon stock of these forests. We examined the proportion of large-diameter trees on National Forest lands east of the Cascade Mountains crest in Oregon and Washington, their contribution to overall aboveground carbon (AGC) storage, and the potential reduction in carbon stocks resulting from widespread harvest. This study is among the first to report how carbon storage in large trees and forest ecosystems would be affected by a proposed policy. In the temperate forests of the western United States, proposed changes to Forest Plans would significantly weaken protections for a large portion of trees greater than 53 cm (21 inches) in diameter (herein referred to as “large-diameter trees”) across 11.5 million acres (∼4.7 million ha) of National Forest lands. Large-diameter trees store disproportionally massive amounts of carbon and are a major driver of carbon cycle dynamics in forests worldwide. 5The Fletcher School and Global Development and Environment Institute, Tufts University, Medford, MA, United States. 4Woodwell Climate Research Center, Falmouth, MA, United States.3Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, United States.2EcoSpatial Services L.L.C., Flagstaff, AZ, United States.1Eastern Oregon Legacy Lands, Joseph, OR, United States.
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