title: Evaluating a new method for reconstructing forest conditions from General Land Office survey records.
abstract: Historical forest conditions are often used to inform contemporary management goals because historical forests are considered to be resilient to ecological disturbances. The General Land Office (GLO) surveys of the late 19th and early 20th centuries provide regionally quasi-contiguous data sets of historical forests across much of the Western United States. Multiple methods exist for estimating tree density from point-based sampling such as the GLO surveys, including distance-based and area-based approaches. Area-based approaches have been applied in California mixed-conifer forests but their estimates have not been validated. To assess the accuracy and precision of plotless density estimators with potential for application to GLO data in this region, we imposed a GLO sampling scheme on six mapped forest stands of known densities (159-784 trees/ha) in the Sierra Nevada in California, USA, and Baja California Norte, Mexico. We compared three distance-based plotless density estimators (Cottam, Pollard, and Morisita) as well as two Voronoi area (VA) estimators, the Delincé and mean harmonic Voronoi density (MHVD), to the true densities. We simulated sampling schemes of increasing intensity to assess sampling error. The relative error (RE) of density estimates for the GLO sampling scheme ranged from 0.36 to 4.78. The least biased estimate of tree density in every stand was obtained with the Morisita estimator and the most biased was obtained with the MHVD estimator. The MHVD estimates of tree density were 1.2-3.8 times larger than the true densities and performed best in stands subject to fire exclusion for 100 yr. The Delincé approach obtained accurate estimates of density, implying that the Voronoi approach is theoretically sound but that its application in the MHVD was flawed. The misapplication was attributed to two causes: (1) the use of a crown scaling factor that does not correct for the number of trees sampled and (2) the persistent underestimate of the true VA due to a weak relationship between tree size and VA. The magnitude of differences between true densities and MHVD estimates suggest caution in using results based on the MHVD to inform management and restoration practices in the conifer forests of the American West.
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, 130 Mulford Hall, Berkeley, California, 94720, USA.
authors.forename: Carrie R
authors.initials: CR
authors.lastname: Levine
authors.affiliation: Harvard Forest, Harvard University, 324 North Main Street, Petersham, Massachusetts, 01366, USA.
authors.forename: Charles V
authors.initials: CV
authors.lastname: Cogbill
authors.affiliation: University of California Center for Fire Research and Outreach, College of Natural Resources, University of California, Berkeley, California, 94720, USA.
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Collins
authors.affiliation: Department of Forest Management, University of Montana, 32 Campus Drive, Missoula, Montana, 59812, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Larson
authors.affiliation: S. J. & Jessie E. Quinney College of Natural Resources, Utah State University, 5230 Old Main Hill, Logan, Utah, 84322, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Lutz
authors.affiliation: USDA Forest Service, Pacific Southwest Research Station, 1731 Research Park Drive, Davis, California, 95618, USA.
authors.forename: Malcolm P
authors.initials: MP
authors.lastname: North
authors.affiliation: Department of Environmental Science and Policy, University of California, Davis, One Shields Avenue, Davis, California, 95616, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Restaino
authors.affiliation: Department of Environmental Science and Policy, University of California, Davis, One Shields Avenue, Davis, California, 95616, USA.|USDA Forest Service, Pacific Southwest Region, 1323 Club Drive, Vallejo, California, 94592, USA.
authors.forename: Hugh D
authors.initials: HD
authors.lastname: Safford
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, 130 Mulford Hall, Berkeley, California, 94720, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Stephens
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, 130 Mulford Hall, Berkeley, California, 94720, USA.
authors.forename: John J
authors.initials: JJ
authors.lastname: Battles
mesh_terms: D002140:California; D016468:Forestry / Q000379:methods*; D065928:Forests; D008800:Mexico; D008954:Models, Biological; D015233:Models, Statistical; D011156:Population Density; D014197:Trees / Q000502:physiology*
keywords: California; Voronoi area; density; forest; plotless density estimator