Historical land use has been a pervasive driver of forest dynamics in the eastern deciduous forests of North America since European settlement. This presentation considers the impacts of colonial plantation agriculture on the distribution of tree age within forests at George Washington's Mount Vernon plantation. Because of its preserved status extending back to at least 1853, the Mount Vernon plantation has been removed from much of the subsequent land use impacting adjacent areas. Thus, it provides a unique setting to focus on the long-term forest response to colonial land use near Washington, D.C. Specifically, this presentation focuses on the effect of two nonrandom sampling designs on estimations of stand age across this former plantation. Using both selective and systematic sampling designs, this study questions whether these designs produce equivalent estimates of stand age. Age estimates across the property are also compared to an independent set of georeferenced historical maps delineating forest cover at Mount Vernon.
Results/Conclusions
During the summers of 2008 and 2009, 59 circular plots (0.04 ha) were established within the historical Mansion Farm area of the plantation. These plots were placed systematically within one-hectare grid cells with at least 50% forest cover. More than 1,000 standing live and dead trees greater than 10 cm DBH were surveyed, recording species, DBH, growth status, and canopy status. Two co-dominant trees were cored within each plot to estimate stand age, comprising a systematically sampled dataset of approximately 100 trees. At least one additional co-dominant tree across the entire one-hectare grid cell was also cored in an effort to identify the oldest tree in that grid cell, comprising a dataset of approximately 50 selectively sampled trees. While both sampling designs located trees extending back to the eighteenth century, age estimates (based on earliest crossdated ring) are significantly older using the selective sampling design than the systematic sampling design. However, a comparison of historical georeferenced maps displaying forest cover from 1793, 1862, 1933, show agreement with estimated tree ages from both sampling designs, identifying an area of persistent forest cover extending back to Washington's tenure.