Land Use Change Effects on Forest Carbon Cycling Throughout the Southern United States

Abstract

We modeled the effects of afforestation and deforestation on carbon cycling in forest floor and soil from 1900 to 2050 throughout 13 states in the southern United States. The model uses historical data on gross (two-way) transitions between forest, pasture, plowed agriculture, and urban lands along with equations describing changes in carbon over many decades for each type of land use change. Use of gross rather than net land use transition data is important because afforestation causes a gradual gain in carbon stocks for many decades, while deforestation causes a much more rapid loss in carbon stocks. In the South-Central region (Texas to Kentucky) land use changes caused a net emission of carbon before the 1980s, followed by a net sequestration of carbon subsequently. In the Southeast region (Florida to Virginia), there was net emission of carbon until the 1940s, again followed by net sequestration of carbon. These results could improve greenhouse gas inventories produced to meet reporting requirements under the United Nations Framework Convention on Climate Change. Specifically, from 1990 to 2004 for the entire 13-state study area, afforestation caused sequestration of 88 Tg C, and deforestation caused emission of 49 Tg C. However, the net effect of land use change on carbon stocks in soil and forest floor from 1990 to 2004 was about sixfold smaller than the net change in carbon stocks in trees on all forestland. Thus land use change effects and forest carbon cycling during this period are dominated by changes in tree carbon stocks.

Contributions of secondary forest and nitrogen dynamics to terrestrial carbon uptake

“…This assumption is based on the ecological phenomenon, secondary succession that starts with a disturbance such as forest fire or harvesting, progresses through initial colonization, canopy closure, recovery of species richness, increases in biomass, and ends with a return to the state similar to old-growth conditions (Horn, 1974;Guariguata and Ostertag, 2001). This assumption has also been implemented in previous modeling studies (Ramankutty et al, 2007;Woodbury et al, 2006). Dominant plant functional types could change through time during secondary succession (Guariguata and Ostertag, 2001).…”

Contribution of Agroforestry System in Maintaining Carbon Stocks and Reducing Emission Rate at Jangkok Watershed, Lombok Island

“…Carbon stocks vary according to land use, and are related to tree density and its diversity , soil type and management of land and landscape Woodbury et al, 2006), therefore carbon stocks can be used as an indicator of forest quality. In general, the carbon stock (five pools: trees, understory vegetation, litter, roots and Corg in top 30 cm) in tropical ranges from 350 -500 Mgha -1 (Mutuo et al, 2005).…”

Effects of land use change on soil carbon cycling in the conterminous United States from 1900 to 2050

“…Results for the Southern and Southeastern regions were presented previously [Woodbury et al, 2006]. Herein, we present new estimates of land use changes throughout the entire conterminous USA and use them to estimate effects of land use change on soil and forest floor carbon pools from 1900 through 2050.…”

“…Because the same factors affect carbon emission from soil, the same parameter for each forest type was used for the rate of carbon loss from soil as a proportion of the maximum carbon loss due to deforestation. However, because data from the literature suggest that soil carbon decomposes more slowly than forest floor carbon [Woodbury et al, 2006], an adjustment factor was applied to represent this difference. This adjustment factor was defined as an additional negative exponential equation shown in equation (3).…”

“…This equation provides a better fit to these data (40% smaller sum of squared errors) than do the equations of Hackler [2000, 2001] and West et al [2004] [ Woodbury et al, 2006]. For equation (5), we also show an additional step: multiplying by the area afforested (for example, Table 2) to produce a total change in carbon mass for a region in units of teragrams (Tg).…”