Computer assisted quality control in tree ring dating and measurement
Computer assisted quality control in tree ring dating and measurement - country friends dating
To put the region's recent drought variability in a long-term perspective, a dense and diverse tree-ring network—including the first records throughout the Apalachicola–Chattahoochee–Flint river basin—is used to reconstruct drought from 1665 to 2010 CE.The network accounts for up to 58.1% of the annual variance in warm-season drought during the 20th century and captures wet eras during the middle to late 20th century.
In chronologies with less than three trees at the beginning of the chronology, variance was stabilized using a combination of rbar weighted and one-third spline methodology (Cook and Krusic 2011, Osborn 1997).In those cases, a cubic smoothing spline two-thirds the length of the series was used to reduce end-fitting issues (Cook and Peters 1981).The chronologies were stabilized in order to account for varying sample depth through time.Notably, the droughts of 1986–8, 1998–20–9 caused severe crop damage, disruptions in electricity generation and water shortages, which prompted water restrictions and multi-state legal conflicts (Cook 1988, Manuel 2008).This is particularly evident in the state of Georgia, where droughts during the 1980s and 1990s occurred concomitant with a 50% increase in population and a 35% increase in groundwater withdrawal (Fanning 2003).Map of tree-ring locations in the ACF river basin used for PDSI reconstruction.
Different symbols represent the period for the beginning year of each chronology.Because many series exhibited radial increment patterns typical of disturbance in closed-canopy forests (Lorimer 1985), individual series were standardized using a flexible curve (Pederson 2010, Friedman 1984).The Friedman Super Smoother sometimes caused distortion at either end of a series where ring-width measurements would trend up (down) while the standardization curve would trend down (up), resulting in an artificial upward (downward) trend in the resulting tree-ring index.The dendrochronology program library in R (dpl R) is able to read standard decadal-format files and allows users to perform several standard analyses including interactive detrending, chronology building, and the calculation of standard descriptive statistics.The package can also produce a variety of publication quality plots.I present and describe a new software package in the R statistical programming environment for dendrochronology.