Wednesday, August 4, 2010

PS 61-139: Reconstruction of historical vegetation in Nevada from 1873 Public Land Survey records

Jonathan D. Wyatt, Virginia Tech and Carolyn Copenheaver, Virginia Tech.

Background/Question/Methods

Public Land Survey (PLS) records have been used as a historical reference for vegetation distribution prior to European settlement of North America. The PLS was performed in the states west of the original thirteen colonies, before widespread European immigrant settlement. The PLS was performed to measure the land for sale to the general public.  In the process of surveying these lands witness and bearing trees were recorded as additional location references for survey benchmarks. The surveyors also described the terrain, vegetation and disturbances of the lands they surveyed. Many researchers have made use of the witness and bearing trees to reconstruct pre-European settlement vegetation, however the descriptions are less commonly employed. Our research objective was to use the surveyor’s descriptions to reconstruct the vegetation from northern Nevada and then to test for relationships between the distribution of vegetation and soils, topography, and climate. Using PLS descriptions in combination with Geographic Information Science (GIS) a pre-European settlement vegetation distribution map will be reconstructed from the township line descriptions. Environmental variables available in existing GIS databases will be overlain on the historical vegetation and chi-squared contingency table analysis will be used to test for relationships between soils, topography and climate.

Results/Conclusions Using the descriptions of the vegetation provided by the PLS proved sufficiently detailed to make large-scale vegetation boundaries (e.g., ecotones between grassland and pinion-juniper forest) able to be reconstructed. These ecotones between vegetation types were influenced by environmental factors with topography and soils being the most important factors. These results are promising, because in many regions of the United States, the PLS records did not include witness or bearing trees, but all PLS records have the descriptions that were employed in this study. Our successful reconstruction of regional-scale historical vegetation opens the opportunity for other reconstructions in areas previously excluded.