Impact of land-use change on carbon sequestration in Alabama: interdisciplinary research linking ecosystem processes with economic development

The third Intergovernmental Panel on Climate Change (IPCC) assessment reports indicated the atmospheric CO2 concentration has increased by 31% since 1750 as a result of human activities (2001). The increasing greenhouse gases in atmosphere have led to an increase in the average global surface temperature by about 0.6 oC over the 20th century. Reducing CO2 emission and enhancing carbon storage (sequestration) in terrestrial ecosystems were key issues in the Kyoto Protocol. Terrestrial ecosystems have great potential to sequestrate MORE carbon by increasing forest cover (Tian et al. 2003). As Kyoto Protocol comes into force, carbon is emerging as one of the hottest commodities on the international market place. Increasing carbon storage in lands by land use/cover change could be traded as carbon credits in the carbon market to increase the incomes of local landowners and state economy.

Economic development is the primary driver of land-use change in the southern U.S. (Wear 2002). Historically, human population expansion has converted large amounts of the world’s forest land into agricultural and settlement uses. Concurrent with expanding populations are shifting demographics and increasing urbanization. The rapid rise of urban area is usually at the expenses of forest lands or agricultural lands. However, policy intervention could influence land-use change positively. For example, federal programs such as the Soil Bank Programs, the Forestry Incentives Programs, the Conservation Reserve Programs, and the Stewardship Incentives Programs have encouraged landowners to plant trees and to convert marginal agricultural land to forestry use in the south (Nagubadi and Zhang 2005). These economic development-driven land-use changes directly influence ecosystem processes such as carbon sequestration (Tian et al. 2003; Zhang et al., in press). Land-use changes such as cropland establishment and cultivation, cropland abandonment, and subsequently forest regrowth are the primary mechanisms for transferring carbon between the land and the atmosphere (Pacala et al. 2001; Tian et al. 2003). The terrestrial ecosystems in North America have been suggested as a major carbon sink (Pacala et al. 2001), and a large proportion of this carbon sink is contributed by the terrestrial ecosystems in the southern U.S. region (Zhang et al. in press). We have used the Terrestrial Ecosystem Model (TEM) to examine the effects of land-use change on carbon dynamics in several studies (Tian et al. 2003; Zhang et al. in press). The TEM is a process-based biogeochemistry model that was designed to simulate the dynamics of carbon and nitrogen in terrestrial ecosystems (Tian et al. 1998). Tian et al. (2003) simulated the effects of land-use change, climate variability and increasing atmospheric CO2 concentration on the regional carbon dynamics in monsoon Asia during 1860-1990. Recently, along an urban-rural gradient in Georgia, we have analyzed changes in the types and spatial patterns of land use/cover of three counties and their effects on ecosystem carbon storage (Zhang et al. in press). Our results indicated that, from 1974 to 2002, urban area increased more than 380%, cropland area decreased more than 59%, and forest land increased about 10%. The land-use changes in the three counties resulted in a small carbon sink.

Alabama, one of the largest timber producing states in the US, has experienced tremendous change in land use in the past 30 years due to population increases, urbanization, and economic development (Ahn et a. 2000; Nagubadi and Zhang 2005). Between 1972 and 2000, timberland increased by 7.5% in Alabama but agricultural land decreased by 27%. For the same period, urban area increased by 7.1%, especially in the metropolitan areas of Birmingham and Montgomery (Nagubadi and Zhang 2005). Moreover, pine plantations have appeared to increase significantly in Alabama in the past three decades. In 2000, plantations comprised 24% of the timberland (Boyce et al. 2002). However, the current land-use change data primarily rely on the Census of Agriculture and the Forest Inventory and Analysis (FIA) data, which are available at 5-year interval (Ahn et a. 2000; Nagubadi and Zhang 2004). The high spatial resolution annual land cover data sets of Alabama are not available. It remains unknown how human population expansion, urbanization, and economic development influence land-use changes temporally and spatially in Alabama and the effects of these land-use changes on carbon sequestration during 1970-2004. Furthermore, it remains unclear whether the state of Alabama was a carbon sink or carbon source and how big the sink or source was as the results of the land-use change. Finally, it remains unknown how the carbon sequestration will change in Alabama with increasing population, urbanization, and economic development during 2005-2030.

The overall goal of this proposed study is to examine how economic development-driven landuse changes and projected future land-use changes influence carbon sequestration of terrestrial ecosystems in Alabama. Specifically, we will (1) reconstruct annual land-cover data sets with 1 km spatial resolution from 1970 to 2004 in Alabama including tree plantations using remotely sensed data, the US Census and Agricultural Census data, and other statistical data of land-use change; (2) project future land-cover change from 2005 to 2030 in Alabama using an econometric model (multinomial logit) and spatial explicitly land-use change models; (3) simulate the effects of the past and future land-use change on carbon storage in terrestrial ecosystems during 1970-2030 in Alabama using the terrestrial ecosystem models; and (4) analyze the interactions between economic development and carbon sequestration in Alabama.