Dynamics of forest carbon stocks, fires, and harvest under changing
climatic conditions in the U.S. during the 20th century
Abstract
Wildfires and land use play a central role in the long-term carbon (C)
dynamics of forested ecosystems of the United States. Important
processes include fire suppression during the 20th
century and a recent increase in fire activity, partly due to climatic
extreme events. Although the historical fire narrative in the U.S. is
well understood, its links to changes in forest biomass, resource use
and consumption remain understudied. We reconstruct long-term trends in
biomass burned, and biomass use by humans, integrating various data
sources at different scales (national scale 1926-2017, regional level
1941-2017). We investigate the linear correlation of wildfires and
forest biomass C stocks in comparison to forest uses, i.e., the
extraction of woody biomass and forest grazing, and potential net
primary production (NPPpot). During the
20th century, the reduction in burned biomass and
increase in NPPpot coincide with forest regrowth in the
Eastern U.S., allowing for increased wood harvest. Only in the Western
U.S. these dynamics are less pronounced, indicating that forest fires
and biomass harvest were less decisive factors for forest C stock
developments in this section. In recent decades, linkages between forest
change and wildfires are less straight-forward in all regions,
indicating that past fire suppression levels are less efficient in
present-day forests. Instead, the reduction of harvest in 3 of 4 regions
was correlated to stock increase. We conclude that under changing
climate, present-day fire and forest management practices might be
unsuitable for ensuring both additional forest C sink potential and
expanded wood use.