Soil Carbon Sequestration and the Greenhouse Effect, Second Edition

Abstract

Woody plant encroachment into grass-dominated eco-systems during the past century has been documented in North and South America, Australia, Africa, and Southeast Asia (Archer et al., 2001) and appears to be a consequence of human land-use activities, primarily livestock grazing and fire suppression (Archer et al., 1995; Van Auken, 2000). Major functional consequences of increased woody plant abundance in grasslands may include alterations of above-and belowground productivity, changes in the quality of lit-ter inputs, modifications to rooting depth and distribution, altered hydrology, and changes in microclimate and energy balance (Scholes and Hall, 1996; Connin et al., 1997; Gill and Burke, 1999; Jackson et al., 2000, 2002; Jobbágy and Jackson, 2000; Chapin et al., 2005; Huxman et al., 2005; Weintraub and Schimel, 2005; Hughes et al., 2006). Additionally, many of the woody plant species encroaching into grasslands are capable of symbiotic N 2 –fixation, adding fixed N to N-limited ecosystems (Rundel et al., 1982; Johnson and Mayeux, 1990; Stock et al., 1995; Zitzer et al., 1996; Baer et al., 2006). These alterations in ecosystem characteris-tics following woody plant encroachment into grasslands have strong potential to modify C dynamics and storage and may influence regional and global cli-mate through feedback interactions (Schlesinger et al., 1990; Ojima et al., 1999; Asner et al., 2004). Despite the possibility that woody plant invasion could influence the carbon cycle at ecosystem and global scales, mechanisms and processes associated with C dynamics and storage in the affected systems are poorly understood (Jackson et al., 2000, 2002; Archer et al., 2001, 2004; Hudak et al., 2003; Wessman et al., 2004).