Human-generated pattern in commercial forests of southern Mississippi and consequences for the spread of pests and pathogens
Modem management practices have radically changed the spatial structure of pine forests in the southeastern United States. This study quantifies the modern distribution of loblolly (Pinus taeda) and slash pine (P. elliottii) forest at three sites in southern Mississippi, USA, by examination of aerial photographs. Distributions prior to European settlement were reconstructed from soil maps. Before European settlement, loblolly and slash pine were restricted to bottomlands alone. streams, separated from similar stands by 610-950 m of upland forest/savanna. Basal areas of Pinus species were probably <100 >ft(2)/acre. In modem forest. clusters of loblolly/slash stands are separated by only 20-50 m. Clusters are smaller and more circular than presettlement stands, have 89-92% of their perimeter in high-contrast forest edge, and frequently have Pinus spp, basal areas much greater than 100 ft(2)/acre. Modem loblolly/slash forest covers a greater proportion of the landscape than presettlement, extending well into upland areas, and shows greater spatial autocorrelation at scales of 1000-2000 m. These changes have increased the connectivity of the landscape as perceived by the southern pine beetle and fusiform rust, potentially facilitating their spread between previously separated watersheds. We suggest that pests and pathogens can be controlled by separating individual plantations using barrier zones of non-susceptible vegetation 600-900 m wide, i.e. equivalent to the gap between presettlement bottomland communities. (C) 2002 Elsevier Science B.V. All rights reserved.