Tree rings,forest composition,and LiDAR reveal historical forests and past agricultural land use at George Washington’s Mount Vernon

Abstract

Tree-ring records of tree growth and age, current forest composition, and LiDAR bare earth elevation models each enable reconstructions of forest and land-use histories. Combining these complementary methods, we investigate the mansion house farm, the remaining portion of George Washington’s Mount Vernon agricultural plantation (Virginia, USA) for environmental legacies that persist from the eighteenth century. Across Mount Vernon, enslaved labor grew tobacco, wheat, and other produce; however, Washington also described the farm as an English landscape design with forests and scattered trees. These methods reveal a remnant landscape of forests and agricultural fields in the mansion house farm that supports historical documents and maps extending back to Washington’s lifetime. Trees dating to the eighteenth century remain on this landscape and are found near steeper slopes. Ordination of present-day forests show a distinct forest composition in locations Washington depicted as forests on a 1793 map. These forests are also associated with older ages from tree-ring samples. A comparison of tree-ring sampling at two spatial scales (1-ha vs 400 m²) shows that selecting trees across a larger scale is more likely to include old trees when considering external, morphological characteristics of tree age. LiDAR terrain elevations show evidence of cross-plowing, an agricultural method frequently used by Washington with ridges and furrows at approximately right angles, in areas that are now forested. The preserved record of past land-use apparent in tree-ring ages, forest landscape composition, and LiDAR bare earth elevations consistently highlights the long duration and pervasive extent of land-use legacies from historical plantation agriculture.